876 |Me allomics, 2018, 10, 876--886 This jou nal is ©The Royal Socie y o Chemis y 2018
Ci e his: Me allomics, 2018,
10,876
The complex global esponse o coppe in he
mul icellula bac e ium Myxococcus xan hus
Juana Pe
´ ez, * Jose
´Mun
˜oz-Do ado and Au elio Mo aleda-Mun
˜oz
The complex coppe esponse o he mul icellula p o eobac e ium M. xan hus includes s uc u al genes
simila o hose desc ibed in o he bac e ia, such as P
1B
- ype ATPases, mul icoppe oxidases, and hea y
me al efflux sys ems. Howe e , he wo ime-dependen exp ession p o iles o he diffe en coppe
sys ems a e unique. The e a e a numbe o genes esponsible o an immedia e esponse, whose
exp ession inc eases a e he addi ion o coppe , bu apidly dec eases he ea e o basal le els. The
egula o y elemen ha con ols his ea ly esponse is Co E, a no el ex acy oplasmic unc ion s ac o
ha is ac i a ed by Cu
2+
and inac i a ed by Cu
+
. O he genes a e pa o a main enance esponse. These
genes show a p o ile ha slows up a e he coppe addi ion and eaches a pla eau a 24–48 h incuba ion.
Mos o he genes in ol ed in his esponse a e encoded by he ope on cu A, which is egula ed by he
wo-componen sys em Co SR. Mo eo e , o he genes in ol ed in he main enance esponse a e egula ed
by di e en egula o y elemen s ha emain unknown. Addi ionally, coppe ac i a es he ansc ip ion o
he s uc u al genes o ca o enoid syn hesis h ough a mechanism ha equi es he ac i a ion o he
s ac o Ca Q. Bea ing in mind ha M. xan hus is no e y esis an o coppe , i is specula ed ha he
complexi y o i s coppe esponse migh be ela ed o i s complex li e cycle.
In oduc ion
Coppe is a mic onu ien ansi ion me al wi h impo an
s uc u al and me abolic oles as a p os he ic g oup in key me allo-
p o eins in ol ed in essen ial p ocesses, such as espi a ion
Depa amen o de Mic obiologı
´a, Facul ad de Ciencias, Uni e sidad de G anada,
E-18071 G anada, Spain. E-mail: jp o es@ug .es
Le Jose
´Mun
˜oz Do ado, and igh Juana Pe
´ ez
P o . Jose
´Mun
˜oz Do ado s udied Biology a he Uni e si y
o G anada (Spain) whe e he also comple ed his PhD on
Myxobac e ia. He hen mo ed o he Uni e si y o Medicine and
Den is y o New Je sey, Uni ed S a es, as a pos -doc o al ellow
om 1988 o 1992. A e wa ds, he mo ed o Yokohama, Japan,
whe e he wo ked on yeas o Ki in B ewe y Co., om May 1992 o
Sep embe 1993, when he e u ned o he Uni e si y o G anada o
wo k as Assis an P o esso and la e as Associa e P o esso . Since
2009 he is Full P o esso o Mic obiology a he Uni e si y o
G anada. He is he leade o he P oka yo ic De elopmen G oup,
which esea ch is ocused on he complex mul icellula li es yle o
Myxococcus xan hus, mainly on he oles o pa alogous genes o
cope wi h changing en i onmen s, such as nu ien abundance o
he p esence o me als. We a e also in e es ed in diffe en aspec s o
he coope a i e p eda o y ac i i y o his bac e ia.
D Juana Pe
´ ez s udied Pha macy a he Uni e si y o G anada whe e he also comple ed his PhD. In 1989 she ecei ed a Fulb igh
Fellowship o wo king in enzymes in ol ed in lignin deg ada ion a he Fo es P oduc s Labo a o y in Madison (WI). In 1993, she
e u ned o Spain o wo k as pos doc o al esea che a he Ins i u e o Pa asi ology and Biomedicine o he Spanish Na ional Resea ch
Council (CSIC) and la e o he Uni e si y o G anada, whe e she wo ked as Assis an and Associa e P o esso . Since 2011 she is
Full P o esso o Mic obiology a he Uni e si y o G anada.
Recei ed 30 h May 2018,
Accep ed 21s June 2018
DOI: 10.1039/c8m 00121a
sc.li/me allomics
Me allomics
MINIREVIEW
Downloaded om h ps://academic.oup.com/me allomics/a icle/10/7/876/5952465 by Uni e sidad de G anada - Biblio eca use on 31 July 2025
This jou nal is ©The Royal Socie y o Chemis y 2018 Me allomics, 2018, 10, 876--886 | 877
and pho osyn hesis.
1
This is possible because coppe is a edox-
ac i e me al ha luc ua es be ween an oxidized (Cu
2+
) and a
educed (Cu
+
) s a e. Howe e , his high eac i i y is also he
eason why coppe can be oxic o cells. This me al is able no
only o gene a e eac i e oxygen species (ROS), bu i also binds
igh ly o he ac i e si es o many me alloenzymes, leading o
hei inac i a ion.
2–4
To deal wi h his pa adoxical ole and o
modula e he delica e cellula le els, all o ganisms, including
bac e ia, ha e de eloped a complex ne wo k o coppe handling
and a icking mechanisms.
5,6
Fo main aining coppe home-
os asis, bac e ia ac i a e he exp ession o speci ic genes ha
include e lux pumps, such as P
1B
- ype ATPases and hea y-me al
e lux sys ems ha belong o he esis ance-nodula ion-cell di ision
(HME-RND) supe amily.
7–9
Since coppe canno be deg aded,
bac e ia also ac i a e me allochape ones o i s seques a ion
and pe iplasmic mul icoppe oxidases (MCOs) o dec ease he
coppe oxici y in he cells h ough he oxida ion o oxic Cu
+
o
less oxic Cu
2+
. All o hese s uc u al genes mus be con olled
by me al-sensing egula o y ansc ip ion ac o s, ha is, by
me allo egula o y p o eins.
4,5,10,11
Myxococcus xan hus is a del ap o eobac e ium wi h a dis-
inc i e biological cycle among he p oka yo es and i is con-
side ed one o he ew bac e ia ha exhibi s clea mul icellula
beha io .
12,13
On solid su aces, od-shaped ege a i e cells
mo e in coo dina ed g oups o coope a i ely p ey on a wide
a ie y o mic oo ganisms.
14
In he absence o nu ien s, he
g oups o cells mo e oge he wi h o ganized gliding mo e-
men s and, a ce ain poin s, o m mac oscopic s uc u es
called ui ing bodies (Fig. 1). Du ing his s age, h ee diffe en
subpopula ions o cells show di ision o labo . A small pe cen-
age o cells diffe en ia e om ods in o sphe ical esis an
myxospo es, ano he ac ion o cells emain as pe iphe al ods,
and he majo i y o cells die, p esumably o p o ide nu ien s
o agg ega ion and spo e diffe en ia ion (Fig. 1).
13
M. xan hus
is mainly ound in soil and i s li e cycle mus he e o e be
accomplished in his a iable en i onmen wi h many luc ua ing
elemen s such as me als. Coppe is ound na u ally in soil a
concen a ions ha a y om 13 o 24 mg kg
1
, al hough
affic and ag icul u al, indus ial, mining and o he domes ic
ac i i ies a e con ibu ing o he inc ease o his me al in
he soil.
15
The M. xan hus coppe esponse diffe s om o he bac e ia
in many aspec s. Fi s , e lec ing he me abolic and s uc u al
diffe ences o he cells du ing hei li e cycle, de eloping and
g owing cells show diffe en esis ance o coppe (60 mM and
900 mM, espec i ely). Howe e , cells om bo h s ages exhibi
simila inc eased le els o me al esis ance (up o 2000 mM)
Fig. 1 Myxococcus xan hus mul icellula li e cycle. (A) Vege a i e g ow h.
On solid su aces, od-shaped ege a i e cells (yellow ods) mo e in
sea ch o he p ey in a coo dina ed manne , o ming dynamic mul icellula
g oups, which eed coope a i ely p eying on a wide a ie y o mic o-
o ganisms (he e ep esen ed as o ange ods). Cells sec e e hyd oly ic
enzymes and seconda y me aboli es ha kill and lyse he p ey (ligh g ey
ods). (B) De elopmen al cycle. In he absence o nu ien s, g oups o cells
o ganize hei mo emen s and o m mac oscopic ui ing bodies wi h
h ee diffe en subpopula ions. The majo i y o cells die (ligh yellow ods).
A small ac ion o cells emains as pe iphe al ods and he es o he od
cells de elop in o esis an ound myxospo es (yellow balls). This complex
cycle mus be accomplished in he a iable soil en i onmen , whe e one o
he luc ua ing elemen s is coppe .
D Au elio Mo aleda Mun
˜oz
s udied Biology a he Uni e si y
o G anada (Spain) whe e he
also ecei ed his PhD unde
he guidance o P o esso Jose
´
Mun
˜oz-Do ado in 2003. He sub-
sequen ly pu sued pos -doc o al
esea ch wi h P o esso Law ence
J. Shimke s a he Uni e si y
o Geo gia om Ma ch 2005 o
Ap il 2007, when he e u ned
o he Uni e si y o G anada o
wo k as pos doc o al esea che .
He became an Assis an P o esso
in he Depa men o Mic obio-
logy a he Uni e si y o G anada
in 2012.
Au elio Mo aleda-Mun
˜oz
Mini e iew Me allomics
Downloaded om h ps://academic.oup.com/me allomics/a icle/10/7/876/5952465 by Uni e sidad de G anada - Biblio eca use on 31 July 2025
878 |Me allomics, 2018, 10, 876--886 This jou nal is ©The Royal Socie y o Chemis y 2018
when cul u es a e p e-incuba ed wi h coppe , indica ing an
induc ion o a esis ance pheno ype by adap a ion.
16
Second,
al hough M. xan hus is no especially esis an o his me al
compa ed o o he bac e ia, i s genome encodes a la ge numbe
o genes in ol ed in coppe homeos asis (Fig. 2).
16–18
Thi d,
his ex ensi e coppe egulon is o ches a ed by di e se and
speci ic egula o y elemen s ha allow M. xan hus o eac o
coppe in a hie a chical way, wi h some o he genes in ol ed
in an immedia e esponse and o he s in sus aining such a
esponse.
19,20
And ou h, his bac e ium accumula es ca o enoids,
p obably o quench single oxygen gene a ed by his me al, a
mechanism no epo ed o any o he bac e ium.
21
In his e iew
we ocus on he mos in e es ing aspec s o he complexi y o he
M. xan hus coppe esponse.
Sea ching o sys ems in ol ed in he
M. xan hus global coppe esponse
An in silico analysis o he M. xan hus genome e ealed a high
numbe o genes in ol ed in coppe and/o o he me al homeo-
s asis, including h ee P
1B
- ype ATPases named copA,copB, and
copC,
18
h ee MCOs named cuoA,cuoB, and cuoC,
16
and six
HME-RND hea y me al efflux sys ems.
17
In acco dance wi h he
analysis o sequence signa u es in ansmemb ane domains
desc ibed p e iously,
22,23
h ee o hose ipa i e efflux com-
plexes we e classi ied as Cus sys ems (Cus1, Cus2, and Cus3),
hough o be in ol ed in he expo o Cu
+
and o he mono-
alen me als, while he o he h ee we e classi ied as Czc
sys ems (Czc1, Czc2, and Czc3), hough o be in ol ed in
cobal , zinc, and cadmium efflux.
17
Mos o hese wel e sys ems
a e encoded in wo main egions o he M. xan hus genome.
17
One o he s a egies used o s udy he ole o hese genes in
coppe homeos asis was o ollow hei exp ession p o iles in
he absence and p esence o coppe and o he me als. These
expe imen s e ealed ha many gene exp essions we e coppe
dependen and diffe en ially egula ed, sugges ing a sophis i-
ca ed ne wo k no only o s uc u al p o eins bu also o me al
senso s (Fig. 2). In mos cases, de eloping cells eached he
same le els o coppe -dependen exp ession wi h 10- old
lowe me al concen a ions,
16–18
mos likely due o me abolic
and s uc u al di e ences be ween cells in he wo phases o
he li e cycle. Ac ually, he physiological s age o cells is an
impo an ac o in coppe ole ance, as epo ed o di e -
ences be ween he ae obic and anae obic coppe esponse in
Esche ichia coli.
24
Two majo exp ession p o iles a e clea ly obse ed in genes
up- egula ed by coppe in M. xan hus. One is exhibi ed by he
MCO cuoB and he P
1B
- ype ATPase copB (Fig. 3A). These wo
genes a e apidly up- egula ed upon he addi ion o coppe ,
eaching a maximum a 2 h. A e wa ds he exp ession dec eases
o a e y basal le el. The ac ha dele ion mu an s in hese wo
genes a e ma kedly mo e sensi i e o coppe han he wild- ype
s ain indica es ha hey ep esen he i s line o de ense
Fig. 2 M. xan hus global coppe esponse. The genomic en i onmen o he genes and he sub-cellula localiza ion o he p o eins a e ep esen ed. The
MCOs (b own) CuoA, CuoB, and CuoC a e pe iplasmic p o eins ha oxidize Cu
+
(g ey balls) o he less oxic Cu
2+
(blue balls) h ough hei cup ous
oxidase ac i i y. The P
1B
- ype ATPases (ligh g een) CopA and CopB ex ude Cu
+
om he cy oplasm o he pe iplasm. The HME-RND pumps, he
Cus-like sys ems Cus2 and Cus3, de oxi y he cy oplasm and he pe iplasm by pumping coppe o he ex e io . MXAN_3414 (pu ple) is a p o ein esembling
he subuni III o he cbb3- ype Cy och ome c oxidases. MXAN_3427 (pink) encodes a p o ein wi h a hea y me al-associa ed domain. The wo egula o y
elemen s ( ed) a e he wo-componen sys em Co SR and he coppe -dependen ECF sigma ac o Co E. See ex o de ails.
Me allomics Mini e iew
Downloaded om h ps://academic.oup.com/me allomics/a icle/10/7/876/5952465 by Uni e sidad de G anada - Biblio eca use on 31 July 2025
This jou nal is ©The Royal Socie y o Chemis y 2018 Me allomics, 2018, 10, 876--886 | 879
agains he s ess gene a ed by coppe , whe e hey a e in ol ed
in wha has been called an immedia e esponse (IR).
In con as , i e o he genes, cuoA,cuoC,copA,cus2, and cus3,
show a e y diffe en p o ile du ing g ow h, in which exp ession
goes up slowly a e he coppe addi ion, eaching maximum
le els a 24 h (Fig. 3B). Fo his eason, hese genes pa icipa e
in he main enance o he esponse (MR) o his me al. As wi h
he IR genes, he de elopmen al coppe - esponsi e exp ession
p o iles o cuoA,copA,cus2, and cus3 a e simila o hose shown
du ing g ow h, al hough wi h only 1/10 o he me al concen-
a ion in he medium. Howe e , he MCO cuoC exhibi s
an induc ion du ing de elopmen which is independen o
coppe .
18
The pheno ypes o he mu an s indica e ha all o
hese i e genes a e in ol ed in con e ing coppe ole ance
o M. xan hus.
16–18
Rega ding he es o he genes (copC,cus1,czc1,czc2, and
czc3), hey a e no conside ed o pa icipa e in he coppe
esponse since hey a e no up- egula ed by his me al and
he dele ion mu an s do no exhibi a signi ican inc ease in
coppe sensi i i y compa ed wi h he wild- ype s ain.
17,18
In
summa y, se en genes we e ini ially iden i ied as pa icipa ing
in con e ing coppe ole ance o M. xan hus. Two o hem
(copB and cuoB) pa icipa e in he IR, while he o he s (copA,cuoA,
cuoC,cus2,andcus3) pa icipa e in he MR.
The pa icipa ion o h ee diffe en pe iplasmic MCOs,
which a e able o oxidize Cu
+
o Cu
2+
, in he M. xan hus coppe
esponse migh e lec he need o his bac e ium o achie e
a ine adjus men o he oxida ion s a e o coppe in he
pe iplasm.
16
This may be ela ed o he unique s uc u e o
he M. xan hus pep idoglycan, which is equi ed o pe mi he
con e sion o he long ege a i e ods in o coccoid myxospo es
du ing de elopmen .
13
In ac , he accumula ion o Cu
+
in
he M. xan hus pe iplasm o he MCO mu an s induces he
mo phology o he g owing cells o change om ods o sphe ical
o ms.
16
In bo h esponses (IR and MR), he coincidence in he
exp ession p o iles o a P
1B
- ype ATPase wi h a MCO (CuoB wi h
CopB and CuoA–CuoC wi h CopA) (Fig. 3) indica es ha hey
unc ion oge he , wi h he Cop p o ein ex uding Cu
+
om he
cy osol o he pe iplasm, whe e he cogna e Cuo p o eins oxidize
Cu
+
o he less oxic o m Cu
2+
h ough hei demons a ed
cup ous oxidase ac i i y.
16
Co E, a coppe -dependen RNA
polyme ase sigma ac o wi h a
su p ising mechanism o ac ion,
egula es he M. xan hus coppe
immedia e esponse
The analysis o he genomic en i onmen o he IR genes cuoB
and copB (Fig. 2) e ealed a gene, MXAN_3426, wi h s ong
simila i ies o ex a cy oplasmic unc ion (ECF) sigma ac o s,
which could be esponsible o he IR. This gene has been
named co E. RT-PCR assays ha e p o ed ha co E o ms an
ope on wi h cuoB and a gene (MXAN_3424) encoding a p o ein
wi h simila i ies o ou e memb ane efflux p o eins (OEPs).
19
OEPs a e channels ha allow he expo o a a ie y o
subs a es and ha may also be in ol ed in he ex usion o
coppe om he pe iplasm o he ex e io .
22
Mo eo e , gene
MXAN_3427 encodes a p o ein wi h a hea y me al-associa ed
domain (Fig. 2). S udies on Co E ha e demons a ed ha i
egula es he exp ession no only o cuoB and MXAN_3424, bu
also ha o copB and MXAN_3427. Fu he mo e, Co E pa ially
egula es he exp ession o he MR gene copA.
19
The es o he
genes analyzed (cuoA,cuoC,copC,cus1,cus2,cus3,czc1,czc2,
and czc3) a e no egula ed by Co E. The e o e, a o al o six
genes ha e so a been ound o pa icipa e in he IR, all o
which a e egula ed by Co E (Table 1).
One in iguing ques ion is how Co E unc ions. Co E esem-
bles ECF s ac o s, which a e small al e na i e s ac o s, a he
di e gen in sequence, ha con ain only wo egions (s2ands4)
Fig. 3 The M. xan hus coppe esponse is o ganized in a ime-dependen
manne inanimmedia eandamain enance esponse. Speci ic b-galac osidase
ac i i ies we e measu ed in he cell ex ac s o s ains ha bo ing usions
be ween he p omo e o each gene and lacZ, which we e g own in he
p esence o 600 mM coppe . (A) IR is ep esen ed by cuoB (blue) and copB
( ed) p o iles. (B) MR is exempli ied by cuoA (blue) and copA ( ed). Red awn
om 20 Sa
´nchez-Su il e al., 2013
20
and Go
´mez-San os e al., 2011
19
(wi h
pe mission o he au ho s).
Mini e iew Me allomics
Downloaded om h ps://academic.oup.com/me allomics/a icle/10/7/876/5952465 by Uni e sidad de G anada - Biblio eca use on 31 July 2025
880 |Me allomics, 2018, 10, 876--886 This jou nal is ©The Royal Socie y o Chemis y 2018
ou o he ou ound in he housekeeping s ac o . These wo
egions a e equi ed o in e ac ion wi h he RNA polyme ase
co e enzyme and ecogni ion o he p omo e .
25,26
ECF s ac o s
ep esen he hi d pilla o bac e ial signal ansduc ion, and
hey modula e ansc ip ion, al e na ing be ween an ac i e
and an inac i e s a e. Canonical ECF s ac o s a e equen ly
egula ed by a memb ane-ancho ed p o ein known as an an i-s
ac o , which seques e s he s ac o in he absence o s imuli,
he eby keeping i inac i e. Upon ecei ing a p ope signal, he
an i-sis inac i a ed and eleases he s ac o , which can now
di ec he exp ession o he a ge genes a e he ec ui men
o he RNA polyme ase.
25
Al hough many ECF s ac o s a e
egula ed h ough an an i-s ac o , diffe en modes o egula ing
ECF s ac o s’ ac i i ies ha e been desc ibed. Cu en ly, ECF
s ac o s a e classi ied in o 50 g oups.
26,27
Mos ECF s ac o s a e co-exp essed wi h hei cogna e an i-
s ac o ,
26
bu in he case o Co E, he e was no good candida e
ha migh unc ion as an an i-s ac o in he neighbo hood
egion. Ne e heless, he an i-s ac o could be encoded in any
o he egion o he M. xan hus ch omosome. To answe he
ques ion o whe he Co E wo ks in coope a ion wi h an uni-
den i ied an i-s ac o , Co E was o e -exp essed in a Dco E
cuoB-lacZ s ain, and he exp ession o cuoB was analyzed. I is
assumed ha sand an i-s ac o s mus be in a 1 : 1 a io o
p ope ly unc ion. The e o e, i he s ac o is o e -exp essed,
his p o ein would be p esen in a highe quan i y han he
cogna e an i-s ac o and, in consequence, he emaining ee
s ac o would unc ion in he absence o s imulus, which in
he case o Co E would be in he absence o coppe . Quali a i e
and quan i a i e analyses demons a ed ha o e -exp ession o
Co E did no lead o exp ession o cuoB in he absence o
coppe . Mo eo e , coppe addi ion yielded e y simila exp es-
sion p o iles o cuoB in he wild- ype s ain and in he s ain
whe e Co E was o e -exp essed, indica ing ha Co E unc ions
wi hou an an i-s ac o .
19
This obse a ion aised he ques ion
o how Co E esponds o coppe addi ion. Se e al in i o
and in i o analyses demons a ed ha Co E unde goes a
sensi iza ion/desensi iza ion p ocess whe eby he egula o is
ac i e du ing a limi ed pe iod o ime a e he con ac wi h
coppe , which is dependen on he edox s a e o coppe
(Fig. 4). These da a allowed he elabo a ion o a model in which
Co E is ac i a ed by Cu
2+
, which mos likely changes i s con-
o ma ion o he ac i e s a e o bind he DNA and o p omo e
he ansc ip ion (Fig. 4C and D). Once he immedia e esponse
has been igge ed by Co E, he educing condi ions o he cy osol
would a o he o ma ion o Cu
+
, inac i a ing he s ac o and
e mina ing he immedia e esponse (Fig. 4E).
19
Acco ding o his model, Co E mus speci ically ecognize
coppe . The de ailed s udy o he sequence o Co E e ealed
ha i exhibi s a C- e minus ex ension called CRD ( o Cys ich
domain) and a conse ed CxC mo i loca ed be ween he s2
and he s4 egions (Fig. 4A and B). S udies using in- ame
dele ion mu an s o he CRD and si e-di ec ed mu agenesis in
diffe en Cys esidues demons a ed ha bo h he CxC and
CRD a e essen ial o Co E ac i i y.
19,28
Mo eo e , i was also
demons a ed ha Cys189 (Fig. 4A) is he main esidue o he
CRD in ol ed in he sensi iza ion o Co E, because his single
mu a ion abolishes 93% o he me al esponse. Simila ly, Cys184
(Fig. 4A) seems o be essen ial o he desensi iza ion p ocess
because he exp ession p o ile o he genes egula ed by he
Co E
C184A
s ain exhibi ed a sus ained coppe esponse o e ime,
wi h no peak a 2 h.
19
In conclusion, Co E is a coppe -dependen
ECF s ac o ha unc ions wi hou an an i-s ac o , whose ac i e
and inac i e s a es a e egula ed by a CxC mo i and a CRD ha
de ec he edox s a e o coppe (Fig. 4).
Based on he abo e esul s, Co E is no only he ounde
membe o a new g oup o ECF s ac o s, named Co E-like o
ECF44,
27
bu i also ep esen s a new class o me al-sensing
egula o .
11
The M. xan hus genome codes o a second ECF s ac o ha
also con ains a CRD, which is loca ed in a gene ic en i onmen
con aining genes ha code o p o eins wi h simila i ies o me al-
de oxi ica ion p o eins.
28
This second membe o he g oup
was named Co E2 (Fig. 4A). Co E2 exhibi s se e al simila i ies
Table 1 P edic ed p o eins o he locus in ol ed in he immedia e esponse egula ed by Co E, and he cu A ope on in ol ed in he main enance
esponse and con olled by Co SR. The domains in he da abase P am a e in pa en heses
MXAN_ P o ein P edic ed unc ion P edic ed localiza ion
Immedia e esponse (IR)
3415 CopA Coppe - ansloca ing P
1B
- ype ATPase (PF04945, PF00122, PF02954) Memb ane p o ein
3422 CopB Coppe - ansloca ing P
1B
- ype ATPase (PF00403, PF00122, PF00702) Memb ane p o ein
3424 3424 Ou e memb ane efflux p o ein (PF02321) Ex e nal memb ane p o ein
3425 CuoB Mul icoppe oxidase (PF07732, PF07731) Pe iplasmic
3426 Co E ECF s ac o (PF04542, PF08281) Cy oplasmic
3427 3427 Hea y-me al-associa ed domain (PF00403) Cy oplasmic
Main enance esponse (MR)
3413 3413 Hypo he ical p o ein Pe iplasmic
3414 3414 Cy och ome c oxidase, cbb3- ype, subuni III (PF13442) Pe iplasmic
3415 CopA Coppe - ansloca ing P
1B
- ype ATPase (PF04945, PF00122, PF02954) Pe iplasmic
3416 3416 Lipop o ein con aining DUF305 domain (PF03713) Memb ane p o ein
3417 3417 Lipop o ein con aining wo PQQ_2 domains (PF13360) P obably ex e nal memb ane lipop o ein
3418 Co R s54-dependen DNA-binding esponse egula o (PF00072, PF00158, PF02954) P obably ex e nal memb ane lipop o ein
3419 Co S Signal ansduc ion his idine kinase (PF02518, PF00512, PF13581, PF00672, PF13589) Cy oplasmic
3420 CuoA Mul icoppe oxidase (PF07732, PF07731, PF00394) Memb ane p o ein
3421 3421 P o ein wi h His- ich egion, cup edoxin1 (PF13473) Pe iplasmic
Me allomics Mini e iew
Downloaded om h ps://academic.oup.com/me allomics/a icle/10/7/876/5952465 by Uni e sidad de G anada - Biblio eca use on 31 July 2025
This jou nal is ©The Royal Socie y o Chemis y 2018 Me allomics, 2018, 10, 876--886 | 881
wi h Co E, such as unc ioning wi hou an an i-s ac o and
being egula ed by me als. Howe e , Co E2 also exhibi s clea
diffe ences om Co E. Thus, cadmium and zinc, bu no
coppe , ac i a e his s ac o . Mo eo e , al hough genes egula ed
by his s ac o also each a maximum exp ession a 2 h, hese
le els dec ease slowly he ea e , emaining qui e close o he
maximum e en a 48 h. This diffe ence in he exp ession p o ile
can be explained by he ac ha , in con ac o coppe , cobal
and cadmium a e edox-inac i e me als. Acco dingly, once hey
en e he cy oplasm and ac i a e Co E2, he ac i a ion will be
main ained h ough ime because he edox s a e o hese
me als will emain unal e ed.
28
These da a ob ained om
Co E2 ein o ce he idea ha he coppe edox s a e is espon-
sible o he ac i a ion and inac i a ion o Co E.
19,28
In o de o look mo e closely a he mechanism o ac ion o
he wo membe s o his new g oup, and especially o in es i-
ga e how hese wo me al-sensing p o eins dis inguish be ween
diffe en me als, all he cys eines and o he esidues on Co E2
CRD we e mu a ed. Al hough he Cys mo i is well conse ed
wi hin he wo s ac o s, he e is one Cys (Cys174 in Co E2) ha
is no p esen in Co E, whe e an Ala is ound (Fig. 4A). In e -
es ingly, he mu an Co E2
C174A
did no espond o cadmium,
bu only o coppe . Mo eo e , he opposi e change, ha is,
he eplacemen o he Ala185 wi h a Cys in he CRD o Co E,
did no change he Co E affini y o coppe . Howe e , up-
egula ion o he exp ession o genes egula ed by Co E in he
p esence o cadmium was h ee imes highe in he mu an
A185C han in he wild- ype s ain. These da a sugges ha he
Cys a angemen o he CRD de e mines he me al speci ici y.
28
Mo eo e , i is wo h men ioning ha unpublished esul s o
ou g oup in collabo a ion wi h S. A ian and M. Capde illa
ha e e ealed ha he binding o Cu/Zn o Co E o Cd/Zn o
Co E2 induces impo an con o ma ional changes in he
a-helices o hese wo s ac o s, which mos likely a e espon-
sible o modula ing hei signaling mechanism.
A bioin o ma ic sea ch has allowed he iden i ica ion in
diffe en phyla o Bac e ia 67 s ac o s ha exhibi a Co E-like
a chi ec u e wi h a highly conse ed Cys a angemen loca ed
a he C- e minus. Al hough mos o he p o eins belong o he
o de Myxococcales, hey a e also p esen in al a, be a, and
gamma P o eobac e ia,Acidobac e ia,Chlamydia/Ve icomic obia,
and Spi ochae a.
28
The main enance esponse is mainly
modula ed by he wo-componen
sys em Co SR
The main enance esponse (MR) o M. xan hus o iginally com-
p ised i e genes (cuoC,cus2,cus3,cuoA, and copA). Howe e , as
he MCO cuoA and he P
1B
-ATPase copA o m an ope on (cu A)
wi h ano he se en genes (Table 1), a o al o wel e genes mus
be conside ed as pa o he MR. The diffe en p o iles exhibi-
ed by genes o he MR compa ed o genes in ol ed in he IR
(Fig. 3) clea ly show ha his MR mus be modula ed by
diffe en me allosenso p o eins. In ac , he e a e wo genes
in he cu A ope on ha show simila i ies o a wo-componen
sys em, called Co SR, whe e Co S is he his idine kinase (HK)
and Co R is he esponse egula o (RR), which is esponsible
o he exp ession o he cu A ope on, bu no o cuoC,cus2,
o cus3.
20
Th ee lines o e idence e lec ha al hough cu A con e s
coppe esis ance du ing g ow h, i is especially impo an o
he de oxi ica ion o he cells du ing de elopmen . Fi s , Dco SR
cells accumula e 13- old mo e coppe han hose o he wild-
ype s ain du ing de elopmen , bu only 1.3- old mo e du ing
g ow h. Second, he effec o his mu a ion on ui ing body
o ma ion is mo e d ama ic han on g ow h. Thus, adap ed
cells o he mu an ole a e hal as much coppe as he wild-
ype s ain du ing g ow h. Con e sely, al hough he mu an
de eloping cells could ole a e simila coppe concen a ions
han g owing cells, hey could build ui ing bodies wi h 25- old
less coppe han he wild- ype s ain. Highe concen a ions
blocked agg ega ion bu did no kill he cells. And hi d,
he exp ession o de elopmen al genes ha a e exp essed la e
in de elopmen is clea ly impai ed in he Dco SR mu an .
20
Sequence analyses using diffe en bioin o ma ic app oaches
e ealed ha Co S has a cy oplasmic egion exhibi ing modula
o ganiza ion wi h h ee conse ed domains: a HAMP domain,
Fig. 4 Mechanism o ac ion o he new g oup o Co E-like me al-dependen
ECF s ac o s. (A) Domain a chi ec u e o he wo ECF s ac o s o M. xan hus.
Co E and Co E2 ha e he domains s2(PF04542)ands4 (PF08281) dis inc i e
o all ECF sigma ac o s. Be ween bo h domains, he e is a conse ed
sequence con aining a CxC mo i ha is essen ial o he ac i i y. A cha -
ac e is ic CRD ( o Cys ich domain) in ol ed in me al de ec ion is loca ed
a he C- e minal domain. (B) In he absence o me al, Co E emains
inac i e and i is unable o bind o DNA. (C and D) In he p esence o Cu
2+
(blue balls), he p o ein u ns ac i e, allowing binding o he co e RNA
polyme ase and DNA a he 35 and 10 egions, and s a ing ansc ip-
ion. (E) In he educing en i onmen o he cy oplasm, he edox s a e o
coppe apidly changes o Cu
+
(g ey balls) and he p o ein again changes
i s con igu a ion o become inac i e.
Mini e iew Me allomics
Downloaded om h ps://academic.oup.com/me allomics/a icle/10/7/876/5952465 by Uni e sidad de G anada - Biblio eca use on 31 July 2025
882 |Me allomics, 2018, 10, 876--886 This jou nal is ©The Royal Socie y o Chemis y 2018
a kinase co e consis ing o a dime iza ion and a his idine
phospho ans e domain (DHp), and he ca aly ic and ATPase
domain (CA) (Fig. 5). The p o ein is ancho ed o he memb ane
h ough wo p edic ed ansmemb ane-spanning domains
and con ains a pe iplasmic senso domain ha consis s o
158 esidues. The senso domain only exhibi s simila i ies wi h
o he pe iplasmic domains o HKs om diffe en bac e ia o
he o de Myxococcales.
29
The p edic ed seconda y s uc u e o
his domain allowed i o be included in he ‘‘all-alpha’’ p o ein
g oup, and i he e o e o ms pa o he ‘‘all helical old’’
senso class.
30
This esul is e y in e es ing because his class
includes HKs which a e no in ol ed in coppe sensing, such as
Na X om E. coli,
31
as well as To S om E. coli and Vib io
pa ahaemoly icus.
32
In con as , o he senso domains o HKs
in ol ed in bac e ial coppe homeos asis, such as CinS om
Pseudomonas pu ida,
33
CopS om Synechocys is sp.
34
and CusS
om E. coli
35
a e included in he ‘‘mixed alpha-be a old’’
class.
29
These obse a ions indica e ha he mechanism o
signal ansmission o Co S mus diffe om ha o o he
coppe senso HKs. The diffe ence could be due o he ac ha
he o he senso s ecognize Cu
+
, while Co S de ec s Cu
2+
.
16
To look mo e closely a his mechanism o signal ans-
mission o Co S, he pe iplasmic senso domain was dis-
sec ed by cons uc ing a se ies o sys ema ic in- ame dele ion
mu a ions. A small egion o 28 esidues loca ed a he
N- e minal sequence o he a1-helix and 9 esidues a he
C- e minal sequence o he a4-helix o he pe iplasmic egion
ha e been ound o be essen ial o coppe - egula ed gene
exp ession (Fig. 5).
29
The analysis o si e-di ec ed mu agenesis mu an s o he wo
His (His38 and His171) p esen in hose egions and a hi d, well
conse ed, His (His34) ha emained in all dele ion mu an s and
ha is also loca ed in he a1-helix, showed ha hese h ee
esidues a e essen ial o ac i a ion o his kinase by coppe .
In i o in e ac ion s udies using a bac e ial wo-hyb id sys em
e ealed ha al hough Co S o ms a homodime in he absence
o coppe , he addi ion o he me al a o s dime iza ion. These
esul s sugges ha coppe plays a ole in bo h dime iza ion and
ansmission o he signal. The cu en hypo hesis is ha coppe
binding is achie ed in he con ex o a dime ic senso , whe e he
His34, His38, and His171 o bo h monome s a e implica ed in
coppe coo dina ion (Fig. 5). The changes induced by he coppe
binding migh ein o ce o s abilize he senso dime iza ion, and
such con o ma ional changes would be ansduced h ough he
HAMP domain in o he cy oplasmic domain. In hose ci cum-
s ances, he kinase ac i i y media ed by he ca aly ic domain
would be ac i a ed and Co S would be au ophospho yla ed. The
phospho yla ed Co S would allow he phospho ans e o i s
cogna e RR, Co R, which could hen p omo e he ansc ip ion
o he cu A ope on.
29
Co R is a DNA-binding p o ein ha shows
he ypical domain a chi ec u e o G oup I o he bac e ial
enhance binding p o eins (bEBPs).
20
Fo his eason, i may
be p edic ed ha Co R ac i a es he exp ession o genes om
p omo e s ecognized by he co e RNA polyme ase associa ed
wi h s54.
20,36
Fou diffe en sequences wi h simila i ies o
p omo e s o s54 we e iden i ied jus ups eam o ou genes
wi hin he cu A ope on, indica ing ha ansc ip ion ac i a ed by
Co R/s54 could be ini ia ed a diffe en si es.
20
This ac would
explain why he exp ession p o iles obse ed o genes o his
ope on diffe no only in he le els ob ained o each one, bu
also in he iming o when he pla eau is eached.
16,18,20
The
complexi y o he exp ession o cu A is u he suppo ed by he
ac ha copA is egula ed no only by Co SR, bu also by Co E,
20
so his ATPase pa icipa es in bo h he MR and he IR. These
esul s e lec he ac ha M. xan hus needs a e y p ecise
adjus men o all he coppe homeos asis mechanisms no only
o e ime, bu also h oughou i s en i e mul icellula li e cycle.
A no ewo hy applica ion o hese s udies, which has had g ea
accep ance in he in e na ional scien i ic communi y s udying
myxobac e ia, is he use o he s ong coppe -dependen p omo e
o cuoA ocons uc ase o plasmid ec o s ha allowcondi ional
coppe -inducible gene exp ession in M. xan hus.
37,38
The biosyn hesis o ca o enoids and
in e connec ions be ween diffe en
mechanisms in ol ed in coppe
homeos asis
Ca o enoids a e ed colo ed isop enoids equen ly p oduced
by pho osyn he ic bac e ia o p o ec agains pho ooxida i e
damage since hey a e able o quench single oxygen (
1
O
2
) and
Fig. 5 M. xan hus Co S signal- ansduc ion model. Schema ic ep esen-
a ion o he modula o ganiza ion o he cy oplasmic po ion o Co S, wi h
he HAMP domain ( ed ec angle), and he DHp and CA domains ypical o
HKs. The ou ahelices o he pe iplasmic senso domain a e ep esen ed
as ec angles, colo ed in o ange, ligh g ey, da k g ey, and g een (helices 1,
2, 3, and 4, espec i ely). In he absence o coppe Co S is a homodime .
His34 and His38, wi hin he a1-helix, and His171, in he a4-helix, a e in ol ed
in coppe coo dina ion. The p esence o Cu
2+
(blue balls) enhances he
endency o he domain o dime ize and hese changes help o ansmi he
signal h ough he HAMP domain o he ca aly ic domain.
Me allomics Mini e iew
Downloaded om h ps://academic.oup.com/me allomics/a icle/10/7/876/5952465 by Uni e sidad de G anada - Biblio eca use on 31 July 2025
This jou nal is ©The Royal Socie y o Chemis y 2018 Me allomics, 2018, 10, 876--886 | 883
o he eac i e oxygen species ha can damage cell compo-
nen s.
39
Al hough M. xan hus is a non-pho o ophic bac e ium,
blue ligh igge s a complex ansc ip ional esponse leading
o he biosyn hesis o ca o enoids.
40–42
This p ocess is egu-
la ed by a canonical ECF s/an i-s ac o sys em (Ca Q–Ca R),
which wo ks in coo dina ion wi h he pho o ecep o Ca F
ac ing as an an i–an i-s ac o . Genes coding o Ca Q, Ca S,
and Ca R o m he ope on ca QRS, which is con olled by he
ligh -inducible p omo e P
QRS
.
43,44
B ie ly, in he p esence o
ligh , Ca R is somehow inac i a ed in a p ocess ha equi es
he ac ion o he an i–an i-s ac o Ca F, libe a ing he s ac o
Ca Q. F ee Ca Q ec ui s he co e RNA polyme ase, s a ing he
ansc ip ion o he ca o enoid biosyn hesis s uc u al genes.
These genes a e loca ed a wo unlinked loci, he ca B ope on
(wi h six genes) and he gene c I, which a e egula ed by he
p omo e s P
B
and P
I
, espec i ely.
45–47
The P
B
p omo e is
down- egula ed in he da k by he ep esso p o ein Ca A,
which is encoded in he cons i u i ely exp essed ca A ope on,
loca ed jus downs eam o ca B.
48,49
Ca S media es he de ep es-
sion o he ca B ope on, which along wi h he Ca Q-media ed
ac i a ion o c I leads o he accumula ion o ca o enoids (Fig. 6).
Howe e , i has been demons a ed ha coppe also induces
ca o enogenesis in he da k.
21
Gene ic s udies using a collec-
ion o mu an s in s uc u al and egula o y genes e ealed ha
coppe -induced ca o enoid syn hesis is ca ied ou h ough
ansc ip ional ac i a ion o he same s uc u al genes ac i a ed
by ligh (Fig. 6). All o he egula o y elemen s in ol ed in he
ligh -induced ca o enogenesis also pa icipa e in he coppe
esponse, wi h he only excep ion being he ca F p oduc . In o he
wo ds, coppe seems o di ec ly inac i a e Ca R.
21
Howe e , some aspec s o he ca o enoid esponse o coppe
emain o be elucida ed. Fo ins ance, how coppe ac i a es he
biosyn hesis o ca o enoids, bea ing in mind ha i is nei he
induced by o he me als no by o he compounds ha gene a e
oxida i e s ess such as hyd ogen pe oxide, -bu ylhyd ope oxide
and pa aqua . Al hough
1
O
2
was o iginally p oposed as he mos
easible candida e esponsible o igge ing his esponse, i has
been epo ed ha Ca F media es signaling by he
1
O
2
gene a ed
ia pho oexci ed p o opo phy in IX.
50
Howe e , coppe -media ed
ca o enoid syn hesis is independen o Ca F, and he e o e he
mechanism used o ansmi he signal o he Ca Q–Ca R sys em
mus be di e en .
Ano he unanswe ed ques ion is why he biosyn hesis o
ca o enoids induced by coppe is mo e effec i e when cells a e
a subop imal g ow h condi ions. The easons o his physio-
logical modula ion o he ca o enogenic esponse could be
ela ed o he ac i i y o some o he p o eins desc ibed abo e
as being in ol ed in coppe homeos asis. In his espec , i is
wo h men ioning ha he mu an Dco SR accumula es ca o e-
noids a lowe coppe concen a ions han he wild- ype s ain
due o he lack o exp ession o MXAN_3414 (Fig. 2 and Table 1).
The DMXAN_3414 s ain no only induces he biosyn hesis o
ca o enoids a lowe coppe concen a ions du ing g ow h, bu
i is he only s ain ha builds ed ui ing bodies du ing
de elopmen .
20
One easonable explana ion o his pheno ype
is ha his gene could be equi ed o ene gy p oduc ion unde
coppe s ess. The e o e, he absence o his p o ein in he
mu an could dec ease ene gy le els, imi a ing subop imal
g ow h condi ions and consequen ly inducing he biosyn hesis
o ca o enoids a lowe coppe concen a ions. In suppo o
his hypo hesis is he high homology exhibi ed by MXAN_3414
wi h he subuni III o cbb3-Cox ( ha belongs o he P am
PF13442). Se e al au ho s ha e p e iously epo ed ha in o he
bac e ia, such as Pseudomonas luo escens
51
and Salmonella
yphimu ium,
52
he e is a connec ion be ween coppe esis ance,
Cox biogenesis, and compe i i e i ness. Since i is usual in
some bac e ia o ha e se e al espi a o y oxidases o allow cells
o adap hei espi a o y sys ems o he demands o a a ie y o
en i onmen al condi ions, including diffe en concen a ions
o me al ion co ac o s, i is possible ha he MXAN_3414 gene
Fig. 6 Model summa izing some o he desc ibed elemen s o he
egula o y ne wo k equi ed o ac i a ion o he ca o enogenesis in
M. xan hus. Ligh exci es p o opo phy in IX o a high-ene gy s a e, which
hen in e ac s wi h molecula oxygen o gi e
1
O
2
(yellow balls).
1
O
2
unc-
ions as he signal o he an i–an i-sCa F o in e ac wi h he an i-sCa R,
which in u n libe a es he ECF s ac o Ca Q. A e ec ui men o he co e
RNA polyme ase, Ca Q ac i a es he exp ession o c I and he egula o y
ope on ca QRS. Ca S coun e ac s ep ession o P
B
by Ca A, leading o he
exp ession o he s uc u al ope on ca B, which is esponsible, along wi h
he gene p oduc o c I, o he syn hesis o ca o enoids. The ca o eno-
genesis induc ion by coppe is Ca F-independen , bu gene ic s udies ha e
demons a ed ha he genes esponsible o he syn hesis o ca o enoids
a e he same. A ows indica e posi i e egula ion; blun -ended lines indica e
nega i e egula ion. See ex o de ails.
Mini e iew Me allomics
Downloaded om h ps://academic.oup.com/me allomics/a icle/10/7/876/5952465 by Uni e sidad de G anada - Biblio eca use on 31 July 2025
884 |Me allomics, 2018, 10, 876--886 This jou nal is ©The Royal Socie y o Chemis y 2018
p oduc could unc ion as an al e na i e Cox subuni ha
p omo es M. xan hus i ness in he p esence o coppe . Those
esul s would explain why his me al induces ca o enogenesis
only in subop imal g ow h condi ions. This in e connec ion
be ween he ca o enogenesis esponse and cu A again e eals
he complexi y o he adap a ion mechanisms o coppe in
M. xan hus.
The hi d ques ion ha a ises is why non-ca o enogenic
mu an s a e as esis an (o e en mo e esis an ) o coppe as
he wild- ype s ain. This sugges s ha he syn hesis o ca o e-
noids i sel does no con ibu e o coppe ole ance in M. xan hus,
in spi e o he ac ha he abili y o he ca o enoids o a enua e
coppe -induced oxida i e damage has been clea ly demon-
s a ed.
53
Howe e , ano he easible explana ion could be ha
he absence o ca o enoids o e s imula es he exp ession o
some o he mechanisms in ol ed in coppe ole ance. The
in e dependence be ween diffe en sys ems is well documen ed
in he case o high up- egula ion o copA in a DcopB mu an o
o cus2 and cus3 sys ems in he double mu an DcopA–DcopB.
18
In his la e case, he mo e han 10- and 3- old inc ease in he
exp ession o Cus2 and Cus3 espec i ely no only compensa es
o he de iciency o he wo ATPases, bu i also yields a mu an
s ain ha is mo e esis an o coppe han he wild- ype
s ain.
18
Concluding ema ks and u u e
pe spec i es
The complex coppe esponse o M. xan hus in ol es he
pa icipa ion o many genes, se e al o which a e pa alogs, ha
a e inely con olled by diffe en egula o y elemen s ha sense
coppe in he cy oplasm o he pe iplasm and a e able o
diffe en ia e be ween he wo edox s a es o coppe o ac in
a ime-dependen manne . So a , only wo egula o y elemen s,
Co E and Co SR, ha e been iden i ied and cha ac e ized.
Howe e , aking in o conside a ion ha cus2,cus3 and cuoC
a e up- egula ed by coppe , bu a e no unde he con ol o
ei he o he wo iden i ied elemen s, and ha cuoC is no only
up- egula ed by coppe , bu also by s a a ion, he e is e idence
ha a leas wo o he ansc ip ional egula o s mus pa icipa e
in his complex esponse.
One in iguing ques ion is why M. xan hus encodes such a
high numbe o genes in ol ed in con e ing coppe ole ance
when i is no especially esis an o coppe . I is emp ing o
specula e ha such a high numbe o coppe -de oxi ica ion
sys ems could be necessa y o success ully comple e he mul i-
cellula li es yle o his bac e ium. Se e al da a, such as he ac
ha g owing and de eloping cells show diffe en coppe sensi-
i i ies and ha de ec s in agg ega ion and spo ula ion a e
obse ed in some mu an s, indica e ha se e al o hese
elemen s a e equi ed o no mal de elopmen in an en i on-
men whe e coppe may be abundan . Ne e heless, i canno
be uled ou ha M. xan hus may also use some o hese
elemen s du ing g ow h when cells p ey on some o he mic o-
o ganisms, in he same way ha euka yo ic p eda o s and
mac ophage do.
54–56
This is an in e es ing ques ion ha needs o
be add essed. In summa y, all o hese answe ed and unanswe ed
ques ions indica e ha M. xan hus’ coppe esponse is ca ied ou
by a ne wo k o in e connec ed mechanisms ha a e p ecisely
egula ed by unique elemen s. Un a eling his angle o p o eins
used by M. xan hus o adap he di e en cell ypes o changing
en i onmen s will con ibu e o ou unde s anding o coppe
signaling in li ing cells.
Con lic s o in e es
The e a e no con lic s o decla e.
Acknowledgemen s
This wo k has been suppo ed by he Spanish Go e nmen ,
g an s CSD2009-00006 and BFU2012-33248 o Jose
´Mun
˜oz-
Do ado, and BFU2016-75425-P o Au elio Mo aleda-Mun
˜oz
(70% unded by FEDER). We would like o hank Sil ia A ian
and Me ce
`Capde illa o con ibu ing o Co E me al binding
s udies (unpublished).
Re e ences
1 C. Rensing and S. F. McDe i , The coppe me allome in
p oka yo ic cells, Me . Ions Li e Sci., 2013, 12, 417–450.
2 S. Chillappaga i, A. Seube , H. T ip, O. P. Kuipe s,
M. A. Ma ahiel and M. Mie hke, Coppe s ess affec s i on
homeos asis by des abilizing i on-sul u clus e o ma ion
in Bacillus sub ilis,J. Bac e iol., 2010, 192, 2512–2524.
3 L. Macombe and J. A. Imlay, The i on-sul u clus e s o
dehyd a ases a e p ima y in acellula a ge s o coppe
oxici y, P oc. Na l. Acad. Sci. U. S. A., 2009, 106, 8344–8349.
4 K. J. Wald on, J. C. Ru he o d, D. Fo d and N. J. Robinson,
Me allop o eins and me al sensing, Na u e, 2009, 460,
823–830.
5 P. Chand angsu, C. Rensing and J. D. Helmann, Me al
homeos asis and esis ance in bac e ia, Na . Re . Mic obiol.,
2017, 15, 338–350.
6 R. A. Fes a and D. J. Thiele, Coppe : an essen ial me al in
biology, Cu . Biol., 2011, 21, 877–883.
7 J. M. A gu
¨ello, D. Raimunda and M. Gonza
´lez-Gue e o,
Me al anspo ac oss biomemb anes: eme ging models o
a dis inc chemis y, J. Biol. Chem., 2012, 287, 13510–13517.
8 D. H. Nies, Efflux-media ed hea y me al esis ance in
p oka yo es, FEMS Mic obiol. Re ., 2003, 27, 313–339.
9 J. A. Delma , C. C. Su and E. W. Yu, Bac e ial mul id ug
efflux anspo e s, Annu. Re . Biophys., 2014, 43, 93–117.
10 K. J. Wald on and N. J. Robinson, How do bac e ial cells
ensu e ha me allop o eins ge he co ec me al?, Na . Re .
Mic obiol., 2009, 6, 25–35.
11 C. Rademache and B. Masepohl, Coppe - esponsi e gene
egula ion in bac e ia, Mic obiology, 2012, 158, 2451–2464.
12 P. Cao, A. Dey, C. N. Vassallo and D. Wall, How myxobac e ia
coope a e, J. Mol. Biol., 2015, 427, 3709–3721.
Me allomics Mini e iew
Downloaded om h ps://academic.oup.com/me allomics/a icle/10/7/876/5952465 by Uni e sidad de G anada - Biblio eca use on 31 July 2025
