Handling Copper: A Paradigm for the Mechanisms of Metal Ion Homeostasis - Environmental Contamination: Health Risks and Ecological Restoration - page 270

FIGURE 13.2
Ribbon. model. of. an. ATX-like. copper. chaperone. depicting. a.
typical. βαββαβ. (ferredoxin-like). fold.. Model. was. made. using.
SWISS-MODEL. and. DeepView/Swiss-PbdViewer. software..
(Guex,. N.. and. Peitsch,. M.C.,. Electrophoresis ,. 18,. 2714,. 1997;.
Peitsch,. M.C.,. Bio/Technology ,. 13,. 658,. 1995;. Schwede,. T.. et. al.,.
Nucl. Acids Res .,.31,.3381,.2003.)
chaperones.from.this.point.forward).are.small,.low.molecular.weight,.intra-
cellular. proteins. that. carry. Cu(I). (or. other. metal. ions). from. one. target. to.
another.(Harrison.and.Dameron.1999)..It.is.believed.that.copper.chaperones.
are. highly. target-speciic,. always. traficking. Cu(I). to. and. from. particular.
proteins. (O'Halloran. and. Culotta. 2000).. The. crystal. structure. of. the. yeast.
ATX1. (Antioxidant1). chaperone. shows. a. βαββαβ. (ferredoxin-like). fold. that.
is.a.conserved.pattern.among.ATX1.homologs.as.well.as.some.other.copper.
homeostasis. proteins. including. P 1B -type. ATPase. transporters. (Figure. 13.2).
(Rosenzweig. et. al.. 1999,. Rosenzweig. and. O'Halloran. 2000).. Most. ATX-like.
copper. chaperones. contain. a. putative. metal. binding. motif,. CxxC,. near. or.
in. the. irst. alpha. helix. (Pufahl. et. al.. 1997,. Huffman. and. O'Halloran. 2001)..
Another. type.of.copper. chaperone. is.the. CCS. protein. that.has. been. found.
in. yeast,. insects,. plants,. and. humans. that. functions.to. transport. copper. to.
cellular. SOD. enzymes. (Culotta. et. al.. 1997,. 2006).. Crystallographic. struc-
ture.analyses.of.CCS.proteins.indicate.that.it.consists.of.three.domains:.an.
ATX-like.domain.(domain.I),.a.SOD-like.domain.(domain.II),.and.a.unique.
domain.(domain.III).(Lamb.et.al..1999,.2000,.Hall.et.al..2000)..A.CxxC.metal.
binding.sequence.is.present.in.the.amino.terminal,.ATX-like.domain.of.this.
copper.traficking.protein.(Lamb.et.al..1999).
The.third.major.group.of.copper.homeostasis.proteins.is.metallothioneins.
which.are.small,.cysteine-rich.proteins.that.have.been.found.in.a.variety.of.
different. organisms.. Even. though. these. proteins. are. relatively. small. their.
sequence. can. contain. up. to. 30%. cysteine. residues. (Kagi. et. al.. 1979).. Some.
metallothioneins. are. able. to. bind. approximately. 12. copper. ions,. 6. in. the. β.
domain. and. 6. in. the. α. domain. (Nielson. and. Winge. 1984).. With. this. high.
binding.capacity.for.copper,.metallothioneins.have.the.potential.to.sequester.
a. large. amount. of. excess. metal. in. the. cell.. Arabidopsis . contains. four. genes.
encoding. metallothioneins. that. comprise. two. groups. classiied. based. on.
their.structure,.MT1.and.MT2.(Zhou.and.Goldsbrough.1994)..There.is.some.
evidence.that.increased.mRNA.levels.of.MT2.are.correlated.with.copper.tol-
erance.in.some.ecotypes.of. Arabidopsis .(Murphy.and.Taiz.1995)..Experimental.
data,.using.GUS.fusion.analysis,.suggest.that.metallothioneins.in. Arabidopsis .
have.speciic.function..The.gene.promoters,. MT1a .and. MT2b ,.are.involved.in.