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fructose-1,6-bisphosphatase, pyruvate dehydrogenase, glyceraldehyde-3-
phosphate dehydrogenase, phosphoribulokinase, ribulose bisphosphate car-
boxylase, GDP-mannose 4,6-dehydratase, transketolase), and protection
against oxidative stress (1-Cys peroxiredoxin).
All cyanobacteria possess two types of Grx enzymes harbouring either
a CxxC- or a CGFS-type redox sites (
Table 5.2
). The CxxC Grxs have
been studied in various prokaryotes and eukaryotes organisms (
Herrero,
Belli, & Casa, 2010
;
Lillig et al., 2008
;
Masip et al., 2006
;
Rouhier et al.,
2008
; ). They catalyse the reduction of both protein disulfides (protein-
S-S-protein) and glutathione mixed disulfide (protein-S-SG) by a dithiol
or a monothiol mechanism. In the dithiol mechanism, the N-terminal
active site cysteine resolves the disulfide, or the protein-S-SG mixed disul-
fide of the glutathionylated proteins. Then, the oxidized cysteine of the
Grx enzyme is reduced by its second active site cysteine, itself subsequently
reduced by the NTR or FTR enzymes (
Zaffagnini, Bedhomme, Lemaire
et al., 2012
). In the monothiol mechanism, after its oxidation, the Grx
active site cysteine is subsequently reduced by GSH. Several laboratories
have analysed the two CxxC Grxs of the model cyanobacterium
Syn-
echocystis
PCC 6803, Grx1 (Slr1562 in Cyanobase) and Grx2 (Ssr2061),
which share the conserved CPFC redox motif driving the thiol oxidore-
ductase activity (
Li, Huang, Yang, Liu, & Wu, 2005
;
Marteyn et al., 2009
).
Grx2 serves as an electron donor to the arsenate reductase enzyme that
catalyses the detoxification of arsenate that is frequently encountered in
cyanobacterial biotopes (
Kim et al., 2012
). Furthermore, a Grx2 monothiol
mutant was used to capture 42 prey proteins operating in carbon metabo-
lism, protein synthesis and folding, light harvesting and protection against
oxidative stress (
Li et al., 2007
). Interestingly, 13 of these Grx2 target pro-
teins, including the catalase-peroxidase and a peroxyredoxin, were also cap-
tured by a Trx monothiol mutant (
Florencio et al., 2006
), emphasizing on
the cross-talk between the Grx and Trx enzymes. Also interestingly, we
found that both Grx1 and Grx2 operate in a novel integrative redox path-
way, NTR-Grx1-Grx2-Fed7 (Fed7 stands for ferredoxin 7), which pro-
tects
Synechocystis
PCC 6803 against selenate, another frequent pollutant
(
Marteyn et al., 2009
). Furthermore, we showed that under selenate stress,
Grx1 and Grx2 assemble under the form of a heterodimer. It will be inter-
esting to investigate further the influence of environmental conditions on
the possible formation of homo/heterodimers of Grx1 and Grx2 since
their counterpart in noncyanobacterial organisms can form dimers bridged
by a GSH-ligated 2Fe-2S cluster, which regulates the thiol oxidoreductase
