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activity and operates in oxidative-stress sensing (
Lillig et al., 2008
;
Rouhier,
Couturier, Johnson, & Jacquot, 2010
).
We have initiated the analysis of the single CGFS-type Grx, which is
present in all cyanobacteria (
Table 5.2
). We showed that the enzyme (Grx3)
of
Synechocystis
PCC 6803 forms a homodimer bridged by a GSH-ligated
2Fe-2S cluster, and that this feature is conserved in the orthologous enzymes
from bacteria, cyanobacteria, yeast, plants and mammals (
Iwema et al., 2009
;
Picciocchi, Saguez, Boussac, Cassier-Chauvat, & Chauvat, 2007
). This find-
ing was confirmed by several groups (
Herrero et al., 2010
;
Lillig et al., 2008
;
Rouhier et al., 2010
), and one of these Grxs was showed to be able to
transfer its GSH-anchored 2Fe-2S centre to the apoform of a 2Fe-2S fer-
redoxin (
Rouhier et al., 2010
). These results are important as iron-sulphur
centres play a crucial role in the electron transfers associated with photo-
synthesis, respiration and carbon metabolism (
Lillig et al., 2008
;
Rouhier
et al., 2010
). CGFS Grxs can also interact with the widely conserved BolA
protein family. In yeast, it has been shown that the interactions between
Grx3 or Grx4 with the BolA-like protein Fra2 operate in iron regulation
mediated by the Aft1 and Aft2 transcriptional regulators. These heterodi-
meric complex BolA-Grx possesses a (2Fe-2S) cluster ligated by a histidine
from Fra2, a cysteine from either Grx3 or Grx4, and the cysteine from GSH.
Similar findings were observed with the corresponding human proteins (
Li,
Mapolelo, Randeniya, Johnson, & Outten, 2012
), thereby establishing the
ubiquitous CGFS Grxs and BolA-like proteins as a novel type of 2Fe-2S
cluster binding regulatory complex. Further investigations are required to
determine whether the BolA-like and CGFS Grx proteins of cyanobacteria
can also assemble as a heterodimer bridged by a GSH-ligated 2Fe-2S cluster
operating in iron regulation which is vital to cyanobacteria (
Houot et al.,
2007
;
Shcolnick et al., 2009
).
6. CONCLUDING REMARKS
It is important to analyse the defences against oxidative stress in cya-
nobacteria because they are the organisms that developed most of these
mechanisms as a crucial necessity to cope with the production of ROS
by their active photoautotrophic metabolism, which supports a large part
of the biosphere and has valuable biotechnological potentials. Further-
more, many of the effective anti-oxidant processes that likely emerged in
cyanobacteria have been conserved, and complexified in higher plants
and mammals.
