Biology Reference
In-Depth Information
of PerR-regulated genes involved in nitrogen metabolism (
nrtA
and
nirA
),
photosynthesis (
ccmL
,
ccmM
, and
ccmN
) and nutrient transport (
pstB
and
pstC
homologues) among other functional categories (
Kobayashi et al., 2004
).
However, some of these results also showed that many genes responding to
oxidative stress are PerR independent, indicating that Slr1738/PerR is not
the only regulator of the concerted response to peroxide stress in
Synecho-
cystis
(
Li et al., 2004
; Kobayashi et al., 2004).
Concerning
Anabaena
PCC 7120, neither FurB nor FurC seem to func-
tion as PerR orthologues, pointing to FurA as a dual responsive regulator
that participates in the control of iron metabolism and the oxidative stress
response. The pathway leading to induction of the peroxide stimulon is not
yet well understood in cyanobacteria. Disruption of cellular homeostasis by
other environmental stresses lead to enhanced generation of ROS that could
act as a cellular signal or be a part of a systemic response. Under adverse
conditions, the cyanobacterial transcriptome is reprogrammed to allow an
optimal cellular co-ordination (
Singh et al., 2010
) and PerR has been found
among the commonly regulated genes under most perturbations.
3.1.2.3. FurB from
Anabaena
: a moonlighting protein?
FurB orthologues are present in almost all cyanobacteria except cyano-
bacterium UCYNA. Although most cyanobacteria contain a single
furB
gene,
A. marina
MBIC11017 genome harbours four homologues, two of
them encoded by a plasmid and some
Cyanothece
strains possess two
furB
homologues. In contrast to FurA proteins, the
furB
orthologues in
Synecho-
cystis
PCC 6803 (
sll1937
) and
Anabaena
PCC 7120 (
all2473
) are dispensable
under standard culture conditions (
Kunert et al., 2003
;
Napolitano et al.,
2012
). In
Synechocystis
PCC 6803,
sll1937/furB
seems not to be involved in
the control of the
isiAB
operon (
Kunert et al., 2003
) and the constitutive
expression of the Zn
2+
uptake transporter operon
znuCAB
in the
sll1937
-
inactivated mutant strongly suggests that Sll1937 works as a Zur protein in
this cyanobacteria (
Pakrasi, Ogawa, & Bhattacharrya-Pakrasi, 2004
).
In
Anabaena
PCC 7120, it has been suggested that FurB, the product
of
all2473
, may protect cells against oxidative stress, most likely by direct
protection of the cyanobacterial nucleoid, in a similar way to a Dps protein
(
López-Gomollón et al., 2009
). This hypothesis is based on the fact that
expression of the gene is strongly induced under oxidative challenge and
its overexpression in
E. coli
increases its tolerance to H
2
O
2
and paraquat.
In addition, FurB presents a very high isoelectric point (pI 8.7), similar
to histones, and protects DNA in vitro from ROS and DNaseI damage.
