Biology Reference
In-Depth Information
for the non-haeme-containing ferritin in
Helicobacter pylori
(
Delany, Spohn,
Rappuoli, & Scarlato, 2001
). Recently, a fourth mode of Fur action was dis-
covered by which the expression of the major iron storage protein of
E. coli
,
FtnA, is regulated. In this case, repression of expression is manifested by the
histone-like nucleoid-associated protein H-NS, which binds to the pro-
moter region. H-NS is displaced by association of iron-loaded Fur, which
enables binding of RNA polymerases (
Nandal et al., 2010
). Thus, multiple
modes of Fur-dependant expression regulation exist, which all depend on
the structural change of the protein upon iron interaction.
Fur proteins exist in cyanobacteria and have been described in, e.g.
Syn-
echococcus
sp. PCC 7942 (
Ghassemian & Straus, 1996
),
Anabaena
sp. PCC
7119 (
Bes et al., 2001
),
Synechocystis
sp. PCC 6803 (
Kunert, Vinnemeier,
Erdmann, & Hagemann, 2003
) and
Microcystis aeruginosa
(
Martin-Luna, Her-
nandez, Bes, Fillat, & Peleato, 2006
). A Fur box can be identified in targeted
genes albeit with variable arrangement as compared to
E. coli
(
Hernández,
López-Gomollón et al., 2006
). Similar to the autoregulatory system in
E.
coli
, two putative Fur target sequences have been found upstream of the
fur
start codon, e.g. the
fur
gene of the filamentous cyanobacterium
Anabaena
sp. PCC 7119 (
Bes et al., 2001
). Thus, it can be concluded that the mode
by which Fur regulates cyanobacterial gene expression is similar to the pro-
teobacterial one.
Many cyanobacteria encode three Fur homologues. The interplay
between these factors was analysed in
Anabaena
sp. PCC 7120, where they
are termed FurA (
all1691
;
sll0567
in
Synechocystis
sp. PCC 6803), FurB
(
all2473
;
sll1937
in
Synechocystis
sp. PCC 6803) and FurC (
alr0957
; not yet
identified in
Synechocystis
sp. PCC 6803;
Hernández, López-Gomollon, Bes,
Fillat, & Peleato, 2004
;
Kaneko et al., 1996
). FurA is essential (
Hernández,
López-Gomollón et al., 2004
;
Hernández, Muro-Pastor et al., 2006
;
Kunert
et al., 2003
), shows the highest similarity to Fur from heterotrophic bacteria
and contains the characteristic HHXHXXCXXC motif. FurB contains a
cluster of three histidine residues, instead of the HHXHXXCXXC motif
(
Kunert et al., 2003
). In contrast to FurA, the function of FurB is not essential
(
Napolitano et al., 2012
). An additional Fur family regulator is PerR (slr1738),
usually thought of as a regulator of oxidative stress. However, in
Synechocys-
tis
sp. PCC 6803, this protein was found to play a role in iron homeostasis
(
Li et al., 2004
;
Shcolnick, Summerfield, Reytman, Sherman, & Keren, 2009
)
and in the response to heavy metals (
Houot et al., 2007
) as well.
