Biology Reference
In-Depth Information
A study of the single DPS protein of
Synechocystis
PCC 6803 (MrgA)
demonstrated a reduction in the ability of Δ
mrgA
cells to withstand expo-
sure to hydrogen peroxide (
Li, Singh, McIntyre, & Sherman, 2004
). In
addition, MrgA was found to have an important role in iron homeo-
stasis. Δ
mrgA
cells grew much slower than wild-type cells when trans-
ferred from iron-sufficient to iron-deficient conditions, such as the BFR
mutants (
Shcolnick et al., 2007
). However, unlike the BFR mutants, the
internal iron quota of Δ
mrgA
cells grown on sufficient iron was similar
to that of wild-type cells (Shcolnick et al., 2007). An examination of an
array of mutants in both bacterioferritin and DPS genes demonstrates a
connection between internal iron quota, the presence of the two stor-
age complexes and the sensitivity to externally applied oxidative stress
(Scholnick et al., 2009). Bacterioferritins function as the main storage
complexes, whereas DPS-type proteins function downstream in the iron
storage pathway, releasing iron from bacterioferritins and transporting it
towards its final destination. The combined action of the two complexes
allows safe accumulation and release of iron from storage by minimiz-
ing damage resulting from interactions between free iron and the oxygen
radicals that are produced in abundance by the photosynthetic apparatus
(Scholnick et al., 2009).
Peña and Bullerjahn (1995)
and
Peña, Burkhart, and Bullerjahn (1995)
isolated and studied the DPS protein of
Synechococcus
sp. PCC 7942. The
genome of this organism codes for one bacterioferritin and one DPS pro-
tein. The DPS protein forms large complexes (approximately 150 kDa) and
possesses both ferroxidase and catalase activity. The authors also report on
binding to chromosomal DNA, which may contribute to local protection
against oxidative damage. DNA binding was also reported by
Franceschini,
Ceci, Alaleona, Chiancone, and Ilari (2006)
for the DPS protein from
Ther-
mosynechococcus elongatus
. Interestingly, the
Synechococcus
DPS exhibits a high
degree of homology to bacterioferritins and, indeed, binds haeme (
Peña &
Bullerjahn, 1995
). The transcription of this protein is induced by iron limita-
tion (
Sen, Dwivedi, Rice, & Bullerjahn, 2000
). A very similar protein was iso-
lated from
Trichodesmium erythraeum
(
Castruita et al., 2006
). However, haeme
binding was not reported for this protein. The transcript coding for this pro-
tein was found to be induced under nitrogen limitation, which should not
be surprising when the iron requirement of the nitrogenase is considered
(
Sandh et al., 2011
). In the
furA
overexpressing mutant of
Anabaena
sp. PCC
7120, the expression of
dpsA
was enhanced, suggesting regulation by the Fur
system (
Hernández, Pellicer, Huang, Peleato, & Fillat, 2007
). This protein
