Biology Reference
In-Depth Information
ManS contains a histidine kinase domain in the C-terminal region
that includes a phosphorylatable His residue, and two membrane-spanning
domains in the N-terminal region. It has been proposed that the region
between these two membrane-spanning domains is located in the peri-
plasmic space and perceives the extracellular concentration of Mn
2+
ions
by providing ligands to Mn
2+
(
Yamaguchi et al., 2002
). The transcrip-
tional response regulator ManR belongs to the OmpR/PhoB subfamily
(
Martinez-Hackert & Stock, 1997
) and contains two functional domains,
an N-terminal phosphorylation domain, which includes a phosphorylat-
able Asp residue that receives the signal of ManS, and a C-terminal DNA-
binding domain. Punctual mutation of either the His-205 residue of the
manS
gene or the Asp-52 residue of the
manR
gene induces the expres-
sion of the
mntABC
operon, suggesting that both residues are essential for
the transduction of Mn
2+
signals. Even though unphosphorylated ManR
is bound to the promoter regions of
mntABC
in vitro, transcription seems
to be repressed only by its phosphorylated form (
Yamaguchi et al., 2002
).
In
Anabaena
PCC 7120, the ManS/ManR two-component system mod-
ulates the expression of genes
all3575
,
all3574
and
alr3576
that encode the
homologous proteins of MntABC from
Synechocystis
PCC 6803 (
Huang &
Wu, 2004b
). Besides, this two component Mn
2+
-sensing system controls the
expression of the natural resistance-associated macrophage protein (Nramp)
homologous MntH (
Huang & Wu, 2004a
), another type of bacterial Mn
2+
transporter that is widespread throughout diverse groups of eubacteria
(
Jakubovics & Jenkinson, 2001
).
The transcriptional metallorepressor ManR is specifically bound to the
Anabaena
sp.
mntH
promoter through a DNA sequence of 19 bp com-
posed of two direct repeats in the form of (T/A)ATGA(G/A)A(A/G)
separated by 3 bp, which appears highly conserved in the promoter regions
of genes encoding MntABC and MntH homologues of several cyanobac-
teria (
Huang & Wu, 2004a
). Since this two direct repeats arrangement is
typical of DNA recognition motifs from OmpR/PhoB response regulators
(
Okamura, Hanaoka, Nagadoi, Makino, & Nishimura, 2000
), the conserva-
tive consensus sequence (T/A)ATGA(G/A)A(A/G) recognized by ManR
appears as a novel regulatory DNA motif in cyanobacteria. The binding
of ManR to its target promoters occurs through the C-terminal HTH
domain, which contains at least three highly conservative amino acids resi-
dues among the OmpR/PhoB subfamily regulators that are essential for
DNA-binding activity (
Huang, Wu, Li, & Liu, 2006
). In vitro analyses sug-
gest that two ManR molecules cooperatively bind to the DNA recognition
