Biology Reference
In-Depth Information
the signal transduction will occur with the same mechanism (
Ayers &
Moffat, 2008; Hao et al., 2002; Key & Moffat, 2005
).
2.2.2.2 The Vibrio vulnificus and the Chromobacterium violaceum globin-
coupled regulators (VvGReg and CvGReg)
To date, only two GCSs have been identified to control gene expression by
protein-protein interaction. The first member of this category was identified
by Freitas and coworkers in 2003 in the Gram-negative
d
-Proteobacterium
V. vulnificus
genome (
Freitas et al., 2003
), and the second member was iden-
tified in 2005 in the
d
-Proteobacterium
C. violaceum
(
Freitas et al., 2005
).
These sensors are characterized by the fusion of an N-terminal globin-like
domain to a C-terminal STAS domain (sulphate transporter and anti-anti-
sigma factor) (
Campbell, Westblade, & Darst, 2008
). Therefore, the tran-
scription control played by
Vv
GReg and
Cv
GReg involves the indirect
stimulation of bacterial RNAP by inactivating the inhibitory anti
s
-kinases,
similar to what happens in stressosomes of
B. subtilis
(see
Section 2.5.1
). This
causes the liberation of
s
factors that direct the specific transcription of target
genes or operons.
Only a few crystal structures of STAS domains are known (
Marles-
Wright et al., 2008; Quin et al., 2012
). It is clear that, despite evolutionary
distances in the amino acid sequence, all these structures display a conserved
fold that comprises four
b
-strands interspersed among five
a
-helices.
2.2.2.3 The globin-coupled HK from Anaeromyxobacter sp. strain Fw109-5
(AfGcHK)
In
Anaeromyxobacter
sp. strain Fw109-5, the first example of a globin domain
coupled to an HK has been identified, namely,
Af
GcHK (
Kitanishi
et al., 2011
).
The globin domain of
Af
GcHK displays significant homology to the
Sw
Mb (16% identity and 34% similarity) and to the HemAT-
Bs
(24% iden-
tity and 39% similarity). The UV-vis characterization is in-line with the clas-
sical spectra of haem-binding globins. RR measurements revealed the
presence of a histidine residue (His99) at the proximal side and of a tyrosine
residue (Tyr45) at the distal side. Tyr45 is also important for the stabilization
of the exogenous ligand.
The HK domain shows one autophosphorylation site (His183) and two
phosphorylation sites (Asp52 and Asp169). The presence of a low-spin
Fe(III), Fe(II)-O
2
, or Fe(II)-CO activates the kinase activity, where the
high-spin Fe(II) is the inactive form (
Kitanishi et al., 2011
).
