Biology Reference
In-Depth Information
Pesavento & Hengge, 2009; R¨mling & Amikam, 2006; R¨mling et al.,
2005; Tamayo et al., 2007
). DGC contains the GGDEF domain, named
from the conserved sequence motif (Gly-Gly-Asp-Glu-Phe) that constitutes
part of the active site of the enzymes (
Karatan &Watnick, 2009
). Formation
of cyclic di-GMP is catalysed by two GGDEF domains with two GTP (gua-
nosine triphosphate) molecules. PDE catalyses hydrolysis of cyclic di-GMP
to the linear form 5
0
-pGpG.
The GGDEF domain is typically found coupled to a variety of other sensor
and/or regulator domains including PAS and globin domains within
multi-domain proteins (
Jenal, 2004; R¨mling & Amikam, 2006
). It is ex-
pected that these sensor and regulator domains will be responsible for receiv-
ing directly or indirectly the extracellular signal to regulate the DGC activity.
A haem-containing sensor domain is adopted in several DGC and PDE
including HemDGC,
Bpe
GReg, YddV (
Ec
DosC),
Ec
Dos, and
Ax
PDEA.
HemDGC,
Bpe
GReg, and YddV belong to the globin-coupled sensor
proteins, which consists of globin and GGDEF domains. HemDGC from
Desulfotalea psychrophila
shows the DGC activity only when O
2
is bound
to the haem (
Sawai et al., 2009
). Though HemDGC also binds CO and
NO, CO- and NO-bound HemDGCs show no enzymatic activity
(
Sawai et al., 2009
). Neither ferric nor ferrous HaemDGC shows the
DGC activity. Mutagenesis and resonance Raman studies reveal that the
ligand discrimination is achieved by changing a hydrogen-bonding network
between the haem-bound ligand and surrounding amino acid residues in the
distal haem pocket. In the O
2
-bound form, the hydrogen-bonding network
is formed among the haem-bound O
2
, Tyr55, and Gln81, while only Gln81
is interacting with the haem-bound CO in the CO-bound form (
Sawai
et al., 2009
).
The DGC activity of
Bpe
GReg (globin-coupled DGC from
Bordetella per-
tussis
) is also activated by 10-fold uponO
2
binding to the haem comparedwith
that of the ferrous form (
Wan et al., 2009
). Unlike HemDGC,
Bpe
GReg
shows the DGC activity in the NO- and CO-bound forms though their
activity is lower than that of the O
2
-bound form (
Wan et al., 2009
). Phe-
notype analyses reveal that
Bpe
GReg is involved in the regulation of biofilm
formation (
Wan et al., 2009
). A homologue of
Bpe
GReg found in
Azotobacter
vinelandii
,
Av
GReg, is purified and studied by resonance Raman spectroscopy
for the haem environmental structure (
Thijs et al., 2007
).
The
yddV
(
dosC
) gene is a part of the operon encoding the
Ecdos
gene, and
these two genes are co-transcribed (
Tuckermanetal.,2009
). The gene prod-
ucts, YddV (DosC) and
Ec
Dos, are suggested to form an associated complex
