Biology Reference
In-Depth Information
The cognate response regulator, which is activated by
Af
GcHK-
mediated phosphorylation, has been identified (
Anae109_2439
). Pho-
sphotransfer reactions have been performed
in vitro
and occur as early as
5 min after ATP addition to the reaction mixture (
Kitanishi et al., 2011
).
2.2.3 Regulation of gene expression via second messenger biosynthesis
Cyclic dimeric-(3
0
-5
0
)-GMP (c-di-GMP) was initially discovered in
Gluconacetobacter xylinus
(previously named
Acetobacter xylinum
) where it reg-
ulates cellulose synthesis (
Ross et al., 1987
). A number of other bacterial
functions have been progressively ascribed as controlled by c-di-GMP, that
is, biofilm formation, motility, virulence, and the cell cycle (
Abel et al.,
2011; Bobrov et al., 2011; Duerig et al., 2009; Karaolis et al., 2005;
Kulasakara et al., 2006; Ryan et al., 2007, 2010; Tamayo, Pratt, &
Camilli, 2007; Tischler & Camilli, 2004
), promoting it as a universal bacte-
rial second messenger.
The biosynthesis and the degradation of c-di-GMP are executed by two
enzymes, the DGC and the PDE, respectively. Highly conserved motifs can
be recognized in these proteins, that is, the GGDEF motif in DGC and the
EAL motif in PDE (
Ausmees et al., 2001; Matilla, Travieso, Ramos, &
Ramos-Gonzalez, 2011; Simm, Morr, Kader, Nimtz, & Romling, 2004
).
Most commonly, enzymes with GGDEF and EAL motifs combine the
catalytically active domain with a sensor domain. The sensor domain recog-
nizes specific environmental signals, such as the gas concentration, redox
state of the electron transport chain, light quorum-sensing, and many others,
regulating the synthesis or the degradation of c-di-GMP (
Deng et al., 2012;
Henry & Crosson, 2011; Ho, Burden, & Hurley, 2000
).
2.2.3.1 The direct oxygen sensor from E. coli (EcDos)
The
E. coli
direct O
2
sensor (
Ec
Dos) is expressed via transcription and trans-
lation of an operon (
dosCP
). The
dosCP
operon codes for two proteins, one
includes a haem-binding PAS domain coupled to a C-terminal PDE domain
(
Ec
DosP), the second comprises a globin domain coupled to a DGC domain
(
Ec
DosC) (
Delgado-Nixon et al., 2000; Tuckerman et al., 2009
).
Ec
DosP is a chimeric protein that shows high-sequence homology
between its N-terminal region and the PAS domain of rhizobial FixL
(25% identity and 60% similarity) (
Blattner et al., 1997
) and between its
full-length sequence and the
G. xylinus
PDE (30% identity and 50% simi-
larity) (
Delgado-Nixon et al., 2000
). Spectroscopic analysis on the purified
Ec
DosP identifies a low-spin hexa-coordinated ferric-haem complex with
