Biology Reference
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domains displays an active site for GTP binding and an inhibitory site for
c-di-GMP binding, and the molecule is represented as a homo-dimer
(
Wan et al., 2009
).
The capability of synthesizing c-di-GMP upon selective binding of O
2
,
as well as the dependence of biofilm formation on the
Bpe
GReg activity, has
been demonstrated (
Wan et al., 2009
).
Different states of the globin domain, bound or unbound, drive different
levels of DGC activity. When in the Fe(II)-O
2
state, the c-di-GMP synthe-
sis is at the highest level. This level decreases progressively in the presence of
Fe(II)-NO, Fe(II)-CO, and Fe(II) (
Wan et al., 2009
).
The presence of the predicted inhibitory site is confirmed by activity
assays performed in the absence and presence of a PDE, which sequesters
the newly synthesized c-di-GMP and converts it into pGpG. Without
PDE, the reaction catalysed by
Bpe
GReg slows down quickly and stops
before the GTP present is completely used. With PDE, the reaction pro-
ceeds to completion within minutes (
Wan et al., 2009
).
Bioinformatic analysis of the linker region sequence identifies a highly con-
served residue, His225.Mutations of this residue result in an interruption of the
c-di-GMP production, regardless of the haem-group state. On the other hand,
the globin domain absorption spectra are not affected by the mutation. These
data suggest that His225 is involved in the DCG activation (
Wan et al., 2009
).
B. pertussis
is a human pathogen capable of forming biofilms. The participa-
tion of
Bpe
GReg in the biofilm formation pathway has been investigated. The
comparison of
Bpe
GReg knock-out and wilde-type shows a much lower bio-
film presence in the first case, thus confirming the hypothesis (
Wan et al., 2009
).
2.2.3.4 The haem-containing diguanylate cyclase from Desulfotalea
psychrophila
A haem-containing diguanylate cyclase (HemDGC) is expressed in the
obligatory anaerobic bacterium
D. psychrophila
as a homo-tetramer (
Sawai
et al., 2010
).
HemDGC displays a globin domain coupled to a DGC and its activity is
stimulated upon binding of O
2
, probably recognized as a toxic molecule,
thus stimulating biofilm formation as a defence mechanism. For this reason,
HemDGC is probably involved in the protection of the bacterium against
oxidative stress.
RR spectra show that the haem axial ligands are His108 at the proximal
side and Tyr55-Gln81 (in presence of O
2
) or Gln81 (in presence of CO) at
the distal side. It is possible to suggest that the role of Tyr55 in the
