Biology Reference
In-Depth Information
5. CAMPYLOBACTER SINGLE-DOMAIN GLOBIN, CGB:
FUNCTIONAL AND STRUCTURAL CHARACTERISATION
5.1. Functional characterisation
The presence of a globin-like sequence in
C. jejuni
NCTC 11168 (
Parkhill
et al., 2000
) (Cj1586) resembling that of the Vgb was reported for the first
time in 2001 (
Bollinger et al., 2001
). Since then, important progress has con-
tributed towards the characterisation of the physiological role, structural
characteristics and regulation of this haemoglobin, now known as Cgb
(for
Campylobacter
globin). Cgb is a member of the Mb-like haemoglobins,
belonging to the single-domain haemoglobin sub-family (SDHb)
(
Vinogradov et al., 2013
). Cgb, composed of 140 residues (16.1 kDa), shares
42% amino acid identity with the Vgb. Although Cgb lacks the reductase
domain present in the FHbs, it shares a high level of sequence homology
with the globin domains of FHbs from
Bacillus subtilis
,
Salmonella enterica
serovar Typhimurium and
E.
coli
(39%, 34% and 33%, respectively)
(
Elvers et al., 2004
).
The first evidence for the involvement of Cgb in resistance against
nitrosative stress came from a study aimed to measure the protection pro-
vided by the heterologous expression of several bacterial haemoglobins in
E. coli
(
Frey et al., 2002
). Cultures of Cgb-expressing cells showed a signif-
icant improvement in growth compared to the parental strain in the pres-
ence of sodium nitroprusside (SNP), a clinically relevant NO donor
(
Miller &Megson, 2007; Wang et al., 2002
). It is nowwell known that resis-
tance against NO and nitrosative stress agents is linked to the presence of
Cgb in
Campylobacter
. There are several studies that support this:
(i) growth of
C. jejuni
in the presence of the nitrosative agent
S
-nitrosoglutathione (GSNO) is impaired by mutation of
cgb
(
Avila-
Ramirez et al., 2013; Elvers et al., 2004
); (ii) tolerance to GSNO, SNP
and NO is significantly diminished in strains lacking
cgb
(
Elvers et al.,
2004; Wainwright et al., 2005
); (iii) Cgb consumes NO and protects aerobic
respiration of
C. jejuni
and
E. coli
from NO-mediated respiratory inhibition
(
Avila-Ramirez et al., 2013; Elvers et al., 2004; Monk et al., 2008
);
(iv) Colorectal adenocarcinoma cells infected with a
cgb
-defective strain
accumulate a higher concentration of NO than cells infected with the parent
strain or uninfected cells (
Elvers et al., 2004
) and (v) Cgb is a member of a
small regulon positively controlled by NssR under nitrosative stress condi-
tions (see
Section 7.1
), and the expression of
cgb
is triggered by GSNO, SNP,
