Biology Reference
In-Depth Information
genomes within members of the three globin families. In addition, a more
comprehensive nomenclature for both prokaryotic and eukaryotic globins
was proposed: the canonical 3/3 alpha-helical fold (the myoglobin (Mb)-
fold) includes two families: the Mb-like family containing both single-
domain haemoglobins (SDHbs) and flavohaemoglobins (FHbs) and the
sensor globin family enclosing protoglobins and single-domain sensor glo-
bins (SDSgb). The truncated Mb-fold family (T family) displays a 2/2 alpha-
helical fold (truncated Mb-fold) and contains truncated haemoglobins
(TrHb1, TrHb2 and TrHb3) (
Vinogradov et al., 2013
).
Despite the vast number of globins in bacteria, our understanding of their
physiological functions is restricted to only a few examples.
Table 4.1
sum-
marises the current understanding of
in vivo
function(s) and regulation of the
most extensively studied bacterial globins: the FHb of
Escherichia coli
(Hmp),
the single-domain globin of
Vitreoscilla
(Vgb), the truncated globins of
Myco-
bacterium tuberculosis
(HbN and HbO) and the single-domain (Cgb) and trun-
cated (Ctb) globins of
C. jejuni
. Resistance to nitrosative stress and
involvement in oxygen transfer are the most prevalent functions for bacterial
haemoglobins (see
Table 4.1
). However, given the number of bacterial
genomes that encode globin-like sequences (
1100) (
Vinogradov et al.,
2013
), the number of globins whereby functions have been elucidated via
the robust approach of mutation/complementation is very limited (
15).
C. jejuni
has been shown to be a good model for the analysis of globin
function. Indeed, (i) construction of mutants for both
cgb
and
ctb
has allowed
the inference of functions, (ii) the regulation of globin expression under
conditions of nitrosative stress has been extensively studied, (iii) purified glo-
bins have been subject to structural and kinetic characterisation and
(iv) heterologous expression, as a tool to explore function, has also been
exploited. However, many questions remain, pertaining to the physiological
function of the globins of
Campylobacter
(especially Ctb), and the potential
interaction between Cgb and Ctb is yet to be investigated. This review aims
to provide an overview of our current understanding of the globins of
C. jejuni
, including the impact of gene deletions on phenotype, transcrip-
tional regulation and the biochemical/biophysical/structural characterisa-
tion of Cgb and Ctb.
2. NO AND RNS IN BIOLOGY
NO is a free radical with an unpaired electron and readily reacts with a
variety of biological molecules
(
Halliwell & Gutteridge, 2007
). The
