Biology Reference
In-Depth Information
2.5.2 The non-haem-coupled regulator from Moorella thermoacetica
and the non-haem-coupled sporulation inhibitory proteins from
Bacillus anthracis
The
M. thermoacetica
stressosome, which regulates the biosynthesis of
c-di-GMP, has been recently characterized and comprises two components,
non-haem-coupled regulator from
M. thermoacetica
(MtR) and MtS. MtR
N-terminal domain has been identified as structurally homologous to
B. subtilis
RsbR despite low sequence identity (12%), as such being a
non-haem globin (
Quin et al., 2012
). As for
B. subtilis
, the stress response
mechanism in
M. thermoacetica
remains unknown.
Non-haem-coupled sporulation inhibitory proteins from
B. anthracis
(pXO1-118 and pXO2-61) are two sporulation inhibitory proteins identi-
fied in
B. anthracis
and are non-haem globins (
Stranzl et al., 2011
). Instead of
the haem group, they bind fatty acids in a hydrophobic tunnel and a hydro-
philic chamber. It has been suggested that this kind of non-haem globin
senses changes in intracellular fatty acid composition, chloride concentra-
tion, and/or pH, thus modulating the sporulation rate of the organism
(
Stranzl et al., 2011
).
3. THE EVOLUTION OF THE GLOBINS
Extensive analyses of the sequences of globins and putative globins
have been carried out regularly in the past years in parallel with the constant
growth of new genome annotation. Hypotheses on the evolution of single
domain and chimeric globins, as well as on the development of functional
specializations, have always been proposed and debated (
Blank & Burmester,
2012; Freitas et al., 2004; Vinogradov et al., 2007
).
As globins are found in all kingdoms of life, it seems to be logical that the
ancestor of all globins was present in the first organisms populating the Earth,
the Last Universal Common Ancestor (LUCA) some 4000 Myr (
Freitas
et al., 2004; Moens et al., 1996; Vinogradov et al., 2007
). Although the envi-
ronmental oxygen amount was very low at that time (
<
0.0008 atm), high
local concentration might have been present, thus being lethal for anaerobic
organisms and causing oxidative stress. Under these conditions, the evolu-
tion of globins started and it has been postulated that their initial role was
NO-detoxification (
Poole, 2005; Poole & Hughes, 2000
). Only at a later
stage, they evolved into the multi-domain sensors as we know them to date.
Phylogenetic analyses show that the globin sequences appear to be dis-
tributed into three separate lineages, (i) the 3/3 globins of plants and
