Biology Reference
In-Depth Information
importance in biological systems, and nowadays has an important role in
contemporary medicine, physiology, biochemistry and microbiology.
The behaviour of NO is made particularly complex by its ability to be
oxidised to the nitrosonium cation (NO
þ
) or reduced to the nitroxyl anion
(NO
) and to react with O
2
to form nitrite (NO
2
). Moreover, the reac-
tions of NO led to production of reactive nitrogen species (RNS) (reviewed
by
Bowman, McLean, Poole, & Fukuto, 2011; Poole & Hughes, 2000
),
such as ONOO
, formed by the reaction of NO with superoxide anion.
Extensive literature deals with NO and related species, especially
considering that NO plays vital anti-microbial roles in innate immunity
(
Granger, Perfect, & Durack, 1986; Green, Meltzer, Hibbs, & Nacy, 1990;
Iyengar, Stuehr, & Marletta, 1987; Liew, Millott, Parkinson, Palmer, &
Moncada, 1990; Marletta, Yoon, Iyengar, Leaf, & Wishnok, 1988; Stuehr,
Gross, Sakuma, Levi, &Nathan, 1989
) and that microorganisms have evolved
a large number of NO-sensitive targets and defence mechanisms against its
toxic effects.
FHbs catalyse reaction of NO with O
2
to yield the relatively innocuous
NO
3
(
Gardner, 2005; Mowat, Gazur, Campbell, & Chapman, 2010;
Poole & Hughes, 2000
) by a dioxygenase (
Gardner et al., 2006, 2000;
Gardner, Gardner, Martin, & Salzman, 1998
) or denitrosylase (
Hausladen,
Gow, & Stamler, 1998, 2001
). Anaerobically, Hmp shows low
NO-reductase activity, converting NO to N
2
O
Kim, Orii, Lloyd,
Hughes, & Poole, 1999; Liu, Zeng, Hausladen, Heitman, & Stamler,
2000; Poole & Hughes, 2000; Vinogradov & Moens, 2008
).
Deletion of the
hmp
gene alone abolishes the NO-consuming activity
(
Liu et al., 2000
) and is sufficient to render bacteria hypersensitive to NO
and related compounds, not only
in vitro
(
Membrillo-Hern´ndez et al.,
1999
) but also
in vivo
(
Stevanin, Poole, Demoncheaux, & Read, 2002
).
Similar to
E. coli
(
Stevanin, Read, & Poole, 2007
), the
S. enterica
serovar
Typhimurium mutant defective in FHb shows enhanced sensitivity to
mouse and human-macrophage microbicidal activity (
Gilberthorpe et al.,
2007; Stevanin et al., 2002
), suggesting that the globin contributes to pro-
tection from NO-mediated toxicity in macrophages.
FHbs from several other bacteria show protective functions against
RNS, such as those from
Ralstonia eutropha
,
Bacillus subtilis
,
Pseudomonas
aeruginosa
,
Deinococcus radiodurans
,
S. enterica
and
Klebsiella pneumoniae
(reviewed by
Frey, Farres, Bollinger, & Kallio, 2002
).
Although FHbs protect pathogenic microorganisms from the host
immune systems,
they also defend non-pathogenic organisms
from
