Biology Reference
In-Depth Information
Antarctic organisms and the time scales in the context of geological and cli-
matic changes have been extensively analysed and discussed (
Peck, 2011
).
The structure and function of proteins are the basis for understanding the
evolutionary forces operating at sub-zero temperature, and—in this
context—the knowledge gained at the molecular level is also crucial for
predictions of the evolutionary consequences of global warming. In fact,
at all analysed levels, the functional adaptation to permanently low temper-
ature appears to require maintenance of flexibility of molecules in order to
adequately support the cellular functioning. Proteins are one main factor of
the ensuing mechanisms of adaptation.
Temperature is the prime driver that shaped the current structure and
function of polar communities. Amongst abiotic factors influenced by tem-
perature, O
2
and CO
2
, and their concentrations, play an important role in
life-sustaining processes. Due to low temperature, their concentrations are
several-fold higher than in temperate and tropical marine habitats. The
temperature-dependent balance between O
2
demand/supply and the
associated functional capacity for specific functions of macromolecules shape
the performance window in polar species (
P¨ rtner et al., 2007
). In polar
environments, the benefits of O
2
levels (high by default) are indeed largely
apparent, because they are counterbalanced by the kinetics of biological pro-
cesses operating at low temperature (
D'Amico et al., 2006
) which decreases
the rates, and by increased production of ROS. O
2
is obviously necessary for
aerobic bacterial metabolism, but it can become poisonous in triggering
oxidative-stress bursts.
In view of these considerations, in all Antarctic organisms, biological
processes envisaging O
2
(respiration, transport/release, scavenging, reactive
species, etc.) and other gases are bound to attract the interest of biologists.
In the realm of microbial life, the cold-adapted bacterial protein
Ph
-2/
2HbO displays hexacoordination of the ferric and ferrous haem-Fe atom
(
Giordano et al., 2011; Howes et al., 2011
). Investigating the features of this
globin, in an attempt to shed light on possible multiplicity of functions, has
been an important task. For instance,
Ph
-2/2HbO appears to exhibit a
pseudo-enzymatic function in which O
2
is involved (
Russo et al., 2013
)
and is available for reactions with NO to produce nitrate anions. In a single
molecule, multiple conformations (penta- vs. hexacoordinated states) may
account for multiple functions: under aerobic conditions, on one hand,
Ph
-2/2HbO provides cells with protection against NO and related RNS;
on the other, during the anaerobic phase,
Ph
-2/2HbO may provide
NO via nitrite reduction. The evidence summarised here indicates that
