Biology Reference
In-Depth Information
Abstract
Evolution allowed Antarctic microorganisms to grow successfully under extreme
conditions (low temperature and high O
2
content), through a variety of structural
and physiological adjustments in their genomes and development of programmed
responses to strong oxidative and nitrosative stress. The availability of genomic
sequences from an increasing number of cold-adapted species is providing insights
to understand the molecular mechanisms underlying crucial physiological processes
in polar organisms. The genome of Pseudoalteromonas haloplanktis TAC125 contains
multiple genes encoding three distinct truncated globins exhibiting the 2/2 a-helical
fold. One of these globins has been extensively characterised by spectroscopic
analysis, kinetic measurements and computer simulation. The results indicate unique
adaptive structural properties that enhance the overall flexibility of the protein, so that
the structure appears to be resistant to pressure-induced stress. Recent results on a
genomic mutant strain highlight the involvement of the cold-adapted globin in
the protection against the stress induced by high O
2
concentration. Moreover, the
protein was shown to catalyse peroxynitrite isomerisation in vitro. In this review,
we first summarise how cold temperatures affect the physiology of microorganisms
and focus on the molecular mechanisms of cold adaptation revealed by recent
biochemical and genetic studies. Next, since only in a very few cases the physiological
role of truncated globins has been demonstrated, we also discuss the structural
and functional features of the cold-adapted globin in an attempt to put into perspective
what has been learnt about these proteins and their potential role in the biology of
cold-adapted microorganisms.
ABBREVIATIONS
CAP
cold-adapted protein
CSP
cold-shock protein
Cygb
cytoglobin
FHb
flavohaemoglobin
Hb
haemoglobin
Hmp
FHb from
E. coli
HSP
heat-shock protein
Mb
myoglobin
Ngb
neuroglobin
PhTAC125 Pseudoalteromonas haloplanktis
TAC125
PTS
phosphoenolpyruvate-dependent phosphotransferase system
RNS
reactive nitrogen species
ROS
reactive oxygen species
SDgb
single-domain globin
TBDTs
TonB-dependent transport systems
TF
trigger factor
