Abstract: Naturally occurring peptidases from organisms living under extreme
conditions are adapted to function in environmental extremes, including
temperature, salinity, pH, or pressure. These organisms represent unique
sources for new bio-molecules that have both industrial and medicinal
application. Adaptive strategies for functioning under extreme conditions are
reflected at the enzyme sequence and structural level. Understanding the
determinants responsible for unique functional features can be used to enhance
the functional features of known proteins. In the present study, the amino acid
sequences of 81 peptidases of the thermolysin (M4) family were analyzed for
possible determinants of psychrophilic and thermophilic features, by comparing
with thermolysin from Bacillus thermoproteolyticus, the prototype enzyme
of the family. The analysis indicated that M4 peptidases from cold-adapted
species have fewer arginines and more lysines, and also fewer tyrosines and
more phenylalanines than the prototype thermolysin. However, the opposite was
true for M4 peptidases from thermophilic species. For sequences from
thermophilic species the ratio of the seven amino acids I,V,Y,W,R,E,L were
correlated to optimal growth temperature.
