Toward a molecular understanding of cold activity of enzymes from psychrophiles

Despite the fact that a much greater proportion of the earth environment is cold rather than hot, much less is known about psychrophilic, cold-adapted microorganisms compared with thermophiles living at high temperatures. In particular, investigation of the molecular basis of cold-active enzymes from psychrophiles has only recently received concerted research attention, in measure as a result of the EC-funded project COLDZYME. This research effort has been stimulated by the realization that such coldactive enzymes offer novel opportunities for biotechnological exploitation. Only very recently has the first cold-active enzyme, alpha-amylase, been crystallized, and this success was followed rapidly by others. This effort has facilitated a direct approach to solving the three-dimensional structure of cold-active enzymes to complement the gene homology modeling that had been performed previously, Recently studies have highlighted how different adaptations are used by different enzymes to achieve conformational flexibility at low temperatures, and how such adaptations are not necessarily the opposite of those that confer thermostability to proteins in thermophilic counterparts. This review also highlights initial successes in engineering genetically improved thermal stability in cold-active enzymes to give improved catalysts for low-temperature biotechnology.