Structures of the psychrophilic Alteromonas haloplanctis α-amylase give insights into cold adaptation at a molecular level

Background: Enzymes from psychrophilic (cold-adapted) microorganisms operate at temperatures close to 0 degrees C, where the activity of their mesophilic and thermophilic counterparts is drastically reduced. It has generally been assumed that thermophily is associated with rigid proteins, whereas psychrophilic enzymes have a tendency to be more flexible. Results: Insights into the cold adaptation of proteins are gained on the basis of a psychrophilic protein's molecular structure. To this' end, we have determined the structure of the recombinant form of a psychrophilic a-amylase from Alteromonas haloplanctis at 2.4 Angstrom resolution. We have compared this with the structure of the wild-type enzyme, recently solved at 2.0 Angstrom resolution, and with available structures of their mesophilic counterparts. These comparative studies have enabled us to identify possible determinants of cold adaptation. Conclusions: We propose that an increased resilience of the molecular surface and a less rigid protein core, with less interdomain interactions, are determining factors of the conformational flexibility that allows efficient enzyme catalysis in cold environments.