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

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