Molecular modelling of a psychrophilic β-galactosidase

Abstract

An Antarctic strain of bacteria was isolated from the digestive tract of the crustacean Thysanoessa macrura and classified as Pseudoalteromonas sp. 22b based on 16SrRNA gene sequence and physiological as well as biochemical properties. This bacterium turned out to be a good producer of a cold-adapted β-galactosidase. The enzyme displays high catalytic and molecular adaptation to low temperatures. Here we present a homology model of the psychrophilic β-galactosidase based on the structural template of the mesophilic β-galactosidase from Escherichia coli (PDB code: 1JZ7, resolution 1.5 Å). Our aim was to identify and characterize potential cold-adaptational features of the target psychrophilic β-galactosidase at the level of the three-dimensional structure rather than solely from the analysis of the amino acid sequence. We report the results of comparisons between the psychrophilic and mesophilic β-galactosidases and point out similarities and differences in the catalytic site and in other parts of the structure. The model allowed us to pinpoint a number of characteristics that are frequently observed in psychrophilic enzymes and allowed interpretation of the results of immunochemical and biochemical analyses.