HEXAMERIC STRUCTURE OF COLD ACTIVE BETA-GALACTOSIDASE FROM ARTHROBACTER SP. C2-2

T. Skálová¹, J. Dohnálek¹, E. Vondráčková¹, H. Petroková¹, P. Lipovová², V. Spiwok², H. Strnad², B. Králová² and J. Hašek¹

¹ Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, 162 06 Praha 6, Czech Republic

² Institute of Chemical Technology, Technická 5, 166 28 Praha 6, Czech Republic

Arthrobacter sp. C2-2, a soil bacteria found in Antarctica, belongs to psychrotrophic, i.e. cold tolerant, microorganisms. Two beta-galactosidases, isoenzymes C-2-2-1 and C-2-2-2, were isolated from this bacterium. In this contribution, we would like to present an X-ray structure of C-2-2-1 beta-galactosidase from Arthrobacter sp. C2-2, which was solved at 1.9 Å resolution.

The beta-galactosidase belongs to glycosyl hydrolase structural family 2. It is composed of 1023 amino acid residues and can be divided into five structural domains. The active site of the beta-galactosidase is localized within the TIM barrel domain. The beta-galactosidase cleaves beta-galactosides by separating of its terminal galactose group and it also catalyzes transglycosylation. Typically, it cleaves lactose into galactose and glucose.

The fold of this beta-galactosidase is similar to that of Escherichia coli, which belongs to the same glycosyl hydrolase family 2 and structure of which was studied in details. It is known that Escherichia coli beta-galactosidase forms tetramers and that its tetrameric state is necessary for activity.

On the contrary to this, we found that C-2-2-1 beta-galactosidase from Arthrobacter sp. C2-2 forms compact hexamers in crystal structure.

Acknowledgement: The research was supported by the Grant Agency of the Czech Republic (project 204/02/0843/A) and by the Academy of Sciences of the Czech Republic (projects AVOZ40500505 and B500 500 512).