W0020

The First Structure of a Family 53 Glycosyl Hydrolase. Ryttersgaard C. and Larsen S., Centre for Crystallographic Studies, University of Copenhagen, 5 Universitetsparken, Copenhagen DK 2100, Denmark

The beta-1,4-Galactanase from Aspergillus aculeatus has been isolated and expressed in Aspergillus oryzae[1]. It is composed of a single polypeptide chain of 334 amino acids, which has a large excess of negatively charged amino acid residues compared to the number of positively charged residues. The isoelectric point (pI) has been measured to 2.85, which explains why calcium ions are necessary in the crystallization. The SHARP program[2] has been used to solve the structure with Multiple Isomorphous Replacement.

Beta-1,4-Galactanase belongs to family 53 of the glycosyl hydrolases[3] and represents the first three dimensional structure from this family. The enzyme is an endo-glycosyl hydrolase which degrades trimers of galactan in a retaining mechanism. Galactan is one of the side chains in pectin, which is a major component of plant cell walls.

The structure will be presented along with a discussion of the catalytic machinery and substrate specificity.

[1] S. Christgau, T. Sandal, L. V. Kofod, and H. Dalbøge, Current genetics, 27: 135-141, 1995

[2] E. de La Fortelle and G. Bricogne (1997).

[3] B. Henrissat and A. Bairoch, Biochem. J., 316: 695-696, 1996