Characterization of the active site of group B streptococcal hyaluronan lyase

Hyaluronan lyase is secreted by most strains of the human pathogen, group B streptococcus. Site-directed mutagenesis of the enzyme identified three am ino acid residues important for enzyme activity, H479, Y488, and R542, Thes e three residues are in close proximity in the putative active site of a ho mology model of group B streptococcal hyaluronan lyase, The homology model was based on the crystal structure of another related glycosaminoglycan lya se, chondroitin AC lyase, which exhibits different substrate specificity. T wo asparagine residues in the active site groove, N429 and N660, were also found to be essential for enzyme activity. In addition, conversion of two a djacent tryptophan residues in the groove to alanines abolished activity. A ll amino acids found to be essential in GBS hyaluronan lyase are conserved in both enzymes. However, several amino acids in the active site groove of the two enzymes are not conserved, In the 18 cases in which one of these am ino acids in GBS hyaluronan lyase was replaced with its corresponding amino acid in chondroitin AC lyase, no major loss of activity or change in subst rate specificity was observed. (C) 2000 Wiley-Liss, Inc.