Crystal structures of g-type lysozyme from Atlantic cod shed new light on substrate binding and the catalytic mechanism.
Crystal structures of Atlantic cod lysozyme have been solved with and without ligand bound in the active site to 1.7 and 1.9 A resolution, respectively. The structures reveal the presence of NAG in the substrate binding sites at both sides of the catalytic Glu73, hence allowing the first crystallographic description of the goose-type (g-type) lysozyme E-G binding sites. In addition, two aspartic acid residues suggested to participate in catalysis (Asp101 and Asp90) were mutated to alanine. Muramidase activity data for two single mutants and one double mutant demonstrates that both residues are involved in catalysis, but Asp101 is the more critical of the two. The structures and activity data suggest that a water molecule is the nucleophile completing the catalytic reaction, and the roles of the aspartic acids are to ensure proper positioning of the catalytic water.
Helland
Ronny
R
Department of Chemistry, The Norwegian Structural Biology Centre, University of Tromsø, 9037 Tromsø, Norway. Ronny.Helland@uit.no
Larsen
Renate L
RL
Finstad
Solrun
S
Kyomuhendo
Peter
P
Larsen
Atle N
AN
D000595:Amino Acid Sequence; D000818:Animals; D001224:Aspartic Acid / Q000737:chemistry; D001665:Binding Sites; D002645:Chickens; D018360:Crystallography, X-Ray; D048389:Gadus morhua / Q000235:genetics / Q000378:metabolism*; D005777:Geese; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009113:Muramidase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D016415:Sequence Alignment
D001224:Aspartic Acid; D009113:Muramidase