The 1.8 A structures of leech intramolecular trans-sialidase complexes: evidence of its enzymatic mechanism.
Intramolecular trans-sialidase from leech (Macrobdella decora) is the first member of the sialidase superfamily found to exhibit strict specificity towards the cleavage of terminal Neu5Acalpha2-->3Gal linkage in sialoglycoconjugates. Its release of 2,7-anhydro-Neu5Ac instead of Neu5Ac indicates that it catalyzes an intramolecular trans-sialosyl reaction. Crystal structures of its complexes with an inactive substrate analogue 2-propenyl-Neu5Ac, and with the product 2,7-anhydro-Neu5Ac, have been determined to 1.8 A resolution. The boat conformation of the pyranose observed in the complexes supports the proposed enzymatic mechanism that O7 of an axial 6-glycerol group attacks the positively charged C2 of the intermediate. A generalized mechanism is proposed for the sialidase superfamily.
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Center for Macromolecular Crystallography, University of Alabama at Birmingham, AL, 35294, USA.
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D000595:Amino Acid Sequence; D000818:Animals; D001224:Aspartic Acid; D002384:Catalysis; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007865:Leeches / Q000201:enzymology; D008969:Molecular Sequence Data; D019158:N-Acetylneuraminic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D009439:Neuraminidase / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D014443:Tyrosine
D001224:Aspartic Acid; D014443:Tyrosine; D009439:Neuraminidase; D019158:N-Acetylneuraminic Acid