Human lysosomal beta-hexosaminidases are dimeric enzymes composed of alpha and beta-chains, encoded by the genes HEXA and HEXB. They occur in three isoforms, the homodimeric hexosaminidases B (betabeta) and S (alphaalpha), and the heterodimeric hexosaminidase A (alphabeta), where dimerization is required for catalytic activity ...
Human lysosomal beta-hexosaminidases are dimeric enzymes composed of alpha and beta-chains, encoded by the genes HEXA and HEXB. They occur in three isoforms, the homodimeric hexosaminidases B (betabeta) and S (alphaalpha), and the heterodimeric hexosaminidase A (alphabeta), where dimerization is required for catalytic activity. Allelic variations in the HEXA and HEXB genes cause the fatal inborn errors of metabolism Tay-Sachs disease and Sandhoff disease, respectively. Here, we present the crystal structure of a complex of human beta-hexosaminidase B with a transition state analogue inhibitor at 2.3A resolution (pdb 1o7a). On the basis of this structure and previous studies on related enzymes, a retaining double-displacement mechanism for glycosyl hydrolysis by beta-hexosaminidase B is proposed. In the dimer structure, which is derived from an analysis of crystal packing, most of the mutations causing late-onset Sandhoff disease reside near the dimer interface and are proposed to interfere with correct dimer formation. The structure reported here is a valid template also for the dimeric structures of beta-hexosaminidase A and S.
Related Citations:
Complete Analysis of the Glycosylation and Disulfide Bond Pattern of Human Beta-Hexosaminidase B by Maldi-Ms Schuette, C.G., Weissgerber, J., Sandhoff, K. (2001) Glycobiology 11: 549
Synthesis of a Human Lysosomal Enzyme, Beta-Hexosaminidase B, Using the Baculaovirus Expression System Boose, J.A., Tifft, C.J., Proia, R.L., Myerowitz, R. (1990) Protein Expr Purif 1: 111
Organizational Affiliation:
Institut für Chemie Kristallographie, Freie Universität Berlin, Takustrasse 6, 14195 Berlin, Germany.
AA [auth C] EA [auth E] FA [auth E] GA [auth E] KA [auth F]
AA [auth C], EA [auth E], FA [auth E], GA [auth E], KA [auth F], LA [auth F], MA [auth F], O [auth A], P [auth A], Q [auth A], T [auth B], U [auth B], V [auth B], Y [auth C], Z [auth C]
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