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J. Biol. Chem., Vol. 265, Issue 12, 6827-6835, Apr, 1990
Analyses of catalytic activity and inhibitor binding of human acid beta- glucosidase by site-directed mutagenesis. Identification of residues critical to catalysis and evidence for causality of two Ashkenazi Jewish Gaucher disease type 1 mutations
ME Grace, PN Graves, FI Smith and GA Grabowski
Division of Medical and Molecular Genetics, Mount Sinai School of Medicine, New York, New York 10029.
Analyses of catalytic properties and inhibitor binding were conducted to
investigate the molecular basis of active site function of human acid
beta-glucosidases (EC 3.2.1.45) expressed from normal and Gaucher disease
Type 1 alleles. Comparative studies were conducted with enzymes expressed
from natural (spleen and fibroblasts) alleles or from mutagenized cDNAs in
Spodoptera frugiperda (Sf9) cells using the baculovirus expression system.
Mutant cDNAs containing Thr43 to Lys43 (beta-GlcThr43----Lys) and Asp358 to
Glu358 (beta-GlcAsp358----Glu) substitutions and two cDNAs containing
Ashkenazi Jewish Gaucher disease Type 1 mutations, Arg120 to Gln120
(beta-GlcArg120----Gln) and Asn370 to Ser370 (beta-GlcAsn370----Ser) were
expressed and the gene products characterized by enzymatic, immunologic,
and inhibitor studies. Genotypes at the acid beta-glucosidase locus in
selected Gaucher disease Type 1 patients were determined by allele-specific
oligonucleotide hybridization of amplified genomic DNA. Compared with
normal, recombinant or natural enzymes expressed from beta-GlcAsn370----
Ser alleles had about 2-5-fold decreased specific activity based on CRIM
(cross-reacting immunologic material). The beta-GlcArg120----Gln cDNA
expressed catalytically inactive CRIM in Sf9; consistent with the 9-fold
decreased CRIM-specific activity of the natural enzyme from a
beta-GlcArg120----Gln/beta-GlcAsn370----Ser genetic compound. The beta-
GlcAsp358----Glu cDNA expressed catalytically inactive CRIM in Sf9 cells.
The presence of natural or recombinant enzyme expressed from
beta-GlcAsn370----Ser alleles was sufficient to confer 3-5-fold increased
IC50 values for deoxynojirimycin, glucosylsphingosine, and N-
alkyl-glucosylamine derivatives. Progress curves for inhibition by the
slow-tight binding N-alkyl-glucosylamines indicated that the beta-Glc-
Asn370----Ser mutation did not alter a conformational change induced by
these reaction intermediate analogues. These results provide evidence that
the beta-GlcArg120----Gln and beta-GlcAsn370----Ser mutations found in
Gaucher disease Type 1 patient genomes are the molecular bases of the
enzymatic dysfunction. In addition, the region including Arg120 and that
encompassing Asp358 and Asn370 contain residues critical to active site
formation or participation in the catalytic mechanism.

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Copyright © 1990 by the American Society for Biochemistry and Molecular Biology.
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