title: Identification of two aspartates and a glutamate essential for the activity of endo-beta-N-acetylglucosaminidase H from Streptomyces plicatus.
abstract: In order to identify groups essential for the activity of endo-beta-N-acetylglucosaminidase H (Endo H), all 8 glutamate residues, all 19 aspartates, and both tryptophans were individually substituted with glutamines, asparagines, and phenylalanines, respectively, by oligonucleotide site-directed mutagenesis. Only variants D170N, D172N, and E174Q were found to have specific activities significantly less than wild-type Endo H. Another variant, D173N, did not produce detectable amounts of protein. Wild-type enzyme was found to have a bell-shaped pH activity profile, which was retained in the essential aspartate mutants, but E174Q lost the basic pH limb of the curve, indicating that E174 is good candidate for the proton donating group necessary for catalysis. The general base needed for activity could not be unambiguously identified; although, of the essential aspartates, D172 is the only one conserved in other related glucosidases.
authors.affiliation: Genencor International, Inc., South San Francisco, California 94080.
authors.forename: B F
authors.initials: BF
authors.lastname: Schmidt
authors.forename: E
authors.initials: E
authors.lastname: Ashizawa
authors.forename: A S
authors.initials: AS
authors.lastname: Jarnagin
authors.forename: S
authors.initials: S
authors.lastname: Lynn
authors.forename: G
authors.initials: G
authors.lastname: Noto
authors.forename: L
authors.initials: L
authors.lastname: Woodhouse
authors.forename: D A
authors.initials: DA
authors.lastname: Estell
authors.forename: P
authors.initials: P
authors.lastname: Lad
mesh_terms: D000595:Amino Acid Sequence; D001224:Aspartic Acid; D001483:Base Sequence; D001665:Binding Sites; D004269:DNA, Bacterial / Q000378:metabolism; D005971:Glutamates; D018698:Glutamic Acid; D006596:Hexosaminidases / Q000096:biosynthesis / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D010957:Plasmids; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D015183:Restriction Mapping; D013302:Streptomyces / Q000201:enzymology*
chemical_list: D004269:DNA, Bacterial; D005971:Glutamates; D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D001224:Aspartic Acid; D018698:Glutamic Acid; D006596:Hexosaminidases; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase