Reexamination of the role of Asp20 in catalysis by bacteriophage T4 lysozyme.
Replacement of Asp20 in T4 lysozyme by Cys produces a variant with (1) nearly wild-type specific activity, (2) a newly acquired sensitivity to thiol-modifying reagents, and (3) a pH-activity profile that is very similar to that of the wild-type enzyme. These results indicate that the residue at position 20 has a significant nucleophilic function rather than merely an electrostatic role. The intermediate in catalysis by lysozyme is probably a covalent glycosyl-enzyme instead of the ion pair originally proposed.
Hardy
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LW
Department of Molecular Genetics and Microbiology, University of Massachusetts, Worcester 01655.
Poteete
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AR
D001224:Aspartic Acid / Q000737:chemistry; D001483:Base Sequence; D001665:Binding Sites; D002384:Catalysis; D003545:Cysteine / Q000737:chemistry; D004252:DNA Mutational Analysis; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D009113:Muramidase / Q000378:metabolism*; D011994:Recombinant Proteins; D012483:Salmonella Phages / Q000201:enzymology / Q000235:genetics; D013329:Structure-Activity Relationship; D013604:T-Phages / Q000201:enzymology*
D011994:Recombinant Proteins; D001224:Aspartic Acid; D009113:Muramidase; D003545:Cysteine