Identification of a catalytic residue of Clostridium paraputrificum N-acetyl-beta-D-glucosaminidase Nag3A by site-directed mutagenesis.
Clostridium paraputrificum M-21 beta-N-acetylglucosaminidase 3A (Nag3A) is an enzyme classified in family 3 of the glycoside hydrolases. To identify catalytic residues of this enzyme, mutations were introduced into highly conserved Glu and Asp residues. Replacement of Asp175 with Ala abolished the catalytic activity without change in the circular dichroism spectrum, strongly suggesting that this residue is a catalytic residue, a nucleophile/base or a proton donor. Since the K(m) values of mutant enzymes D119N, D229N, D229A and D274N increased 17 to 41 times as compared with that of wild-type enzyme, Asp119, Asp229, and Asp274 appear to be involved in substrate recognition and binding. Taking previous studies into consideration, we presume that Asp303 is the catalytic nucleophile and Asp175 is the proton donor of C. paraputrificum Nag3A.
Li
Huazhong
H
School of Medicine, Southern Yangtze University, Wuxi, China.
Zhao
Guangshan
G
Miyake
Hideo
H
Umekawa
Hayato
H
Kimura
Tetsuya
T
Ohmiya
Kunio
K
Sakka
Kazuo
K
D000118:Acetylglucosaminidase / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001224:Aspartic Acid / Q000737:chemistry* / Q000235:genetics; D002384:Catalysis; D020134:Catalytic Domain / Q000235:genetics*; D002942:Circular Dichroism; D003013:Clostridium / Q000201:enzymology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D013379:Substrate Specificity
D001224:Aspartic Acid; D000118:Acetylglucosaminidase