A Pseudo-Michaelis Quaternary Complex in the Reverse Reaction of a Ligase: Structure of Escherichia coli B Glutathione Synthetase Complexed with ADP, Glutathione, and Sulfate at 2.0 Å Res
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- 作者：Takane Hara ; Hiroaki Kato ; Yukiteru Katsube ; and Jun'ichi Oda
- 刊名：Biochemistry
- 出版年：1996
- 出版时间：September 17, 1996
- 年：1996
- 卷：35
- 期：37
- 页码：11967 - 11974
- 全文大小：531K
- 年卷期：v.35,no.37(September 17, 1996)
- ISSN：1520-4995
文摘
The crystal structure of glutathione synthetase fromEscherichia coli B complexed withADP,glutathione, and sulfate has been determined at 2.0 Å resolution.Concerning the chemical similarity ofsulfate and phosphate, this quaternary complex structure represents apseudo enzyme-substrate complexin the reverse reaction and consequently allows us to understand theactive site architecture of the E. coliglutathione synthetase. Two Mg2+ ions arecoordinated with oxygen atoms from the 
- and
-phosphategroups of ADP and from the sulfate ion. The flexible loops,invisible in the unliganded or the binary andternary complex structures, are fixed in the quaternary complex.The larger flexible loop (Ile226-Arg241)includes one turn of a 310-helix that comprises the bindingsite of the glycine moiety of GSH. The smallloop (Gly164-Gly167) is involved in nucleotide binding and acts as aphosphate gripper. The side chainsof Arg210 and Arg225 interact with the sulfate ion and the-phosphate moiety of ADP. Arg 210 islikely to interact with the carboxylate of the C-terminal
-glutamylcysteine in the substrate-binding formof the forward reaction. Other positively charged residues in theactive site (Lys125 and Lys160) areinvolved in nucleotide binding, directing the phosphate groups to theright position for catalysis. Functionalaspects of the active site architecture in the substrate-binding formare discussed.
- and-phosphategroups of ADP and from the sulfate ion. The flexible loops,invisible in the unliganded or the binary andternary complex structures, are fixed in the quaternary complex.The larger flexible loop (Ile226-Arg241)includes one turn of a 310-helix that comprises the bindingsite of the glycine moiety of GSH. The smallloop (Gly164-Gly167) is involved in nucleotide binding and acts as aphosphate gripper. The side chainsof Arg210 and Arg225 interact with the sulfate ion and the-phosphate moiety of ADP. Arg 210 islikely to interact with the carboxylate of the C-terminal-glutamylcysteine in the substrate-binding formof the forward reaction. Other positively charged residues in theactive site (Lys125 and Lys160) areinvolved in nucleotide binding, directing the phosphate groups to theright position for catalysis. Functionalaspects of the active site architecture in the substrate-binding formare discussed.