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PDBsum entry 1cg0
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Mechanistic implications from crystalline complexes of wild-Type and mutant adenylosuccinate synthetases from escherichia coli.
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Authors
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J.Y.Choe,
B.W.Poland,
H.J.Fromm,
R.B.Honzatko.
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Ref.
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Biochemistry, 1999,
38,
6953-6961.
[DOI no: ]
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PubMed id
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Abstract
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Asp13 and His41 are essential residues of adenylosuccinate synthetase,
putatively catalyzing the formation of adenylosuccinate from an intermediate of
6-phosphoryl-IMP. Wild-type adenylosuccinate synthetase and three mutant
synthetases (Arg143 --> Leu, Lys16 --> Gln, and Arg303 --> Leu) from
Eschericha coli have been crystallized in the presence of IMP, hadacidin (an
analogue of L-aspartate), Mg2+, and GTP. The active site of each complex
contains 6-phosphoryl-IMP, Mg2+, GDP, and hadacidin, except for the Arg303
--> Leu mutant, which does not bind hadacidin. In response to the formation
of 6-phosphoryl-IMP, Asp13 enters the inner coordination sphere of the active
site Mg2+. His41 hydrogen bonds with 6-phosphoryl-IMP, except in the Arg303
--> Leu complex, where it remains bound to the guanine nucleotide. Hence,
recognition of the active site Mg2+ by Asp13 evidently occurs after the
formation of 6-phosphoryl-IMP, but recognition of the intermediate by His41 may
require the association of L-aspartate with the active site. Structures reported
here support a mechanism in which Asp13 and His41 act as the catalytic base and
acid, respectively, in the formation of 6-phosphoryl-IMP, and then act together
as catalytic acids in the subsequent formation of adenylosuccinate.
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