1cg3
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STRUCTURE OF THE MUTANT (R143L) OF ADENYLOSUCCINATE SYNTHETASE FROM E. COLI COMPLEXED WITH HADACIDIN, GDP, 6-PHOSPHORYL-IMP, AND MG2+
OverviewOverview
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.
About this StructureAbout this Structure
1CG3 is a Single protein structure of sequence from Escherichia coli with MG, HDA, IMO and GDP as ligands. Active as Adenylosuccinate synthase, with EC number 6.3.4.4 Full crystallographic information is available from OCA.
ReferenceReference
Mechanistic implications from crystalline complexes of wild-type and mutant adenylosuccinate synthetases from Escherichia coli., Choe JY, Poland BW, Fromm HJ, Honzatko RB, Biochemistry. 1999 May 25;38(21):6953-61. PMID:10346917
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