1b6r
From Proteopedia
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N5-CARBOXYAMINOIMIDAZOLE RIBONUCLEOTIDE SYNTHETASE FROM E. COLI
Overview
Escherichia coli PurK, a dimeric N5-carboxyaminoimidazole ribonucleotide, (N5-CAIR) synthetase, catalyzes the conversion of 5-aminoimidazole, ribonucleotide (AIR), ATP, and bicarbonate to N5-CAIR, ADP, and Pi., Crystallization of both a sulfate-liganded and the MgADP-liganded E. coli, PurK has resulted in structures at 2.1 and 2.5 A resolution, respectively., PurK belongs to the ATP grasp superfamily of C-N ligase enzymes. Each, subunit of PurK is composed of three domains (A, B, and C). The B domain, contains a flexible, glycine-rich loop (B loop, T123-G130) that is, disordered in the sulfate-PurK structure and becomes ordered in the, MgADP-PurK structure. MgADP is wedged between the B and C domains, as with, all members of the ATP grasp superfamily. Other enzymes in this, superfamily contain a conserved Omega loop proposed to interact with the B, loop, define the specificity of their nonnucleotide substrate, and protect, the acyl phosphate intermediate formed from this substrate. PurK contains, a minimal Omega loop without conserved residues. In the reaction catalyzed, by PurK, carboxyphosphate is the putative acyl phosphate intermediate. The, sulfate of the sulfate ion-liganded PurK interacts electrostatically with, Arg 242 and the backbone amide group of Asn 245, components of the J loop, of the C domain. This sulfate may reveal the location of the, carboxyphosphate binding site. Conserved residues within the C-terminus of, the C domain define a pocket that is proposed to bind AIR in collaboration, with an N-terminal strand loop helix motif in the A domain (P loop, G8-L1). The P loop is proposed to bind the phosphate of AIR on the basis, of similar binding sites observed in PurN and PurE and proposed in PurD, and PurT, four other enzymes in the purine pathway.
About this Structure
1B6R is a Single protein structure of sequence from Escherichia coli with SO4 as ligand. Active as Phosphoribosylaminoimidazole carboxylase, with EC number 4.1.1.21 Full crystallographic information is available from OCA.
Reference
Three-dimensional structure of N5-carboxyaminoimidazole ribonucleotide synthetase: a member of the ATP grasp protein superfamily., Thoden JB, Kappock TJ, Stubbe J, Holden HM, Biochemistry. 1999 Nov 23;38(47):15480-92. PMID:10569930
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