1swv
From Proteopedia
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Crystal structure of the D12A mutant of phosphonoacetaldehyde hydrolase complexed with magnesium
Overview
The 2-haloalkanoic acid dehalogenase (HAD) family, which contains both, carbon and phosphoryl transferases, is one of the largest known enzyme, superfamilies. HAD members conserve an alpha,beta-core domain that frames, the four-loop active-site platform. Each loop contributes one or more, catalytic groups, which function in mediating the core chemistry (i.e., group transfer). In this paper, we provide evidence that the number of, carboxylate residues on loop 4 and their positions (stations) on the loop, are determinants, and therefore reliable sequence markers, for metal ion, activation among HAD family members. Using this predictor, we conclude, that the vast majority of the HAD members utilize a metal cofactor., Analysis of the minimum requirements for metal cofactor binding was, carried out using Mg(II)-activated Bacillus cereus phosphonoacetaldehyde, hydrolase (phosphonatase) as an experimental model for metal-activated HAD, members. Mg(II) binding occurs via ligation to the loop 1 Asp12, carboxylate and Thr14 backbone carbonyl and to the loop 4 Asp186, carboxylate. The loop 4 Asp190 forms a hydrogen bond to the Mg(II) water, ligand. X-ray structure determination of the D12A mutant in the presence, of the substrate phosphonoacetaldehyde showed that replacement of the loop, 1 Asp, common to all HAD family members, with Ala shifts the position of, Mg(II), thereby allowing innersphere coordination to Asp190 and causing a, shift in the position of the substrate. Kinetic analysis of the loop 4, mutants showed that Asp186 is essential to cofactor binding while Asp190, simply enhances it. Within the phosphonatase subfamily, Asp186 is, stringently conserved, while either position 185 or position 190 is used, to position the second loop 4 Asp residue. Retention of a high level of, catalytic activity in the G185D/D190G phosphonatase mutant demonstrated, the plasticity of the metal binding loop, reflected in the variety of, combinations in positioning of two or three Asp residues along the, seven-residue motif of the 2700 potential HAD sequences that were, examined.
About this Structure
1SWV is a Single protein structure of sequence from Bacillus cereus with MG as ligand. Active as Phosphonoacetaldehyde hydrolase, with EC number 3.11.1.1 Full crystallographic information is available from OCA.
Reference
Investigation of metal ion binding in phosphonoacetaldehyde hydrolase identifies sequence markers for metal-activated enzymes of the HAD enzyme superfamily., Zhang G, Morais MC, Dai J, Zhang W, Dunaway-Mariano D, Allen KN, Biochemistry. 2004 May 4;43(17):4990-7. PMID:15109258
Page seeded by OCA on Wed Nov 21 02:48:08 2007
