1g6a
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PSE-4 CARBENICILLINASE, R234K MUTANT
OverviewOverview
PSE-4 is a class A beta-lactamase produced by strains of Pseudomonas, aeruginosa and is highly active for the penicillin derivative, carbenicillin. The crystal structure of the wild-type PSE-4, carbenicillinase has been determined to 1.95 A resolution by molecular, replacement and represents the first structure of a carbenicillinase, published to date. A superposition of the PSE-4 structure with that of, TEM-1 shows a rms deviation of 1.3 A for 263 Calpha atoms. Most, carbenicillinases are unique among class A beta-lactamases in that residue, 234 is an arginine (ABL standard numbering scheme), while in all other, class A enzymes this residue is a lysine. Kinetic characterization of a, R234K PSE-4 mutant reveals a 50-fold reduction in k(cat)/K(m) and confirms, the importance of Arg 234 for carbenicillinase activity. A comparison of, the structure of the R234K mutant refined to 1.75 A resolution with the, wild-type structure shows that Arg 234 stabilizes an alternate, conformation of the Ser 130 side chain, not seen in other class A, beta-lactamase structures. Our molecular modeling studies suggest that the, position of a bound carbenicillin would be shifted relative to that of a, bound benzylpenicillin in order to avoid a steric clash between the, carbenicillin alpha-carboxylate group and the conserved side chain of Asn, 170. The alternate conformation of the catalytic Ser 130 in wild-type, PSE-4 may be involved in accommodating this shift in the bound substrate, position.
About this StructureAbout this Structure
1G6A is a Single protein structure of sequence from Pseudomonas aeruginosa with SO4 as ligand. Active as Beta-lactamase, with EC number 3.5.2.6 Full crystallographic information is available from OCA.
ReferenceReference
Insights into the molecular basis for the carbenicillinase activity of PSE-4 beta-lactamase from crystallographic and kinetic studies., Lim D, Sanschagrin F, Passmore L, De Castro L, Levesque RC, Strynadka NC, Biochemistry. 2001 Jan 16;40(2):395-402. PMID:11148033
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