1G6A

PSE-4 CARBENICILLINASE, R234K MUTANT

Summary for 1G6A

• Entry DOI: 10.2210/pdb1g6a/pdb
• Related: 1G68
• Descriptor: BETA-LACTAMASE PSE-4, SULFATE ION (3 entities in total)
• Functional Keywords: class a beta-lactamase, carbenicillinase, r234k mutant, hydrolase
• Biological source: Pseudomonas aeruginosa
• Total number of polymer chains: 1
• Total formula weight: 29624.22

Authors

Lim, D.,Sanschagrin, F.,Passmore, L.,De Castro, L.,Levesque, R.C.,Strynadka, N.C.J. (deposition date: 2000-11-03, release date: 2001-02-21, Last modification date: 2024-10-30)

Primary citation

Lim, D.,Sanschagrin, F.,Passmore, L.,De Castro, L.,Levesque, R.C.,Strynadka, N.C.
Insights into the molecular basis for the carbenicillinase activity of PSE-4 beta-lactamase from crystallographic and kinetic studies.
Biochemistry, 40:395-402, 2001

PubMed Abstract: 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.

PubMed: 11148033
DOI: 10.1021/bi001653v

Experimental method

X-RAY DIFFRACTION (1.75 Å)