Event Title

Crystal Structure and kinetic Characterization of the Class D Carbapenemase OXA-23

Location

Hager-Lubbers Exhibition Hall

Start Date

16-4-2013 3:30 PM

Description

PURPOSE: OXA-23 is a class D β-lactamase found in clinically problematic strains of bacteria such as Acinetobacter baumannii. These enzymes hydrolyze β-lactam antibiotics, conferring resistance upon them. OXA-23 was the first class D enzyme reported with activity against carbapenem antibiotics and was thus used to define a new class of β-lactamases, the carbapenem hydrolyzing class D β-lactamases (CHDL). OXA-24, a better-studied CHDL, shares > 60% amino acid identity with OXA-23. In this study, we compared the efficacy of OXA-24 and OXA-23 against a variety of β-lactam substrates. These enzymes share similar kinetic profiles, but OXA-23 appears to have greater affinity for advanced generation cephalosporins than OXA-24. To help explore these differences, we examined OXA-23 via X-ray crystallography and here report the first structures of wild type OXA-23 as an apo enzyme and bound to a β-lactam substrate (doripenem). RESULTS: As predicted, OXA-23 shares a very similar active site topology with OXA-24 and includes the same residues thought to be responsible for β-lactam hydrolysis. Similar to OXA-24, OXA-23 has an active site bridge comprised of residues F110 and M221 that are responsible for the enzyme’s extraordinarily tight carbapenem affinity (< 50 nM). CONCLUSION: A comparison of the OXA-23 and OXA-24 structures reveals a shift in the loop between the b5-b6 sheets that is likely responsible for the increased affinity for cephalosporin substrates in OXA-23.

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Apr 16th, 3:30 PM

Crystal Structure and kinetic Characterization of the Class D Carbapenemase OXA-23

Hager-Lubbers Exhibition Hall

PURPOSE: OXA-23 is a class D β-lactamase found in clinically problematic strains of bacteria such as Acinetobacter baumannii. These enzymes hydrolyze β-lactam antibiotics, conferring resistance upon them. OXA-23 was the first class D enzyme reported with activity against carbapenem antibiotics and was thus used to define a new class of β-lactamases, the carbapenem hydrolyzing class D β-lactamases (CHDL). OXA-24, a better-studied CHDL, shares > 60% amino acid identity with OXA-23. In this study, we compared the efficacy of OXA-24 and OXA-23 against a variety of β-lactam substrates. These enzymes share similar kinetic profiles, but OXA-23 appears to have greater affinity for advanced generation cephalosporins than OXA-24. To help explore these differences, we examined OXA-23 via X-ray crystallography and here report the first structures of wild type OXA-23 as an apo enzyme and bound to a β-lactam substrate (doripenem). RESULTS: As predicted, OXA-23 shares a very similar active site topology with OXA-24 and includes the same residues thought to be responsible for β-lactam hydrolysis. Similar to OXA-24, OXA-23 has an active site bridge comprised of residues F110 and M221 that are responsible for the enzyme’s extraordinarily tight carbapenem affinity (< 50 nM). CONCLUSION: A comparison of the OXA-23 and OXA-24 structures reveals a shift in the loop between the b5-b6 sheets that is likely responsible for the increased affinity for cephalosporin substrates in OXA-23.