Title

Structural and Kinetic Studies on Metallo-β-lactamase IMP-1

Document Type

Article

Language

eng

Format of Original

10 p.

Publication Date

10-22-2011

Publisher

American Chemical Society

Source Publication

Biochemistry

Source ISSN

0006-2960

Original Item ID

doi: 10.1021/bi200839h

Abstract

In an effort to probe for metal binding to metallo-β-lactamase (MβL) IMP-1, the enzyme was overexpressed, purified, and characterized. The resulting enzyme was shown to bind 2 equiv of Zn(II), exhibit significant catalytic activity, and yield EXAFS results similar to crystallographic data previously reported. Rapid kinetic studies showed that IMP-1 does not stabilize a nitrocefin-derived reaction intermediate; rather, the enzyme follows a simple Michaelis mechanism to hydrolyze nitrocefin. Metal-substituted and metal-reconstituted analogues of IMP-1 were prepared by directly adding metal ion stocks to metal-free enzyme, which was generated by dialysis versus EDTA. UV–vis studies on IMP-1 containing 1 equiv of Co(II) showed a strong ligand-to-metal charge transition at 340 nm, and the intensity of this feature increased when the second equivalent of Co(II) was added to the enzyme. EXAFS fits on IMP-1 containing 1 equiv of Co(II) strongly suggest the presence of a metal–metal interaction, and EPR spectra of the IMP-1 containing 1 and 2 equiv of Co(II) are very similar. Taken together, steady-state kinetic and spectroscopic studies suggest that metal binding to metal-free IMP-1 follows a positive-cooperative mode.

Comments

Biochemistry, Vol. 50, No. 42 (October 22, 2011): 9125-9134. DOI.

Brian Bennett was affiliated with the Medical College of Wisconsin at the time of publication.