A Comparison of Bacillus Cereus and Aeromonas Hydrophilia Zn-β-lactamases

Abstract

We have performed EXAFS studies on the B. cereus 5/B/6 and A. hydrophila enzymes, both at pH 6.5 containing about 1 equivalent of Zn. Note that the B. cereus enzymes from strains 5/B/6 and 568/H/9 differ in 17 aminoacid substitutions; none of which is located at the active site. Therefore, although the crystal structure of the 5/B/6 enzyme is not known similar metal coordination patterns are expected. For the A. hydrophila enzyme no crystal structure is available at present. Laboratory, Outstation Hamburg, Notkestr. 85, 22603 Hamburg, Germany, bFachdchtung 12.4 In an increasing number of pathogenic bacteria Zn-13-1actamases are being discovered as major factors of antibiotic resistance. For a possible strategy to fight these bacteria, it is important to understand the catalytic mechanism. X-ray absorption spectroscopy measurements on the zinc-K-edge of 13-1actamases from Bacillus cereus (strain 5/B/6) and Aeromonas hydrophila (AE 036) gives evidence for differences in the mode of zinc sulfur coordination and information about the coordination to N and O donor ligands. "European Molecular Biology

Metallo-?-lactamases: two binding sites for one catalytic metal ion?

“…It might be worth testing whether a translocation during the catalytic cycle of the enzymes could be part of the catalytic mechanism. This is also important since data obtained recently for the subclass B2 enzyme from A. hydrophila (CphA) suggest that the metal ion of the mononuclear enzyme is preferentially bound in the CysAsp-His site of the protein [51,52], which supports earlier findings demonstrating full occupation of the single metal ion with a Cys sulphur as a ligand [95,114]. But even for CphA it became apparent that the single metal ion in the Cd(II)-substituted enzyme shows two alternative ligand geometries [51].…”

“…Additionally, slightly differing ligand positions in occupied and unoccupied sites have been observed by comparison with a structure of the metal-free enzyme [43]. The distribution of zinc between the two sites in the Zn 1 enzyme, as has been demonstrated by EX-AFS spectroscopy of Zn 1 enzymes [14,54,95], might result in average electron densities, leading to incorrect positions of residues lying between the 'real' positions in occupied and unoccupied sites [54]. In contrast to X-ray crystallography, unoccupied sites do not contribute to the data in EXAFS spectroscopy.…”

Bacteria or melanosomes? A geochemical analysis of micro-bodies on a tadpole from the Oligocene Enspel Formation of Germany

“…The zinc in the human hair is also not a pure sample; there are likely to be contributions from both eu-and pheomelanin-bound zinc as well as that in proteins. The zinc XANES spectrum of the tadpole is also somewhat similar to that of zinc bound to bacterial enzymes (Meyer-Klaucke et al 1999;Outten et al 2001).…”

Kinetic and spectroscopic characterization of native and metal‐substituted β‐lactamase from Aeromonas hydrophila AE036

“…The EXAFS spectra of a freeze‐dried sample (top) and of a frozen solution (bottom) with theoretical fits are shown to the left and the corresponding Fourier transforms to the right. The fits were obtained with a coordination environment composed of 1 sulfur from cysteine, 2 nitrogens from histidine and 1 additional N/O donor (compare [21]).…”