Structure of the SHV-1 β-Lactamase

Abstract

The X-ray crystallographic structure of the SHV-1 β-lactamase has been established. The enzyme crystallizes from poly(ethylene glycol) at pH 7 in space group P2₁2₁2₁ with cell dimensions a = 49.6 Å, b = 55.6 Å, and c = 87.0 Å. The structure was solved by the molecular replacement method, and the model has been refined to an R-factor of 0.18 for all data in the range 8.0−1.98 Å resolution. Deviations of model bonds and angles from ideal values are 0.018 Å and 1.8°, respectively. Overlay of all 263 α-carbon atoms in the SHV-1 and TEM-1 β-lactamases results in an rms deviation of 1.4 Å. Largest deviations occur in the H10 helix (residues 218−224) and in the loops between strands in the β-sheet. All atoms in residues 70, 73, 130, 132, 166, and 234 in the catalytic site of SHV-1 deviate only 0.23 Å (rms) from atoms in TEM-1. However, the width of the substrate binding cavity in SHV-1, as measured from the 104−105 and 130−132 loops on one side to the 235−238 β-strand on the other side, is 0.7−1.2 Å wider than in TEM-1. A structural analysis of the highly different affinity of SHV-1 and TEM-1 for the β-lactamase inhibitory protein BLIP focuses on interactions involving Asp/Glu104.