Crystal Structure of Escherichia coZi TEMl P-Lactamase at 1.8 A Resolution

Abstract : The X-ray structure of E8-cherichia coZi TEMl p-lactamase has been refined to a crystallographic R-factor of 16.4% for 22,510 reflections between 5.0 and 1.8 A resolution ; 199 water molecules and 1 sulphate ion were included in refinement. Except for the tips of a few solvent-exposed side chains, all protein atoms have clear electron density and refined to an average atomic temperature factor of 11 A2. The estimated coordinates error is 0.17 A. The substrate binding site is located at the interface of the two domains of the protein and contains 4 water molecules and the sulphate an-ion. One of these solvent molecules is found at hydrogen bond distance from S70 and E166. S70 and 5130 are hydrogen bonded to K73 and K234, respectively. It was found that the E. coZi TEMl and Staphylococcus aureus PC1 p-lacta-mases crystal structures differ in the relative orientations of the two domains composing the enzymes, which result in a narrowed substrate binding cavity in the TEMl enzyme. Local but significant differences in the vicinity of this site may explain the occurrence of TEMl natural mutants with extended substrate specificities.