Four data sets were collected from monoclinic crystals of the Leuconostoc mesenteroides D-alanine:D-lactate ligase. This 42.8 kDa enzyme is the agent of vancomycin resistance in many gram-positive bacteria. The enzyme crystallizes from PEG/ammonium sulfate in space group C2 with 2 molecules per asymmetric unit in a cell measuring 118x91x82? and ? = 92-. The data sets were collected with the ADSC detector on beamline A1 and included native data to 2.4 ?, 2.6 ? data from platinum tetrachloride and methyl mercury derivatives, and 2.7 ? data from a seleno-methionine derivative. The seleno data were collected to examine the diffraction quality of the seleno-met crystals prior to a full MAD data collection at a later date. All data were processed with the HKL package. Crystals of the ligase had high mosaicity greater than 1.5-; these crystals nevertheless gave reasonable Rmerge(I) values between 6.5 and 9.0%. The ligase structure is being solved by MIRAS, but a complete model has not yet been produced. It appears that another derivative will be needed to improve the electron density map. Chain tracing will be aided with the seleno-met data. Another crystal form has been found to grow more easily to larger size, and this new form can be used if necessary. Near the end of the 2-day run period we had time to collect a rather high resolution data set (1.8 ?) from a small ?-lactamase crystal which measured only 50x100 microns; Rmerge was 7.6%. This orthorhombic structure has been solved by MR and refined to an R factor of 21% for all data. This structure represents the first structure of a clinically-derived mutant of the ampC type chromosomal class C ?-lactamase. A manuscript is being prepared for publication.
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