REFINED CRYSTAL-STRUCTURE OF ACINETOBACTER GLUTAMINASIFICANS GLUTAMINASE ASPARAGINASE

The crystal structure of glutaminase-asparaginase from Acinetobacter glutaminasificans has been reinterpreted and refined to an R factor of 0.171 at 2.9 Angstrom resolution, using the same X-ray diffraction data that were used to build a preliminary model of this enzyme [Ammon, Weber, Wlodawer, Harrison, Gilliland, Murphy, Sjolin and Roberts (1988). J. Biol. Chem. 263, 150-156]. The current model, which does not include solvent, is based in part on the related structure of Escherichia coli asparaginase and is significantly different from the structure of the enzyme from A. glutaminasificans described previously. The reason for the discrepancies has been traced to insufficient phasing power of the original heavy-atom derivative data, which could not be compensated for fully by electron-density modification techniques. The corrected structure of A. glutaminasificans glutaminase-asparaginase is presented and compared with the preliminary model and with the structure of E. coli asparaginase.