Crystallization and preliminary crystallographic analysis of phosphonoacetaldehyde hydrolase

Phosphonoacetaldehyde hydrolase, a C-P bond-cleaving enzyme which utilizes an unusual bicovalent catalytic strategy, has been crystallized by the hang ing-drop vapor-diffusion method using PEG 4000 as the precipitant. The crys tals belong to the monoclinic system and belong to space group C2, with uni t-cell parameters a = 210.5, b = 45.5, c = 64.7 Angstrom, beta = 105.0 degr ees. The asymmetric unit contains a dimer related by a non-crystallographic dyad. In addition to a 2.7 Angstrom native data set, the following data se ts have been collected: a 2.4 Angstrom data set from crystals complexed wit h the intermediate analog vinyl sulfonate, a 3.0 Angstrom three-wavelength MAD data set from crystals complexed with the product analog WO42-, as well as several heavy-atom data sets to 3.0 Angstrom or better, of which only t hree have proven useful for MIR calculations. Examination of the native Pat terson map revealed NCS that made previously uninterpretable derivative dat a useful. Independent phase sets were first calculated and refined for the MAD and MIR experiments separately and were then combined. The combined pha se set was further improved by solvent flattening, histogram matching and N CS averaging. Interpretation of the resulting electron-density map is curre ntly under way.