Expression, purification, crystallization and preliminary crystallographic analysis of phosphoserine aminotransferase from Bacillus alcalophilus

Phosphoserine aminotransferase (PSAT; EC 2.6.1.52) from Bacillus alcalophilus, an obligatory alkalophile with optimum growth at pH 10.6, was overexpressed in Escherichia coli, purified and crystallized under two different conditions using the hanging-drop vapour-diffusion method. Crystals were obtained using trisodium citrate dihydrate or PEG 400 as a precipitating agent. Crystals grown in the presence of trisodium citrate belong to the orthorhombic space group C222₁, with unit-cell parameters a = 105.6, b = 136.6, c = 152.0 Å, and those grown in the presence of PEG 400 belong to the orthorhombic space group P2₁2₁2, with unit-cell parameters a = 143.7, b = 84.3, c = 67.4 Å. Complete data sets were collected to 1.7 and 1.6 Å resolution, respectively, at 100 K using synchrotron radiation. Analysis of the structure of B. alcalophilus PSAT may reveal structural features that contribute to enzyme adaptability at high pH values.