Crystallization and preliminary X‐ray crystallographic analysis of the oxysterol‐binding protein Osh3 from Saccharomyces cerevisiae

Oxysterol‐binding protein (OSBP) related proteins (ORPs) are conserved from yeast to humans and are implicated in regulation of sterol homeostasis and in signal transduction pathways. Osh3 of Saccharomyces cerevisiae is a pleckstrin‐homology (PH) domain‐containing ORP member that regulates phosphoinositide metabolism at endoplasmic reticulum–plasma membrane contact sites. The N‐terminal PH domain of Osh3 was purified and crystallized as a lysozyme fusion and the resulting crystal diffracted to 2.3 Å resolution. The crystal belonged to the monoclinic space group C 2, with unit‐cell parameters a = 98.03, b  = 91.31, c = 84.13 Å, β = 81.41°. With two molecules in the asymmetric unit, the Matthews coefficient was 3.13 Å 3  Da −1 . Initial attempts to solve the structure by molecular‐replacement techniques using T4 lysozyme as a search model were successful. The C‐terminal OSBP‐related domain (OBD) of Osh3 was crystallized by the vapour‐diffusion method and the resulting crystal diffracted to 1.5 Å resolution. The crystal was orthorhombic, belonging to space group P 2 1 2 1 2 1 , with unit‐cell parameters a = 41.57, b = 87.52, c = 100.58 Å. With one molecule in the asymmetric unit, the Matthews coefficient was 2.01 Å 3  Da −1 . Initial attempts to solve the structure by the single‐wavelength anomalous dispersion technique using bromine were successful.