Purification and preliminary X-ray crystallographic studies of beta-microseminoprotein from human seminal plasma.

beta-Microseminoprotein (beta-MSP) is a small cysteine-rich protein with a molecular mass of 10 kDa. It was first isolated from human seminal plasma and has subsequently been identified from several species. Comparison of the amino-acid sequences of beta-MSP proteins suggests that the protein is a rapidly evolving protein. The function of beta-MSP is poorly understood. Furthermore, no crystal structure has been reported of any beta-MSP; therefore, determination of the crystal structure of beta-MSP is the foremost task in order to understand the function of this protein completely. Here, the purification, crystallization and preliminary X-ray diffraction analysis of beta-MSP from human seminal plasma are described. The protein was purified using anion-exchange and size-exclusion chromatography and the purified protein was crystallized using 0.1 M ammonium sulfate, 0.1 M HEPES buffer pH 7.0 and 20%(w/v) PEG 3350. The crystals belonged to the tetragonal space group P4(3)22 and contained three beta-MSP molecules in the asymmetric unit. X-ray intensity data were collected to 2.4 A resolution.