Purification, crystallization and preliminary crystallographic analysis of the catalytic core of cystathionine β-synthase from Saccharomyces cerevisiae

Cystathionine beta-synthase (CBS; EC 4.2.1.22) catalyzes the condensation of homocysteine and serine to form cystathionine, with the release of water. In humans, deficiency in CBS activity is the most common cause of hyperhomo-cysteinaemia and homocystinuria. More than 160 pathogenic mutations in the human CBS gene have been described to date. Here, the purification and preliminary crystallographic analysis of the catalytic core of CBS from Saccharomyces cerevisiae (ScCBS) is described which, in contrast to other eukaryotic CBSs, lacks the N-terminal haem-binding domain and is considered to be a useful model for investigation of the pyridoxal-5'-phosphate- mediated reactions of human CBS (hCBS). The purified protein yielded two different crystal forms belonging to space groups P4(1)2(1)2 and P2(1)2(1)2(1), with unit-cell parameters a = b = 72.390, c = 386.794 angstrom and a = 58.156, b = 89.988, c = 121.687 angstrom, respectively. Diffraction data were collected to 2.7 and 3.1 angstrom resolution, respectively, using synchrotron radiation. Preliminary analysis of the X-ray data suggests the presence of ScCBS homodimers in both types of crystals.