Characterization and crystallization of a novel Sarcocystis muris lectin, SML-2

A novel lectin (SML-2) consisting of 138 amino acids was isolated from cyst merozoites of Sarcocystis muris and sequenced by Edman degradation and mas s spectrometry. All 12 cysteinyl residues are involved in disulfide bridges , four of which are attributed to a characteristic pattern of cysteines as found in the so-called PAN-module superfamily. Crystals of SML-2 diffractin g to 2.1 Angstrom resolution at a synchrotron were grown by the hanging-dro p vapour-diffusion technique. They belong to the space group P2(1)2(1)2(1), with unit-cell parameters a = 53.6, b = 128.8, c = 158.2 Angstrom and eigh t molecules in the asymmetric unit. SML-2 cocrystallized with Au galactose results in two different crystal forms. The first form is isomorphous with the native crystals and the second form adopts space group C222(1), with un it-cell parameters a = 74.7, b = 82.0, c = 131.0 Angstrom, and diffracts to 2.4 Angstrom at a rotating-anode X-ray generator.