CRYSTALLIZATION AND PRELIMINARY CRYSTALLOGRAPHIC ANALYSIS OF ANTISTASIN, A LEECH-DERIVED INHIBITOR OF BLOOD-COAGULATION FACTOR-XA

Abstract The salivary gland of the Mexican leech Haementeria officinalis contains a 15 kDa protein which is a potent and selective inhibitor of factor Xa. It inhibits not only blood coagulation, but also metastasis. A gene, coding for a sequence similar to published antistasin sequences, has been synthesized and expressed in Chinese hamster ovary (CHO) cells. The recombinant protein was purified and crystallized at pH 6·0, using 31% ammonium sulfate as a precipitant, the crystals diffract at least to 2·8 A. The spacegroup is I 422 with a = b = 77·7 A and c = 88·4 A. The crystals contain 42% solvent and one protein molecule in the asymmetric unit. A search for heavy atom derivatives is in progress.