Purification and crystallization of a novel membrane-anchored protein: theSchistosoma haematobium serpin

A unique serine-protease inhibitor (serpin) of the blood fluke S. haematobi um has been crystallized. It is an antitrypsin with an unusual residue (phe nylalanine) at its reactive center. Unlike any known member of this gene fa mily, it is a membrane-anchored protein on the surface of the parasite. The location of this serpin and immunological response to the protein indicate that it map play a important role in host-parasite interaction. The crysta ls belong to the trigonal space group P3(2)21 or P3(1)21 with unit-cell par ameters a = b = 64.7, c = 186.7 Angstrom, alpha = 90.0, beta = 90.0, gamma = 120.0 degrees. There is one molecule per asymmetric unit and the crystals diffracted to 2.2 Angstrom.