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

A unique serine-protease inhibitor (serpin) of the blood fluke S. haematobium has been crystallized. It is an antitrypsin with an unusual residue (phenylalanine) at its reactive center. Unlike any known member of this gene family, 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 may play a important role in host–parasite interaction. The crystals belong to the trigonal space group P3₂21 or P3₁21 with unit-cell parameters a = b = 64.7, c = 186.7 Å, α = 90.0, β = 90.0, γ = 120.0°. There is one molecule per asymmetric unit and the crystals diffracted to 2.2 Å.