Crystallization and atomic resolution X-ray diffraction analysis of antichymotrypsin variants

Abstract

Crystals of two recombinant antichymotrypsin (rACT) variants have been prepared: variant rACT-T345R crystallizes in space group P21 (a = 109.2 Å, b = 79.4 Å, c = 111.9 Å, β = 116.3°, with 2 molecules in the asymmetric unit), and variant ACT' crystallizes in space group P21221 (a = 69.7 Å, b = 77.2 Å, c = 83.8 Å, with one molecule in the asymmetric unit). The latter variant is an engineered dimer having the P3-P3′ hexapeptide sequence of the related serpin, α1-proteinase inhibitor, substituted for the corresponding wild-type sequence. Crystals of each variant diffract to a limiting resolution 2.5 Å, which represents the best diffraction yet achieved for a crystalline, inhibitory serpin. The exceptional quality of ACT crystals probably arises from favorable protein-protein interactions as well as a stabilizing disulfide crosslink engineered between the monomers. © 1993 Academic Press, Inc.