CRYSTAL-STRUCTURE OF CLEAVED HUMAN ALPHA-1-ANTICHYMOTRYPSIN AT 2.7-A RESOLUTION AND ITS COMPARISON WITH OTHER SERPINS

The crystal structure of proteolytically modified human α1-antichymotrypsin (ACT), a member of the serpin superfamily, has been solved by Paterson search techniques and refined to an R-factor of 18.0% at 2.7 Å resolution with mean deviations from standard bond lengths and angles of 0.013 Å and 3.1 °, respectively. The final model consists of 374 amino acid residues, 126 solvent molecules and five sugar residues. Asn70 could be identified unambiguously as a glycosylation site and Asn104 is probably also glycosylated. The structure of cleaved ACT is compared with cleaved α1-antitrypsin (α1PI) and with plakalbumin, which are prototypical models for cleaved and intact serpins, respectively. Cleaved ACT is very similar to cleaved α1PI: in particular, it has strand s4A, which is liberated by proteolysis, inserted as the middle strand in β-sheet A. ACT and α1PI differ locally only at sites of insertions, except at the segment s3C-turn-s4C, which is displaced by several ångström units. This region of ACT is involved in DNA binding. © 1991.