CRYSTAL-STRUCTURE OF H-2-PROTEINASE FROM THE VENOM OF TRIMERESURUS-FLAVOVIRIDIS

The crystal structure of the zinc-protease, H-2-proteinase, isolated f rom the venom of Trimeresurus flavoviridis has been determined. The cr ystallographic R factor is 0.176 for 10,635 reflections with F-obs > 2 sigma (F-obs) in the 8.0 to 2.2 Angstrom resolution range. The enzyme has two domains with a cleft in which a catalytic zinc atom is locate d. The N-terminal domain is composed of four helices around a central five-stranded beta-sheet. The irregularly folded C-terminal domain con tains one helix and two disulfide bridges. These two domains are linke d by a disulfide bridge. In the zinc environment, the catalytic zinc a tom forms a distorted tetrahedral coordination with three histidines a nd one catalytic water molecule, and the methionine-containing turn is structurally conserved. These are distinctive features of the metzinc ins, one of the zinc metalloprotease superfamilies. The entire structu re shows good agreement with that of two Crotalus snake venom protease s, adamalysin II and atrolysin C. The H-2-proteinase, however, contain s no structural calcium ions, and differences of disulfide configurati ons and the coordination of the catalytic water molecule exist as comp ared with the other two proteases.