CRYSTAL STRUCTURE OF ACTIVE SERPIN FAMILY:

IMPLICATION FROM MANDUCA SEXTA SERPIN K AT 2.2Å RESOLUTION. Jinping Li, Haobo Jiang*, Michael R. Kanost*, & Elizabeth J. Goldsmith, Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75235-9050, *Department of Biochemistry, Kansas State University, Manhattan, KS 66506

Manduca sexta serpin K is a member of the serine protease inhibitor superfamily that inhibit the activity of chymotrypsin. Serpins are important protease inhibitors that are widely distributed not only in vertebrate blood plasma but also in invertebrate body fluid. Sequence alignment based on the crystal structure of cleaved form of (1-antitrypsin, indicates that the serpins share a common fold structure(Huber, R. and Carrell, R. W.). On cleavage of the reactive center peptide bond, they undergo a remarkable conformational change with the newly generated C-terminal moving 70Å apart to the opposite pole of the molecule. The structures of the cleaved form and the two intact forms (antithrombin and antichymotrypsin) are available, but many important aspects of the conformation of the active serpin and particularly that of their reactive center is still not clear. In this report, we have determined the structure of recombinant active serpin K from Manduca sexta by molecular replacement to 2.2 Å. The space group of this molecule is monoclinic C2. The high resolution structure of the active serpin K shows that its structure is similar to ovalbumin and reveals the possible interaction of serpin with their target proteases. The other significant feature of the Manduca Sexta serpins is that eleven variants of serpins which are encoded from the same gene by alternative pre-mRNA splicing have already been found and each of them has the identical sequence except C-terminal 40-45 amino acids including the reactive center loop. The different reactive center loops generate different inhibitor activities. This structure also implicates how the conformation of the reactive center determines its specificity.