Isolation of cDNA encoding a novel serpin of crayfish hemocytes

We have cloned a serpin-type proteinase inhibitor from a crayfish hemocyte cDNA library. The deduced amino acid sequence consists of 429 amino acids with a putative signal peptide of 21 amino acids. The mature protein has a calculated molecular mass of 45,029 daltons. Identities ranging up to 38% were observed between the crayfish serpin and other members of the serpin family. Phylogenetic analysis shows that the crayfish serpin has a closer relationship to insect serpins than to other animal serpins. Phe369-Ser370 were proposed to be the P1-P1' residues of the inhibitor reactive site. This protein was found to be expressed in hemocytes but not in the hepatopancreas of the crayfish Pacifastacus leniusculus.