Snake fetuin: isolation and structural analysis of new fetuin family proteins from the sera of venomous snakes.

Novel proteins were isolated from the sera of Chinese Mamushi (Gloydius blomhoffi brevicaudus) and Habu (Trimeresurus flavoviridis). The primary structures of these proteins were determined by protein sequencing, and the nucleotide sequences were established by cDNA cloning from the liver mRNAs. They belonged to the fetuin family having a double-headed cystatin-like domain and a His-rich domain, akin to HSF, an antihemorrhagic factor isolated from Habu serum. They showed no antihemorrhagic activity and were designated HSF-like proteins (HLPs). Mamushi serum contained two different HLPs termed HLP-A and HLP-B. Both HLP-A and Habu HLP had a unique 17-residue deletion in their His-rich domains. HLP-B comprised two glycosylated polypeptide chains and inhibited the precipitation of calcium phosphate as potently as does bovine fetuin. HLP-B was hence identified as a snake fetuin. The phylogenetic analysis of the fetuin family of proteins showed that antihemorrhagins and HLPs have evolved from this snake fetuin.