A common precursor for a putative hemorrhagic protein and rhodostomin, a platelet aggregation inhibitor of the venom of Calloselasma rhodostoma: Molecular cloning and sequence analysis

Rhodostomin is a platelet aggregation inhibitor secreted by the venom gland of Calloselasma rhodostoma. We report here the isolation of a 1.67-kilobase (kb) λgt11 cDNA clone using degenerate oligonucleotide probe based on a partial amino acid sequence of rhodostomin. The amino acid sequence deduced from an open reading frame of the cDNA indicates that (i) the 68-amino acid sequence of rhodostomin is located at the carboxyl terminus of the precursor polypeptide and (ii) a peroxisomal targeting sequence (ser.his.ala.) exists between the stop codon and the rhodostomin sequence of the precursor. Since the amino-terminal segment of the deduced sequence shows a high degree of identity with hemorrhagic proteins, which are zinc-metalloproteinases, found in the venom of some crotalid and viperid snakes, our results also predict the existence of at least one such hemorrhagic protein in the venom of Calloselasma rhodostoma. The derivation of a platelet aggregation inhibitor and a hemorrhagic protein from the same precursor protein is consistent with the fact that these proteins may be synergistic in function.