Structure of the low molecular weight protein copurified with alpha-latrotoxin

Some samples of latrotoxin purified from the black widow spider venom contain two components: alpha-latrotoxin (M(r) approximately 130,000) and a low mol. wt protein with M(r) about 8000. Clones carrying the cDNA sequence for the low mol. wt protein copurified with alpha-latrotoxin were isolated from spider venom glands. Nucleotide sequence analysis of the cloned cDNA revealed the primary structure of the polypeptide to be 18 amino acids signal peptide and 70 amino acids protein chain with mol. wt of 7947 and pI of approximately 4.0. The protein exhibits certain structural homology with erabutoxin-a from the sea snake.