Purification and characterization of huwentoxin-II, a neurotoxic peptide from the venom of the Chinese bird spider Selenocosmia huwena

A neurotoxic peptide, huwentoxin-II (HVVTX-II), was purified from the venom of the Chinese bird spider Selenocosmia huwena by ion exchange chromatogra phy and reversed phase HPLC. The toxin can reversibly paralyse cockroaches for several hours, with an ED50 of 127 +/- 54 mu g/g. HWTX-II blocks neurom uscular transmission in an isolated mouse phrenic nerve diaphragm preparati on and acts cooperatively to potentiate the activity of huwentoxin-I. The c omplete amino sequence of HWTX-II was determined and found to consist of 37 amino acid residues, including six Cys residues. There is microheterogenei ty (Ile/Gln) in position 10, and mass spectrometry indicated that the two i soproteins have a tendency to dimerize. It was determined by mass spectrome try that the six Cys residues are involved in three disulphide bonds. The s equence of HWTX-II is highly homologous with ESTX, a toxin from the tarantu la Eurypefina californicum.