title: Structure and action of heteronemertine polypeptide toxins. Primary structure of Cerebratulus lacteus toxin A-III.
abstract: The primary structure of Cerebratulus lacteus cytotoxin A-III has been determined by automated Edman degradation of the reduced, carboxymethylated protein and of peptides derived therefrom by hydrolysis with trypsin and staphylococcal protease. As a result of these studies, the positions of all 95 amino acid residues have been determined unambiguously. The COOH-terminal half of the protein is more hydrophobic than is the NH2-terminal half. The predicted secondary structure of toxin A-III contains 38% alpha helix and 14% beta sheet, in excellent agreement with the values obtained experimentally by circular dichroism spectropolarimetry. Virtually all of the predicted helix lies in a single long stretch starting at position 63, just beyond the last residue of half-cystine in the sequence. This region of helix is also the most hydrophobic portion of the protein and may be involved in the mechanism of its cytotoxic action.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003603:Cytotoxins; D010450:Endopeptidases; D007448:Invertebrates; D008387:Marine Toxins; D010446:Peptide Fragments / Q000032:analysis; D010455:Peptides; D011487:Protein Conformation; D014357:Trypsin
chemical_list: C026601:Cerebratulus lacteus toxin A-III; D003603:Cytotoxins; D008387:Marine Toxins; D010446:Peptide Fragments; D010455:Peptides; D010450:Endopeptidases; D014357:Trypsin