J. Biol. Chem., Vol. 255, Issue 17, 8266-8272, 09, 1980
Structure and action of heteronemertine polypeptide toxins. Primary structure of Cerebratulus lacteus toxin A-III
KM Blumenthal and WR Kem
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.
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