Conformational studies of peptide heart stimulant anthopleurin A. Laser Raman, circular dichroism, fluorescence...

Sea anemone contain a number of closely related peptide heart stimulants. In the present investigation, the conformation of anthropleurin A from Anthopleura xanthogrammica was investigated by laser Raman, circular dichroism, and fluorescence spectral methods and by the Chou-Fasman method using sequence data. The recent 13C NMR data of the peptide (Norton, R.S., and Norton, T.R. (1979) J. Biol. Chem., in press) provided useful information for the interpretation of the above-mentioned spectral data. The results from these spectral methods suggested that anthropleurin A and the related sea anemone peptides are roughly spherical in shape due to the presence of some beta-bends, possibly due to a beta-pleated sheet region and due to the 3 cystine residues in the peptide which exist in the gauche-gauche-gauche configuration. The sole tyrosine residue is exposed to the solvent, a finding which has now been confirmed by 13C NMR. The laser Raman and fluorescence spectral procedures showed that one or more of the tryptophan residues are buried. Interestingly, the reduction of the native protein with dithioerythritol did not change the spherical shape even in the presence of 5 M guanidine HCl and the carboxymethylcysteine derivative of the peptide was folded even in the presence of the denaturing agent, guanidine HCl.