DETERMINATION OF DISULFIDE BRIDGE PATTERN IN OMEGA-CONOPEPTIDES

Synthetic versions of seven naturally occurring omega-conopeptides wer e subjected to structural analyses in order to determine their disulfi de bridge pattern. The method applied in this study uses a combination of amino-acid composition and peptide sequence analysis of various pe ptide fragments generated by different enzymatic digestions. A tempera ture modification in the Edman degradation cycles of a protein sequenc er allowed the unambiguous detection of the cleavage of cystine residu es. The appearance of the cystine residues in particular cycles of the sequence analysis was characteristic of one or several of the theoret ically possible 15 isomers. In the case of multiple choices, possible isomers were further eliminated by the amino-acid and sequence analysi s of peptide fragments generated by the enzymatic digestion. All synth etic peptides, SNX-111, -157, -159, -183, -185, -230 and -231, were fo und to have the same disulfide bridge pattern as determined for the na turally occurring omega-conopeptide G-VI-A, i.e. disulfide bridges bet ween the half-cystines 1-16, 8-20 and 15-25 (using the amino-acid numb ering of SNX-111). (C) Munksgaard 1995.