SOLUTION CONFORMATIONAL DYNAMICS OF THE C-TERMINAL RESIDUES IN ENDOTHELIN-1 AND SOME ANALOGS - A TIME-RESOLVED FLUORESCENCE STUDY

The rotational relaxation times of the single tryptophan residues in e ndotherlin-1, [Ala(1,3,11,15)]endothelin-1, human pro-endothelin-1, th e linear hexapeptide Ac-His-Leu-Asp-Ile-Ile-Trp which corresponds to t he C-terminal residues 16-21 in endothelin-1, the cyclic pentapeptide BQ123, and several di- and tri-peptides possessing C-terminal tryptoph an residues have been determined from time-resolved fluorescence aniso tropy decays obtained by phase/modulation techniques. Fluorescence lif etime distribution widths have also been examined as predictors of con formational heterogeneity/restriction. A significant contribution from a slow rotational component supports either the persistence, on the n anosecond timescale al least, of a non-flexible alpha-helical structur e for the C-terminal tail residues of endothelin-1 in water as solvent , as seen in the X-ray crystallographic structure, or the interaction of the C-terminal tail residues 16-21 with the constrained disulfide-b ridged core residues 1-15. This slow rotational contribution is less e vident in the linear, acyclic tetraalanine analogue but greatly increa sed in pro-endothelin-1. In BQ123 the fluorescence characteristics sup port the occurrence of a dominant rotameric form involving the indole sidechain of the D-tryptophan residue (C-alpha-C-beta torsion angle ch i(1) of 60 degrees, as previously determined by NMR). (C) Munksgaard 1 995.