THE EFFECT OF N-TERMINAL ACETYLATION ON THE STRUCTURE OF AN N-TERMINAL TROPOMYOSIN PEPTIDE AND ALPHA-ALPHA-TROPOMYOSIN

We have used a synthetic peptide consisting of the first 30 residues o f striated muscle alpha-tropomyosin, with GlyCys added to the C-termin us, to investigate the effect of N-terminal acetylation on the conform ation and stability of the N-terminal domain of the coiled-coil protei n. In aqueous buffers at low ionic strength, the reduced, unacetylated 32mer had a very low alpha-helical content (approximately 20%) that w as only slightly increased by disulfide crosslinking or N-terminal ace tylation. Addition of salt (> 1 M) greatly increased the helical conte nt of the peptide. The CD spectrum, the cooperativity of folding of th e peptide, and sedimentation equilibrium ultracentrifugation studies s howed that it formed a 2-chained coiled coil at high ionic strength. D isulfide crosslinking and N-terminal acetylation both greatly stabiliz ed the coiled-coil a-helical conformation in high salt. Addition of et hanol or trifluoroethanol to solutions of the peptide also increased i ts alpha-helical content. However, the CD spectra and unfolding behavi or of the peptide showed no evidence of coiled-coil formation. In the presence of the organic solvents, N-terminal acetylation had very litt le effect on the conformation or stability of the peptide. Our results indicate that N-terminal acetylation stabilizes coiled-coil formation in the peptide. The effect cannot be explained by interactions with t he ''helix-dipole'' because the stabilization is observed at very high salt concentrations and is independent of pH. In contrast to the resu lts with the peptide, N-terminal acetylation has only small effects on the overall stability of tropomyosin.