CONFORMATIONAL PROPERTIES OF 4 PEPTIDES CORRESPONDING TO ALPHA-HELICAL REGIONS OF RHODOSPIRILLUM CYTOCHROME C(2) AND BOVINE CALCIUM-BINDING PROTEIN

Four peptides corresponding to alpha-helical regions delimited by residues 63-73 and 97-112 of cytochrome c(2) (Rhodospirillum) and residues 24-36 and 45-55 of bovine calcium binding protein are predicted to be alpha-helical by a recently developed method [Rooman, M., Kocher, J. P., & Wodak, S. J. (1991) J. Mol. Biol. 221, 961-979], synthesized by solid phase methods, and purified by HPLC, and their solution conformations are determined by NMR and CD. The observed conformational properties of these peptides in solution confirmed prediction results: in water/TFE (60/40, v/v) at room temperature, these peptides adopt an alpha-helical conformation, as shown by an extended pattern of strong, sequential d(NN)(i,i+1) NOE cross-peaks, d(alpha N)(i,i+1) NOEs of reduced intensity, several medium-range [d(alpha N)(i,i+3), d(alpha N)(i,i+4), d(alpha beta)-(i,i+3)] NOE connectivities, small (3)J(H alpha N) values, and more upfield alpha-proton chemical shifts. CD studies at different TFE concentrations and at room temperature provide further evidence of the propensity of these peptides to adopt an alpha-helical conformation in solution, as determined by the ellipticity values at 222 nm, and by deconvolution of the CD spectra. According to the method used, helicities in the range 34-50% and 55-75% are found for the 63-73 and 97-112 fragments of cytochrome c(2), respectively, and in the range 53-80% and 42-65% for the fragments 24-36 and 45-55 of calcium binding protein in water/TFE (60/40, v/v) at 298 K. In addition, the experiments and predictions agree for those residues that are more flexible. Finally, the relevance of our results for the protein folding pathways is discussed.