H-1, C-13 AND N-15 RANDOM COIL NMR CHEMICAL-SHIFTS OF THE COMMON AMINO-ACIDS .1. INVESTIGATIONS OF NEAREST-NEIGHBOR EFFECTS

In this study we report on the H-1, C-13 and N-15 NMR chemical shifts for the random coil state and nearest-neighbor sequence effects measur ed from the protected linear hexapeptide Gly-Gly-X-Y-Gly-Gly (where X and Y are any of the 20 common amino acids). We present data for a set of 40 peptides (of the possible 400) including Gly-Gly-X-Ala-Gly-Gly and Gly-Gly-X-Pro-Gly-Gly, measured under identical aqueous conditions . Because all spectra were collected under identical experimental cond itions, the data from the Gly-Gly-X-Ala-Gly-Gly series provide a compl ete and internally consistent set of H-1, C-13 and N-15 random coil ch emical shifts for all 20 common amino acids. In addition, studies were also conducted into nearest-neighbor effects on the random coil shift arising from a variety of X and Y positional substitutions. Compariso ns between the chemical shift measurements obtained from Gly-Gly-X-Ala -Gly-Gly and Gly-Gly-X-Pro-Gly-Gly reveal significant systematic shift differences arising from the presence of proline in the peptide seque nce. Similarly measurements of the chemical shift changes occurring fo r both alanine and proline (i.e., the residues in the Y position) are found to depend strongly on the type of amino acid substituted into th e X position. These data lend support to the hypothesis that sequence effects play a significant role in determining peptide and protein che mical shifts.