SEQUENCE-CORRECTED N-15 RANDOM COIL CHEMICAL-SHIFTS

The N-15 chemical shifts in a group of oligopeptides H-Gly 1-Gly Z-Xxx 3-Ala 4-OH, where Xxx stands far one of the 20 proteinogenic amino acid residues, were measured using two-dimensional heteronuclear single-quantum coherence (HSQC) experiments. Following the hypothesis, based on earlier observations, that the ''random coil'' N-15 shifts are predominantly determined by the chemical structures of the residue considered and the preceding residue in the sequence, we evaluated the influence of the residue type in position 3 on the N-15 chemical shift of Ala 4 in the above peptides. These data were combined with the N-15 chemical shifts for the 20 common amino acid residues measured in position 3 of the same peptides to calculate the 400 ''random coil'' reference shifts for the 20 amino acid residues Xxx in ail possible dipeptide sequences Yyy-Xxx. Chemical shift predictions based on this data set fit experimental N-15 shifts in denatured proteins within a range of +/-2 ppm and, thus, represent a useful reference for investigations on correlations between N-15 chemical shifts and polypeptide conformation.