The effects of guanidine hydrochloride on the 'random coil' conformations and NMR chemical shifts of the peptide series GGXGG.

The effects of the commonly used denaturant guanidine hydrochloride(GuHCl) on the random coil conformations and NMR chemical shifts of theproteogenic amino acids have been characterized using the peptide seriesAc-Gly-Gly-X-Gly-Gly-NH(2). The phi angle-sensitive couplingconstants, ROESY cross peak intensities and proline cis-trans isomerratios of a representative subset of these peptides are unaffected by GuHCl,which suggests that the denaturant does not significantly perturb intrinsicbackbone conformational preferences. A set of(3)J(HNHalpha) values is presented which agreewell with predictions of recently developed models of the random coil. Wehave also measured the chemical shifts of all 20 proteogenic amino acids inthese peptides over a range of GuHCl concentrations. The shifts exhibit alinear dependence on denaturant concentration and we report here correctionfactors for the calculation of 'random coil' (1)H chemicalshifts at any arbitrary denaturant concentration. Studies of arepresentative subset of peptides indicate that (13)C and(15)N chemical shifts are also perturbed by the denaturant.These results should facilitate the application of chemical shift-basedanalytical techniques to the study of polypeptides in solution with GuHCl.The effects of the denaturant on the quality of NMR spectra and on chemicalshift referencing are also addressed.