Chemical shifts in denatured proteins: Resonance assignments for denatured ubiquitin and comparisons with other denatured proteins

Chemical shift assignment is reported for the protein ubiquitin denatured in 8M urea at pH 2. The variations in ¹⁵N chemical shifts of three different proteins (ubiquitin, disulfide reduced, carboxymethylated lysozyme, all-Ala--lactalbumin), all without disulfides and denatured in 8M urea at pH 2 are compared to `random coil shifts' of small model peptides (Braun et al., 1994) and to the averaged native chemical shifts taken from the BMRB database. Both parameterizations show a remarkable agreement with the averaged measured ¹⁵N chemical shifts in the three denatured proteins. Detailed analysis of these experimental ¹⁵N chemical shifts provides an estimate of the influence of nearest neighbors and conformational preferences on the chemical shift and provides a direct means to identify non-random structural preferences in denatured proteins.