Comparison between the Backbone Dynamics of an 11-Amino Acid Peptide Sequence in α-Helical and β-Hairpin Structural Contexts.

To investigate the relationship between backbone motions and the structural environment of a peptide sequence, we have used 15N NMR relaxation data to characterize the backbone motions of the ‘chameleon-α’ (Chm-α) and ‘chameleon-β’ (Chm-β) proteins designed previously by Minor and Kim [Minor, D. L., Jr., and Kim, P. S. (1996) Nature 380, 730–734]. These two proteins contain an identical 11-amino acid sequence (dubbed the ‘chameleon’ peptide sequence) in α-helix and β-hairpin conformations, respectively, within the B1 domain of protein G. When placed in an α-helical context, the chameleon peptide shows very limited backbone motions, but some remote regions of the protein are induced to undergo conformational exchange motions, apparently due to modification of packing interactions with the chameleon peptide. In contrast, within a β-hairpin context, the chameleon peptide displays substantial motions on both picosecond and microsecond-to-millisecond time scales, suggesting that it cannot be readily accommodated within the native reverse turn structure. These observations are consistent with the relatively low stability of the Chm-β protein and can be rationalized in terms of native turn-stabilizing interactions that may be disrupted in the Chm-β protein. [ABSTRACT FROM AUTHOR]