Helicogenic amino acids

The a-helix is one of the best-known regular conformational features as a subheading within the secondary structure of polypeptides and is frequently adopted in chains of six or more helicogenic amino acids (see Table 2.1 for a definition of terms and examples). The (3-sheet is another classic conformational structure that has been detected from the earliest days of X-ray crystallography of proteins. Local... 

Hinds et al.[26 used a helicogenic Ca-alkylproline derivative 271 in the peptide Ac-Tyr-Pro-Tyr-Asp-Val-Pro-Asp-Tyr-Ala-OH, which is derived from an immunogenic sequence in influenza hemagglutinin, specifically replacing the first Pro residue in the sequence. They found increased binding to a pair of monoclonal antibodies which recognize this site. 26 The insertion of C -alkyl a-amino acids into peptide systems is discussed in Section 10.3. 

This is characterized by the presence of two TOAC nitroxide free radicals at relative position i, i + 3, which together with Aib represent two of the strongest helicogenic, C -tetrasubstituted, a-amino acids. In their work, Carlotto et al. [97] compared the experimental CW-ESR spectra with the theoretical counterpart pertaining to the 3io and a-helix minima obtained by QM computations and unraveled the solvent-driven equilibria between the two conformations. 

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