An investigation into the N- and C-capping effects of glycine in cavitand-based four-helix bundle proteins

The capping efficiency of glycine on cavitand-based synthetic four-helix bundles was investigated. Glycine, a common C-capping amino acid, has always been included as a C-terminal residue in our de novo peptides, although the exact contribution of the glyince cap to the overall stability and structure of the caviteins had not previously been examined. The uncapped proteins were found to be less helical according to their CD spectra. In addition, the H/D exchange experiments suggested that the uncapped caviteins were more conformationally flexible. Capped and uncapped caviteins exhibited similar values of unfolding. Overall, it can be concluded that glycine caps are useful, as they reduce helical unravelling and enhance helicity, and thus, glycine will be included as a C-terminal residue in future de novo peptide sequences.