VCD Spectroscopic Analysis of the Exendin-4 Truncated Analog TC5b

摘要

Truncation and residue replacements of the peptide exendin-4 with the goal of creating the smallest self-folding protein yielded the 20-residue "miniprotein" TC5b (Asn-Leu-Tyr-Ile-Gln-Trp-Leu-Lys-Asp-Gly-Gly-Pro-Ser-Ser-Gly-Arg-Pro-Pro-Pro-Ser). The folding and resulting tertiary structure of TC5b, unique for a sequence of its length, is a product of its 'Trp-cage' motif, which is formed through CH-pi interactions between Trp6 and Prol2, 18, and 19, as well as some crucial hydrogen bonds. TC5b has been the subject of much computational analysis and some spectroscopic analysis. Electronic circular dichroism spectroscopy (ECD) has shown that this peptide appears to be primarily alpha-helical in 30% TFE, as well as in aqueous and phosphate buffer. However, NMR has also shown the existence of a poly-Pro II helix associated with the C-terminal region. The poly-Pro II helix is not apparent in the ECD spectrum, but it may be possible to resolve it using vibrational circular dichroism spectroscopy (VCD). In the present study, VCD spectroscopy was used to examine the conformation of TC5b in a variety of deuterated aqueous and organic solvents. The observed spectra were compared to VCD spectra of poly-L-Pro (av. MW: 8900 Da) in deuterated aqueous and organic solvents.