Preferred conformations of protected homo-oligo-L-glutamate peptides in CDCl3 and CDCl3/TFA mixtures
✍ Scribed by Anthony Ribeiro; Robert P. Saltman; Murray Goodman
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1980
- Tongue
- English
- Weight
- 941 KB
- Volume
- 19
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Synopsis
A conformational analysis of protected glutamate homo-oligopeptides 2-[Glu(OEt)],-OEt (n = 2-7) was carried out in chloroform solution using high-resolution 'H-nmr spectroscopy.
At dilute peptide concentrations, the backbone NH and a-CH resonances are well resolved and can be assigned by combining extensive homonuclear decoupling experiments with data for co-oligopeptide derivatives. The structure of these peptides in solution was then assessed using information from chemical shifts, coupling constants, temperature coefficients, and titration of each oligomer with trifluoroacetic acid (TFA). The di-and tripeptides are found to be in disordered forms in deuterochloroform (CDC13) and CDCls/TFA mixtures. The tetrapeptide exhibits a folded structure with intramolecular hydrogen bonding at Glu2 in CDC13 and undergoes a transition to increasingly disordered forms as TFA is added. The pentamer to heptamer show a folded structure with a strong intramolecular hydrogen bond a t Glu2 and a weaker hydrogen bond at Glu3, which are disrupted as these peptides go to random coils a t high TFA/CDC13 ratios. In addition, the N-terminal portions of these glutamate peptides appear to be involved in side chain-main chain interactions. The results support the hypothesis that protected linear homo-oligopeptides may possess two or more segments of conformation with intramolecular folding preferred near the N-terminal portion.