Nuclear Overhauser Effects And Circular Dichroism As Probes Of \beta.-turn Conformations In Acyclic And Cyclic Peptides With Pro-X Sequences

Content Provider	Indian Institute of Science (IISc)
Author	Rao, Narasinga Bn Kumar, Anil Balaram, Hemalatha Ravi, A. Balaram, P.
Copyright Year	1983
Abstract	Nuclear Overhauser effects (NOE) and (CD) techniques have been used to probe \beta-turn conformations in acyclic and cyclic peptides containing Pro-X sequences. The model peptides studied are of the type Piv-Pro-X-NHMe (X = Aib, D-Ala, Gly, Val, and Leu) and Boc-Cys-Pro-X-Cys NHMe (X = Aib, L-Ala, D-Ala, Gly, and Leu). In the acyclic series, observation of NOE's between Pro $C^\alphaH$ and X-NH, together with solvent and temperature dependence of NH chemical shifts, establishes a 4 \longrightarrow 1 hydrogen bond stabilized type I1 \beta-turn in the Gly, D-Ala, and Aib peptides, in $CDC1_3$ and $(CD_3)_2S0$. A positive $n-\pi^*$ CD band at \sim 225-230 nm appears to be characteristic of this structure. For the acyclic Pro-Leu peptide the observation of NOE's for both Pro and Leu $C^\alphaH$ resonances on saturation of Leu NH is compatible with a type V bend or consecutive \gamma-turn conformation. In the cyclic disulfide series the Pro-Aib and Pro-D-Ala peptides favor type I1 \beta-turns, whereas all other peptides adopt type I (111) conformations. All the cyclic disulfides exhibit an intense negative CD band at \sim 228-230 nm. The results suggest that general correlations between CD spectral type and specific \beta-turn conformations may not be obtained. Evidence for solvent-dependent structural changes in the Pro-Aib sequence in both cyclic and acyclic peptides is presented.
File Format	PDF
Journal	PeerReviewed
Language	English
Publisher	American Chemical Society
Publisher Date	1983-01-01
Access Restriction	Authorized
Subject Keyword	Molecular Biophysics Unit Physics
Content Type	Text
Resource Type	Article