Conformations of heterochiral and homochiral proline-pseudoproline segments in peptides: context dependent cis-trans peptide bond isomerization

Kantharaju, ; Raghothama, Srinivasarao ; Raghavender, Upadhyayula Surya ; Aravinda, Subrayashastry ; Shamala, Narayanaswamy ; Balaram, Padmanabhan (2009) Conformations of heterochiral and homochiral proline-pseudoproline segments in peptides: context dependent cis-trans peptide bond isomerization Peptide Science, 92 (5). pp. 405-416.

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Official URL: http://onlinelibrary.wiley.com/doi/10.1002/bip.212...

Related URL: http://dx.doi.org/10.1002/bip.21207

Abstract

The pseudoproline residue (ψPro, L-2,2-dimethyl-1,3-thiazolidine-4-carboxylic acid) has been introduced into heterochiral diproline segments that have been previously shown to facilitate the formation of β-hairpins, containing central two and three residue turns. NMR studies of the octapeptide Boc-Leu-Phe-Val-DPro-ψPro-Leu-Phe-Val-OMe (1), Boc-Leu-Val-Val-DPro-ψPro-Leu-Val-Val-OMe (2), and the nonapeptide sequence Boc-Leu-Phe-Val-DPro-ψPro-DAla-Leu-Phe-Val-OMe (3) established well-registered β-hairpin structures in chloroform solution, with the almost exclusive population of the trans conformation for the peptide bond preceding the ?Pro residue. The β-hairpin conformation of 1 is confirmed by single crystal X-ray diffraction. Truncation of the strand length in Boc-Val-DPro-ψPro-Leu-OMe (4) results in an increase in the population of the cis conformer, with a cis/trans ratio of 3.65. Replacement of ψPro in 4 by LPro in 5, results in almost exclusive population of the trans form, resulting in an incipient β-hairpin conformation, stabilized by two intramolecular hydrogen bonds. Further truncation of the sequence gives an appreciable rise in the population of cis conformers in the tripeptide Piv-DPro-ψPro-Leu-OMe (6). In the homochiral segment Piv-Pro-ψPro-Leu-OMe (7) only the cis form is observed with the NMR evidence strongly supporting a type VIa β-turn conformation, stabilized by a 4→1 hydrogen bond between the Piv (CO) and Leu (3) NH groups. The crystal structure of the analog peptide 7a (Piv-Pro-ψH,CH3Pro-Leu-NHMe) confirms the cis peptide bond geometry for the Pro-ψH,CH3Pro peptide bond, resulting in a type VIa β-turn conformation.

Item Type:Article
Source:Copyright of this article belongs to John Wiley and Sons.
Keywords:Pseudoproline; Peptides; cis-trans Isomerization; NMR; Turn
ID Code:91484
Deposited On:21 May 2012 12:54
Last Modified:21 May 2012 12:54

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