Collagen Stability: Insights from NMR Spectroscopic and Hybrid Density Functional Computational Investigations of the Effect of Electronegative Substituents on Prolyl Ring Conformations
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- 作者：Michele L. DeRider ; Steven J. Wilkens ; Michael J. Waddell ; Lynn E. Bretscher ; Frank Weinhold ; Ronald T. Raines ; and John L. Markley
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：March 20, 2002
- 年：2002
- 卷：124
- 期：11
- 页码：2497 - 2505
- 全文大小：164K
- 年卷期：v.124,no.11(March 20, 2002)
- ISSN：1520-5126
文摘
Collagen-like peptides of the type (Pro-Pro-Gly)10 fold into stable triple helices. An electron-withdrawing substituent at the H
3 ring position of the second proline residue stabilizes these triple helices.The aim of this study was to reveal the structural and energetic origins of this effect. The approach was toobtain experimental NMR data on model systems and to use these results to validate computational chemicalanalyses of these systems. The most striking effects of an electron-withdrawing substituent are on the ringpucker of the substituted proline (Proi) and on the trans/cis ratio of the Xaai-1-Proi peptide bond. NMRexperiments demonstrated that N-acetylproline methyl ester (AcProOMe) exists in both the C-endo andC-exo conformations (with the endo conformation slightly preferred), N-acetyl-4(R)-fluoroproline methylester (Ac-4R-FlpOMe) exists almost exclusively in the C-exo conformation, and N-acetyl-4(S)-fluoroprolinemethyl ester (Ac-4S-FlpOMe) exists almost exclusively in the C-endo conformation. In dioxane, the Ktrans/cisvalues for AcProOMe, Ac-4R-FlpOMe, and Ac-4S-FlpOMe are 3.0, 4.0, and 1.2, respectively. Densityfunctional theory (DFT) calculations with the (hybrid) B3LYP method were in good agreement with theexperimental data. Computational analysis with the natural bond orbital (NBO) paradigm shows that thepucker preference of the substituted prolyl ring is due to the gauche effect. The backbone torsional angles,
and 
, were shown to correlate with ring pucker, which in turn correlates with the known and anglesin collagen-like peptides. The difference in Ktrans/cis between AcProOMe and Ac-4R-FlpOMe is due to an n
* interaction associated with the Bürgi-Dunitz trajectory. The decrease in Ktrans/cis for Ac-4S-FlpOMecan be explained by destabilization of the trans isomer because of unfavorable electronic and stericinteractions. Analysis of the results herein along with the structures of collagen-like peptides has led to atheory that links collagen stability to the interplay between the pyrrolidine ring pucker, and torsionalangles, and peptide bond trans/cis ratio of substituted proline residues.
3 ring position of the second proline residue stabilizes these triple helices.The aim of this study was to reveal the structural and energetic origins of this effect. The approach was toobtain experimental NMR data on model systems and to use these results to validate computational chemicalanalyses of these systems. The most striking effects of an electron-withdrawing substituent are on the ringpucker of the substituted proline (Proi) and on the trans/cis ratio of the Xaai-1-Proi peptide bond. NMRexperiments demonstrated that N-acetylproline methyl ester (AcProOMe) exists in both the C-endo andC-exo conformations (with the endo conformation slightly preferred), N-acetyl-4(R)-fluoroproline methylester (Ac-4R-FlpOMe) exists almost exclusively in the C-exo conformation, and N-acetyl-4(S)-fluoroprolinemethyl ester (Ac-4S-FlpOMe) exists almost exclusively in the C-endo conformation. In dioxane, the Ktrans/cisvalues for AcProOMe, Ac-4R-FlpOMe, and Ac-4S-FlpOMe are 3.0, 4.0, and 1.2, respectively. Densityfunctional theory (DFT) calculations with the (hybrid) B3LYP method were in good agreement with theexperimental data. Computational analysis with the natural bond orbital (NBO) paradigm shows that thepucker preference of the substituted prolyl ring is due to the gauche effect. The backbone torsional angles, and , were shown to correlate with ring pucker, which in turn correlates with the known and anglesin collagen-like peptides. The difference in Ktrans/cis between AcProOMe and Ac-4R-FlpOMe is due to an n * interaction associated with the Bürgi-Dunitz trajectory. The decrease in Ktrans/cis for Ac-4S-FlpOMecan be explained by destabilization of the trans isomer because of unfavorable electronic and stericinteractions. Analysis of the results herein along with the structures of collagen-like peptides has led to atheory that links collagen stability to the interplay between the pyrrolidine ring pucker, and torsionalangles, and peptide bond trans/cis ratio of substituted proline residues.