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À propos de : Retention of the Cis Proline Conformation in Tripeptide Fragments ofBovine Pancreatic Ribonuclease A Containing a Non-natural ProlineAnalogue, 5,5-Dimethylproline        

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  • Retention of the Cis Proline Conformation in Tripeptide Fragments ofBovine Pancreatic Ribonuclease A Containing a Non-natural ProlineAnalogue, 5,5-Dimethylproline
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Abstract
  • Attention is focused on l-5,5-dimethylproline (dmP) as a substitute to lock l-proline (Pro) in a cisconformation in peptides and proteins, to prevent cis/trans isomerization when a protein with cis X-Pro peptidegroups unfolds. Procedures have been developed to obtain optically pure l-dmP and to incorporate this stericallyhindered residue as the central one in tripeptides that are suitable for fragment coupling to prepare syntheticproteins. Based on the sequences of residues 92−94 (Tyr-Pro-Asn:YPN) and 113−115 (Asn-Pro-Tyr: NPY)in bovine pancreatic ribonuclease A (RNase A), in which the X-Pro peptide groups are in the cis conformation,the tripeptides Ac-Tyr-dmP-Asn (YdmPN) and Ac-Asn-dmP-Tyr (NdmPY) were synthesized, and their structureswere determined by 2D 1H nuclear magnetic resonance (NMR) spectroscopy. YdmPN was found to existsolely in the cis conformation between 6 and 60 °C, whereas NdmPY was found to have some trans componentthat increased from about 10% to about 21% as the temperature increased over the range between 6 and 80°C. Both YdmPN and cis-NdmPY adopt a type VI reverse turn, as does proline. The NMR structures ofYdmPN and cis-NdmPY are comparable with the X-ray structures of the corresponding portions of RNase A,and the NMR structure of trans-NdmPY is compatible with the X-ray structure of the isolated tripeptide,Ac-NPY. These results demonstrate that l-dmP is a promising substitute for proline in a variety of proteinproblems to constrain the X-Pro peptide group to the cis conformation.
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