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Local structure due to an aromatic-amide interaction observed by 1H-nuclear magnetic resonance spectroscopy in peptides related to the N terminus of bovine pancreatic trypsin inhibitor.

A synthetic peptide corresponding to the 15 N-terminal residues of bovine pancreatic trypsin inhibitor, with serine replacing the two cysteine residues, has been characterized by 1H-nuclear magnetic resonance spectroscopy. This peptide has a very disordered conformation that is essentially the same when it is part of the analogue of the (30-51) one-disulphide intermediate in folding. This confirms the conclusion of a previous paper, that the (30-51) intermediate is partially folded, with the N-terminal segment disordered. Local elements of non-random conformation were observed in the peptide. Especially prominent was an apparently electrostatic interaction between the face of the aromatic ring of Tyr10 and the amide group of Gly12, which caused the latter to have a very anomalous chemical shift. A similar interaction was observed in shorter peptides, especially in tetrapeptides with the sequences Tyr/Phe-X-Gly-Y. The local nature of this interaction indicates that it should be a general feature in peptides and in unfolded proteins with such a sequence.