NMR‐Structural Investigations of a β3‐Dodecapeptide with Proteinogenic Side Chains in Methanol and in Aqueous Solutions |
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Authors: | Touraj Etezady‐Esfarjani,Christian Hilty,Kurt Wü thrich,Magnus Rueping,Jü rg Schreiber,Dieter Seebach |
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Abstract: | The structural properties of an all‐β3‐dodecapeptide with the sequence H‐β‐HLys(Nε‐CO(CH2)3‐S Acm)‐β‐HPhe‐β‐HTyr‐β‐HLeu‐β‐HLys‐β‐HSer‐β‐HLys‐β‐HPhe‐β‐HSer‐β‐HVal‐β‐HLys‐β‐HAla‐OH ( 1 ) have been studied by two‐dimensional homonuclear 1H‐NMR and by CD spectroscopy. In MeOH solution, high‐resolution NMR spectroscopy showed that the β‐dodecapeptide forms an (M)‐314‐helix, and the CD spectrum corresponds to the pattern expected for an (M)‐314‐helical secondary structure. In aqueous solution, however, the peptide adopts a predominantly extended conformation without regular secondary‐structure elements, which is in agreement with the absence of the characteristic trough near 215 nm in the CD spectrum. The NMR and CD measurements with solutions of 1 in MeOH containing 3M urea further indicated that the peptide retains the regular secondary structural elements under these conditions, whereas, after addition of 40% (v/v) H2O to the MeOH solution, the large 1H‐chemical‐shift dispersion indicative of a defined spatial peptide fold was lost. The β3‐dodecapeptide is – so far – the longest β‐peptide shown to adopt a regular (M)‐314‐helix conformation in an organic solvent. The observation that the structure of this long β3‐peptide is not maintained in aqueous solution indicates that the (M)‐314‐fold is primarily stabilized by short‐range interactions. |
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