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J Am Chem Soc. 2005 Jul 13;127(27):9700-1.

Single peptide bonds exhibit poly(pro)II ("random coil") circular dichroism spectra.

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Institute of Cell and Molecular Biosciences, University of Newcastle-upon-Tyne, Framlington Place, Newcastle-upon-Tyne NE2 4HH, UK.


The far-UV circular dichroism spectra of a series of amino acid derivatives containing single peptide bonds have been measured. The N-acetyl-alanine displays a polyproline (PP) II-like spectrum, but alaninamide shows a very weak positive signal. Similarly Gly-Ala shows a PPII spectrum, but Ala-Gly does not. On heating, the spectrum shows a two-state transition also shown by long PPII polypeptides. Thus the characteristic PPII negative maximum at <200 nm results from the coupling of a peptide bond N-terminal to the chiral alpha-carbon, and therefore the simplest peptide bonds have a preferred conformation that defines the spectrum of disordered proteins of any size.

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