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. 1977 Aug;74(8):3208–3212. doi: 10.1073/pnas.74.8.3208

Identification of β,β-turns and unordered conformations in polypeptide chains by vacuum ultraviolet circular dichroism

S Brahms *, J Brahms *, G Spach †, A Brack †
PMCID: PMC431499  PMID: 269385

Abstract

Different conformations of polypeptides were characterized by measurements of the circular dichroism (CD) extended into the vacuum ultraviolet region. (i) The linear β-pleated sheet structure was characterized in a broad ultraviolet region down to 165 nm by examination of copolypeptides composed of alternating hydrophobic and hydrophilic amino-acid residues, e.g., poly(Lys-Leu-Lys-Leu). A short-wavelength intense band was found at about 169 nm, which is characteristic of β-pleated sheet conformation. (ii) The β-turns were experimentally measured using poly(Ala2-Gly2) in a broad spectral region down to 165 nm with accuracy. The observed CD spectrum is in excellent qualitative agreement with the theoretical curve calculated by Woody for the β-turns of type II and/or I of Venkatachalam. The similarity in shape between the theoretical curve and the observed CD spectra suggests a dominance of β-turn segments in the poly(Ala2-Gly2) structure. The presence of β-turns in poly(Ala2-Gly2) is also in agreement with the characterization of this polypeptide by solid state methods (electron microscopy and x-ray diffraction). The CD spectrum of β-turns is characterized by a very intense band at 207.5 nm and strong negative bands at 191 and 169 nm. Copolypeptides such as poly(Ala2-Gly3) and poly(Ala3-Gly3) yielded a similar type of CD spectrum, analysis of which indicates that a large fraction of their residues is contained in β-turn regions. (iii) The CD spectrum of the unordered chain of these alternating copolypeptides in salt-free solution is observed in the vacuum ultraviolet region.

Keywords: polypeptide conformation, β-pleated sheets, reverse turns, protein structure

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Selected References

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