Circular dichroism studies of distorted α-helices, twisted β-sheets, and β-turns
1988; Elsevier BV; Volume: 31; Issue: 1-2 Linguagem: Inglês
10.1016/0301-4622(88)80011-5
ISSN1873-4200
AutoresMark C. Manning, Mah Illangasekare, Robert W. Woody,
Tópico(s)Molecular spectroscopy and chirality
ResumoTheoretical models for calculating the circular dichroism (CD) of biopolymers have been constructed which allow the evaluation of the effects of geometric distortions within regular secondary structures. Outward tilting of the carbonyl group within α-helical structures yields calculated CD spectra with diminished intensity and a red-shifted maximum near 190 nm. The αII-helix provides an extreme example of this type of α-helix distortion. It is predicted that a mixture of α and αII structures in bacteriorhodopsin can account for its anomalous CD spectrum. The minimum length of α-helix required to produce an α-helix-like CD spectrum is calculated to be two to three turns (seven to eleven residues), while helices greater than 30 residues should provide adequate models of an infinite helix. Twisting of β-sheets is predicted to lead to an increase in CD intensity and significant shifts in band position. Calculated CD spectra for β-turn models are accurate for types II and II', but appear to be inadequate for type I turns.
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