Manning M C, Illangasekare M, Woody R W
Department of Biochemistry, Colorado State University, Fort Collins 80523.
Biophys Chem. 1988 Aug;31(1-2):77-86. doi: 10.1016/0301-4622(88)80011-5.
Theoretical 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 alpha-helical structures yields calculated CD spectra with diminished intensity and a red-shifted maximum near 190 nm. The alpha II-helix provides an extreme example of this type of alpha-helix distortion. It is predicted that a mixture of alpha and alpha II structures in bacteriorhodopsin can account for its anomalous CD spectrum. The minimum length of alpha-helix required to produce an alpha-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 beta-sheets is predicted to lead to an increase in CD intensity and significant shifts in band position. Calculated CD spectra for beta-turn models are accurate for types II and II', but appear to be inadequate for type I turns.
已构建用于计算生物聚合物圆二色性（CD）的理论模型，这些模型可用于评估规则二级结构内几何畸变的影响。α-螺旋结构中羰基的向外倾斜会产生计算得到的CD光谱，其强度减弱且在190nm附近有一个红移的最大值。αII-螺旋是这种α-螺旋畸变类型的一个极端例子。据预测，细菌视紫红质中α和αII结构的混合物可以解释其异常的CD光谱。产生类似α-螺旋CD光谱所需的α-螺旋最小长度经计算为两到三圈（七到十一个残基），而大于30个残基的螺旋应能提供足够的无限螺旋模型。β-折叠的扭曲预计会导致CD强度增加和谱带位置的显著移动。β-转角模型的计算CD光谱对于II型和II'型是准确的，但对于I型转角似乎并不适用。
