Chin Der-Hang, Woody Robert W, Rohl Carol A, Baldwin Robert L
Department of Biochemistry, Beckman Center, Stanford University Medical Center, CA 94305, USA.
Proc Natl Acad Sci U S A. 2002 Nov 26;99(24):15416-21. doi: 10.1073/pnas.232591399. Epub 2002 Nov 11.
Very short alanine peptide helices can be studied in a fixed-nucleus, helix-forming system [Siedlicka, M., Goch, G., Ejchart, A., Sticht, H. & Bierzynski, A. (1999) Proc. Natl. Acad. Sci. USA 96, 903-908]. In a 12-residue sequence taken from an EF-hand protein, the four C-terminal peptide units become helical when the peptide binds La(3+), and somewhat longer helices may be made by adding alanine residues at the C terminus. The helices studied here contain 4, 8, or 11 peptide units. Surprisingly, these short fixed-nucleus helices remain almost fully helical from 4 to 65 degrees C, according to circular dichroism results reported here, and in agreement with titration calorimetry results reported recently. These peptides are used here to define the circular dichroism properties of short helices, which are needed for accurate measurement of helix propensities. Two striking properties are: (i) the temperature coefficient of mean peptide ellipticity depends strongly on helix length; and (ii) the intensity of the signal decreases much less rapidly with helix length, for very short helices, than supposed in the past. The circular dichroism spectra of the short helices are compared with new theoretical calculations, based on the experimentally determined direction of the NV(1) transition moment.
极短的丙氨酸肽螺旋可以在一个固定核的螺旋形成系统中进行研究[Siedlicka, M., Goch, G., Ejchart, A., Sticht, H. & Bierzynski, A. (1999) Proc. Natl. Acad. Sci. USA 96, 903 - 908]。在一个取自EF手蛋白的12个残基序列中，当该肽与La(3+)结合时，四个C末端肽单元会形成螺旋，并且通过在C末端添加丙氨酸残基可以形成更长一些的螺旋。这里研究的螺旋包含4、8或11个肽单元。令人惊讶的是，根据此处报道的圆二色性结果以及与最近报道的滴定热分析结果一致，这些短的固定核螺旋在4至65摄氏度范围内几乎保持完全螺旋状态。这里使用这些肽来定义短螺旋的圆二色性特性，这对于准确测量螺旋倾向是必需的。两个显著特性是：(i)平均肽椭圆率的温度系数强烈依赖于螺旋长度；(ii)对于极短的螺旋，信号强度随螺旋长度的下降速度比过去认为得要慢得多。基于实验确定的NV(1)跃迁矩方向，将短螺旋的圆二色性光谱与新的理论计算进行了比较。
