Lakkaraju Sirish Kaushik, Hwang Wonmuk
Department of Biomedical Engineering, Texas A&M University, College Station TX 77843 Tel.: +1-979-458-0178, ,
Cell Mol Bioeng. 2009 Mar 1;2(1):57-65. doi: 10.1007/s12195-009-0050-1.
Alpha-helical coiled-coils are common protein structural motifs. Whereas vast information is available regarding their structure, folding, and stability, far less is known about their elastic properties, even though they play mechanical roles in many cases such as tropomyosin in muscle contraction or neck stalks of kinesin or myosin motor proteins. Using computer simulations, we characterized elastic properties of coiled-coils, either globally or locally. Global bending stiffness of standard leucine zipper coiled-coils was calculated using normal mode analysis. Mutations in hydrophobic residues involved in the knob-into-hole interface between the two alpha-helices affect elasticity significantly, whereas charged side chains forming inter-helical salt bridges do not. This suggests that coiled-coils with less regular heptad periodicity may have regional variations in flexibility. We show this by the flexibility map of tropomyosin, which was constructed by a local fluctuation analysis. Overall, flexibility varies by more than twofold and increases towards the C-terminal region of the molecule. Describing the coiled-coil as a twisted tape, it is generally more flexible in the splay bending than in the bending of the broad face. Actin binding sites in alpha zones show local rigidity minima. Broken core regions due to acidic residues at the hydrophobic face such as the Asp137 and the Glu218 are found to be the most labile with moduli for splay and broad face bending as 70 nm and 116 nm respectively. Such variation in flexibility could be relevant to the tropomyosin function, especially for moving across the non-uniform surface of F-actin to regulate myosin binding.
α-螺旋卷曲螺旋是常见的蛋白质结构基序。尽管关于它们的结构、折叠和稳定性已有大量信息，但对于它们的弹性特性却知之甚少，尽管它们在许多情况下发挥着机械作用，如肌肉收缩中的原肌球蛋白或驱动蛋白或肌球蛋白运动蛋白的颈部柄。通过计算机模拟，我们对卷曲螺旋的弹性特性进行了全局或局部表征。使用正常模式分析计算了标准亮氨酸拉链卷曲螺旋的全局弯曲刚度。参与两个α-螺旋之间旋钮-入-孔界面的疏水残基突变会显著影响弹性，而形成螺旋间盐桥的带电侧链则不会。这表明七肽周期性不太规则的卷曲螺旋可能在柔韧性上存在区域差异。我们通过原肌球蛋白的柔韧性图谱展示了这一点，该图谱是通过局部波动分析构建的。总体而言，柔韧性变化超过两倍，并向分子的C端区域增加。将卷曲螺旋描述为扭曲的带子，它通常在展开弯曲中比在宽面弯曲中更灵活。α区的肌动蛋白结合位点显示出局部刚性最小值。由于疏水面上的酸性残基（如Asp137和Glu218）导致的核心区域断裂被发现是最不稳定的，展开和宽面弯曲的模量分别为70纳米和116纳米。这种柔韧性的变化可能与原肌球蛋白的功能相关，特别是在跨F-肌动蛋白的不均匀表面移动以调节肌球蛋白结合方面。
