Department of Biochemistry, Stanford University, Stanford, California, USA.
Biophys J. 2009 Dec 2;97(11):2993-9. doi: 10.1016/j.bpj.2009.09.009.
A relatively unknown protein structure motif forms stable isolated single alpha-helices, termed ER/K alpha-helices, in a wide variety of proteins and has been shown to be essential for the function of some molecular motors. The flexibility of the ER/K alpha-helix determines whether it behaves as a force transducer, rigid spacer, or flexible linker in proteins. In this study, we quantify this flexibility in terms of persistence length, namely the length scale over which it is rigid. We use single-molecule optical trapping and small-angle x-ray scattering, combined with Monte Carlo simulations to demonstrate that the Kelch ER/K alpha-helix behaves as a wormlike chain with a persistence length of approximately 15 nm or approximately 28 turns of alpha-helix. The ER/K alpha-helix length in proteins varies from 3 to 60 nm, with a median length of approximately 5 nm. Knowledge of its persistence length enables us to define its function as a rigid spacer in a translation initiation factor, as a force transducer in the mechanoenzyme myosin VI, and as a flexible spacer in the Kelch-motif-containing protein.
一种相对未知的蛋白质结构基序形成稳定的孤立的单一α-螺旋，称为 ER/Kα-螺旋，在各种蛋白质中都有存在，并已被证明对一些分子马达的功能至关重要。ER/Kα-螺旋的灵活性决定了它在蛋白质中是作为力传感器、刚性间隔物还是柔性连接物发挥作用。在这项研究中，我们根据持久长度（即其刚性的尺度）来量化这种灵活性。我们使用单分子光学捕获和小角度 X 射线散射，并结合蒙特卡罗模拟，证明 Kelch ER/Kα-螺旋表现为具有约 15nm 或约 28 圈α-螺旋的蠕虫链。蛋白质中的 ER/Kα-螺旋长度从 3nm 到 60nm 不等，中位数约为 5nm。了解其持久长度使我们能够将其功能定义为起始因子中的刚性间隔物、机械酶肌球蛋白 VI 中的力传感器以及 Kelch 基序蛋白中的柔性间隔物。
