Liao Jung-Chi, Elting Mary Williard, Delp Scott L, Spudich James A, Bryant Zev
Department of Bioengineering, Stanford University, Stanford, CA 94305, USA.
J Mol Biol. 2009 Oct 2;392(4):862-7. doi: 10.1016/j.jmb.2009.07.046. Epub 2009 Jul 22.
Myosins have diverse mechanical properties reflecting a range of cellular roles. A major challenge is to understand the structural basis for generating novel functions from a common motor core. Myosin VI (M6) is specialized for processive motion toward the (-) end of actin filaments. We have used engineered M6 motors to test and refine the "redirected power stroke" model for (-) end directionality and to explore poorly understood structural requirements for processive stepping. Guided by crystal structures and molecular modeling, we fused artificial lever arms to the catalytic head of M6 at several positions, retaining varying amounts of native structure. We found that an 18-residue alpha-helical insert is sufficient to reverse the directionality of the motor, with no requirement for any calmodulin light chains. Further, we observed robust processive stepping of motors with artificial lever arms, demonstrating that processivity can arise without optimizing lever arm composition or mechanics.
肌球蛋白具有多样的力学特性，反映了一系列细胞功能。一个主要挑战是理解从共同的马达核心产生新功能的结构基础。肌球蛋白VI（M6）专门用于向肌动蛋白丝的（-）端进行持续性运动。我们使用工程化的M6马达来测试和完善用于（-）端方向性的“重定向动力冲程”模型，并探索对持续性步进理解不足的结构要求。在晶体结构和分子建模的指导下，我们在几个位置将人工杠杆臂融合到M6的催化头部，保留了不同数量的天然结构。我们发现一个18个残基的α螺旋插入物足以逆转马达的方向性，而不需要任何钙调蛋白轻链。此外，我们观察到带有人工杠杆臂的马达有强大的持续性步进，表明持续性可以在不优化杠杆臂组成或力学的情况下产生。
