Chavali Sai Shashank, Carman Peter J, Shuman Henry, Ostap E Michael, Sindelar Charles V
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8103.
Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.
Proc Natl Acad Sci U S A. 2025 Mar 4;122(9):e2415457122. doi: 10.1073/pnas.2415457122. Epub 2025 Feb 27.
Myosin-IC (myo1c) is a class-I myosin that supports transport and remodeling of the plasma membrane and membrane-bound vesicles. Like other members of the myosin family, its biochemical kinetics are altered in response to changes in mechanical loads that resist the power stroke. However, myo1c is unique in that the primary force-sensitive kinetic transition is the isomerization that follows ATP binding, not ADP release as in other slow myosins. Myo1c also powers actin gliding along curved paths, propelling actin filaments in leftward circles. To understand the origins of this unique force-sensing and motile behavior, we solved actin-bound myo1c cryo-EM structures in the presence and absence of ADP. Our structures reveal that in contrast with other myosins, the myo1c lever arm swing is skewed, partly due to a different actin interface that reorients the motor domain on actin. The structures also reveal unique nucleotide-dependent behavior of both the nucleotide pocket as well as an element called the N-terminal extension (NTE). We incorporate these observations into a model that explains why force primarily regulates ATP binding in myo1c, rather than ADP release as in other myosins. Integrating our cryo-EM data with available crystallography structures allows the modeling of full-length myo1c during force generation, supplying insights into its role in membrane remodeling. These results highlight how relatively minor sequence differences in members of the myosin superfamily can significantly alter power stroke geometry and force-sensing properties, with important implications for biological function.
肌球蛋白-IC（myo1c）是一种I类肌球蛋白，支持质膜和膜结合囊泡的运输与重塑。与肌球蛋白家族的其他成员一样，其生化动力学响应抵抗动力冲程的机械负荷变化而改变。然而，myo1c的独特之处在于，主要的力敏感动力学转变是ATP结合后的异构化，而不是像其他慢速肌球蛋白那样是ADP释放。Myo1c还能驱动肌动蛋白沿弯曲路径滑动，使肌动蛋白丝向左旋转。为了理解这种独特的力感知和运动行为的起源，我们解析了在有和没有ADP存在的情况下与肌动蛋白结合的myo1c冷冻电镜结构。我们的结构表明，与其他肌球蛋白不同，myo1c的杠杆臂摆动是倾斜的，部分原因是肌动蛋白界面不同，它会使肌动蛋白上的运动结构域重新定向。这些结构还揭示了核苷酸口袋以及一个称为N端延伸（NTE）的元件独特的核苷酸依赖性行为。我们将这些观察结果纳入一个模型，该模型解释了为什么力主要调节myo1c中的ATP结合，而不是像其他肌球蛋白那样调节ADP释放。将我们的冷冻电镜数据与现有的晶体学结构相结合，可以对力产生过程中的全长myo1c进行建模，从而深入了解其在膜重塑中的作用。这些结果突出了肌球蛋白超家族成员中相对较小的序列差异如何能显著改变动力冲程几何结构和力感知特性，对生物学功能具有重要意义。
