期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：26
页码：E3337-E3344
DOI：10.1073/pnas.1506633112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceMyosin molecular motors generate forces in the cell and act as mechanosensors, adjusting their power outputs in response to mechanical loads. Little is known about the structural elements involved in myosin mechanosensing. Our results identify the N-terminal region (NTR) of the myosin-I protein as having an important role in tuning mechanochemistry. Appending the NTR from a highly tension-sensitive myosin (Myo1b) onto a less tension-sensitive motor (Myo1c) changes the identity of the primary force-sensitive transition of Myo1c, making it sensitive to forces <2 pN. Moreover, we show that the NTR stabilizes the post-power-stroke conformation. These results identify the NTR as an important structural element in myosin force sensing and suggest a mechanism for generating diversity of function among myosin isoforms. Myosins are molecular motors that generate force to power a wide array of motile cellular functions. Myosins have the inherent ability to change their ATPase kinetics and force-generating properties when they encounter mechanical loads; however, little is known about the structural elements in myosin responsible for force sensing. Recent structural and biophysical studies have shown that myosin-I isoforms, Myosin-Ib (Myo1b) and Myosin-Ic (Myo1c), have similar unloaded kinetics and sequences but substantially different responses to forces that resist their working strokes. Myo1b has the properties of a tension-sensing anchor, slowing its actin-detachment kinetics by two orders of magnitude with just 1 pN of resisting force, whereas Myo1c has the properties of a slow transporter, generating power without slowing under 1-pN loads that would stall Myo1b. To examine the structural elements that lead to differences in force sensing, we used single-molecule and ensemble kinetic techniques to show that the myosin-I N-terminal region (NTR) plays a critical role in tuning myosin-I mechanochemistry. We found that replacing the Myo1c NTR with the Myo1b NTR changes the identity of the primary force-sensitive transition of Myo1c, resulting in sensitivity to forces of <2 pN. Additionally, we found that the NTR plays an important role in stabilizing the post-power-stroke conformation. These results identify the NTR as an important structural element in myosin force sensing and suggest a mechanism for generating diversity of function among myosin isoforms.
