title: Mechanochemical tuning of myosin-I by the N-terminal region.
abstract: 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.
authors.affiliation: Pennsylvania Muscle Institute and the Department of Physiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Greenberg
authors.affiliation: Pennsylvania Muscle Institute and the Department of Physiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Tianming
authors.initials: T
authors.lastname: Lin
authors.affiliation: Pennsylvania Muscle Institute and the Department of Physiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Henry
authors.initials: H
authors.lastname: Shuman
authors.affiliation: Pennsylvania Muscle Institute and the Department of Physiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104 ostap@mail.med.upenn.edu.
authors.forename: E Michael
authors.initials: EM
authors.lastname: Ostap
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D008958:Models, Molecular; D008969:Molecular Sequence Data; D024461:Myosin Type I / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D018411:Spodoptera
chemical_list: D024461:Myosin Type I
keywords: mechanochemistry; mechanosensing; optical tweezers; single molecule; transient kinetics