title: Skeletal muscle resists stretch by rapid binding of the second motor domain of myosin to actin.
abstract: A shortening muscle is a machine that converts metabolic energy into mechanical work, but, when a muscle is stretched, it acts as a brake, generating a high resistive force at low metabolic cost. The braking action of muscle can be activated with remarkable speed, as when the leg extensor muscles rapidly decelerate the body at the end of a jump. Here we used time-resolved x-ray and mechanical measurements on isolated muscle cells to elucidate the molecular basis of muscle braking and its rapid control. We show that a stretch of only 5 nm between each overlapping set of myosin and actin filaments in a muscle sarcomere is sufficient to double the number of myosin motors attached to actin within a few milliseconds. Each myosin molecule has two motor domains, only one of which is attached to actin during shortening or activation at constant length. A stretch strains the attached motor domain, and we propose that combined steric and mechanical coupling between the two domains promotes attachment of the second motor domain. This mechanism allows skeletal muscle to resist external stretch without increasing the force per motor and provides an answer to the longstanding question of the functional role of the dimeric structure of muscle myosin.
authors: Laboratorio di Fisiologia, Dipartimento di Biologia Animale e Genetica, Università degli Studi di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Italy.
authors: Elisabetta
authors: E
authors: Brunello
authors: Massimo
authors: M
authors: Reconditi
authors: Ravikrishnan
authors: R
authors: Elangovan
authors: Marco
authors: M
authors: Linari
authors: Yin-Biao
authors: YB
authors: Sun
authors: Theyencheri
authors: T
authors: Narayanan
authors: Pierre
authors: P
authors: Panine
authors: Gabriella
authors: G
authors: Piazzesi
authors: Malcolm
authors: M
authors: Irving
authors: Vincenzo
authors: V
authors: Lombardi
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D052580:Muscle Stretching Exercises; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D009218:Myosins / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary; D011896:Rana temporaria
chemical_list: D000199:Actins; D009218:Myosins