title: Chemical decoupling of ATPase activation and force production from the contractile cycle in myosin by steric hindrance of lever-arm movement.
abstract: The myosin motor protein generates force in muscle by hydrolyzing Adenosine 5'-triphosphate (ATP) while interacting transiently with actin. Structural evidence suggests the myosin globular head (subfragment 1 or S1) is articulated with semi-rigid catalytic and lever-arm domains joined by a flexible converter domain. According to the prevailing hypothesis for energy transduction, ATP binding and hydrolysis in the catalytic domain drives the relative movement of the lever arm. Actin binding and reversal of the lever-arm movement (power stroke) applies force to actin. These domains interface at the reactive lysine, Lys84, where trinitrophenylation (TNP-Lys84-S1) was observed in this work to block actin activation of myosin ATPase and in vitro sliding of actin over myosin. TNP-Lys84-S1's properties and interactions with actin were examined to determine how trinitrophenylation causes these effects. Weak and strong actin binding, the rate of mantADP release from actomyosin, and actomyosin dissociation by ATP were equivalent in TNP-Lys84-S1 and native S1. Molecular dynamics calculations indicate that lever-arm movement inhibition during ATP hydrolysis and the power stroke is caused by steric clashes between TNP and the converter or lever-arm domains. Together these findings suggest that TNP uncouples actin activation of myosin ATPase and the power stroke from other steps in the contraction cycle by inhibiting the converter and lever-arm domain movements.
authors.affiliation: Department of Oral Biology, Hebrew University Hadassah School of Dental Medicine, Jerusalem, Israel 91120.
authors.forename: Andras
authors.initials: A
authors.lastname: Muhlrad
authors.forename: Y Michael
authors.initials: YM
authors.lastname: Peyser
authors.forename: Mahta
authors.initials: M
authors.lastname: Nili
authors.forename: Katalin
authors.initials: K
authors.lastname: Ajtai
authors.forename: Emil
authors.initials: E
authors.lastname: Reisler
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Burghardt
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000502:physiology; D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000502:physiology; D000818:Animals; D002645:Chickens; D003198:Computer Simulation; D004735:Energy Transfer; D006868:Hydrolysis; D046911:Macromolecular Substances; D008958:Models, Molecular; D020409:Molecular Motor Proteins / Q000737:chemistry* / Q000502:physiology; D009038:Motion; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000502:physiology; D015879:Myosin Subfragments / Q000737:chemistry / Q000502:physiology; D009218:Myosins / Q000737:chemistry* / Q000502:physiology; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011817:Rabbits; D013237:Stereoisomerism; D013314:Stress, Mechanical; D014301:Trinitrobenzenes / Q000737:chemistry
chemical_list: D000199:Actins; D046911:Macromolecular Substances; D020409:Molecular Motor Proteins; D015879:Myosin Subfragments; D014301:Trinitrobenzenes; D000251:Adenosine Triphosphatases; D009218:Myosins