title: Interaction between troponin and myosin enhances contractile activity of myosin in cardiac muscle.
abstract: Ca(2+) signaling in striated muscle cells is critically dependent upon thin filament proteins tropomyosin (Tm) and troponin (Tn) to regulate mechanical output. Using in vitro measurements of contractility, we demonstrate that even in the absence of actin and Tm, human cardiac Tn (cTn) enhances heavy meromyosin MgATPase activity by up to 2.5-fold in solution. In addition, cTn without Tm significantly increases, or superactivates sliding speed of filamentous actin (F-actin) in skeletal motility assays by at least 12%, depending upon [cTn]. cTn alone enhances skeletal heavy meromyosin's MgATPase in a concentration-dependent manner and with sub-micromolar affinity. cTn-mediated increases in myosin ATPase may be the cause of superactivation of maximum Ca(2+)-activated regulated thin filament sliding speed in motility assays relative to unregulated skeletal F-actin. To specifically relate this classical superactivation to cardiac muscle, we demonstrate the same response using motility assays where only cardiac proteins were used, where regulated cardiac thin filament sliding speeds with cardiac myosin are >50% faster than unregulated cardiac F-actin. We additionally demonstrate that the COOH-terminal mobile domain of cTnI is not required for this interaction or functional enhancement of myosin activity. Our results provide strong evidence that the interaction between cTn and myosin is responsible for enhancement of cross-bridge kinetics when myosin binds in the vicinity of Tn on thin filaments. These data imply a novel and functionally significant molecular interaction that may provide new insights into Ca(2+) activation in cardiac muscle cells.
authors: Department of Biology, Barry University, Miami Shores, FL 33161, USA. bschoffstall@mail.barry.edu
authors: Brenda
authors: B
authors: Schoffstall
authors: Vincent A
authors: VA
authors: LaBarbera
authors: Nicolas M
authors: NM
authors: Brunet
authors: Belinda J
authors: BJ
authors: Gavino
authors: Lauren
authors: L
authors: Herring
authors: Sara
authors: S
authors: Heshmati
authors: Brittany H
authors: BH
authors: Kraft
authors: Vanessa
authors: V
authors: Inchausti
authors: Nancy L
authors: NL
authors: Meyer
authors: Danamarie
authors: D
authors: Moonoo
authors: Aya K
authors: AK
authors: Takeda
authors: Prescott Bryant
authors: PB
authors: Chase
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D020013:Calcium Signaling / Q000502:physiology*; D005453:Fluorescence; D006801:Humans; D009119:Muscle Contraction / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism* / Q000502:physiology; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism; D012044:Regression Analysis; D034421:Sus scrofa; D014336:Troponin / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; D014336:Troponin; D000251:Adenosine Triphosphatases; D009218:Myosins