title: The role of caldesmon and its phosphorylation by ERK on the binding force of unphosphorylated myosin to actin.
abstract: BACKGROUND
  Studies conducted at the whole muscle level have shown that smooth muscle can maintain tension with low Adenosine triphosphate (ATP) consumption. Whereas it is generally accepted that this property (latch-state) is a consequence of the dephosphorylation of myosin during its attachment to actin, free dephosphorylated myosin can also bind to actin and contribute to force maintenance. We investigated the role of caldesmon (CaD) in regulating the binding force of unphosphorylated tonic smooth muscle myosin to actin.
  
  
  METHODS
  To measure the effect of CaD on the binding of unphosphorylated myosin to actin (in the presence of ATP), we used a single beam laser trap assay to quantify the average unbinding force (Funb) in the absence or presence of caldesmon, extracellular signal-regulated kinase (ERK)-phosphorylated CaD, or CaD plus tropomyosin.
  
  
  RESULTS
  Funb from unregulated actin (0.10±0.01pN) was significantly increased in the presence of CaD (0.17±0.02pN), tropomyosin (0.17±0.02pN) or both regulatory proteins (0.18±0.02pN). ERK phosphorylation of CaD significantly reduced the Funb (0.06±0.01pN). Inspection of the traces of the Funb as a function of time suggests that ERK phosphorylation of CaD decreases the binding force of myosin to actin or accelerates its detachment.
  
  
  CONCLUSIONS
  CaD enhances the binding force of unphosphorylated myosin to actin potentially contributing to the latch-state. ERK phosphorylation of CaD decreases this binding force to very low levels.
  
  
  CONCLUSIONS
  This study suggests a mechanism that likely contributes to the latch-state and that explains the muscle relaxation from the latch-state.
authors.affiliation: Meakins-Christie Laboratories, McGill University, Montréal, Québec, Canada; Department of Biomedical Engineering, McGill University, Montréal, Québec, Canada.
authors.forename: Horia Nicolae
authors.initials: HN
authors.lastname: Roman
authors.affiliation: Meakins-Christie Laboratories, McGill University, Montréal, Québec, Canada.
authors.forename: Nedjma B
authors.initials: NB
authors.lastname: Zitouni
authors.affiliation: Meakins-Christie Laboratories, McGill University, Montréal, Québec, Canada.
authors.forename: Linda
authors.initials: L
authors.lastname: Kachmar
authors.affiliation: Department of Medicine, McGill University, Montréal, Québec, Canada; Department of Epidemiology, Biostatistics & Occupational Health, McGill University, Montréal, Québec, Canada; Respiratory Epidemiology & Clinical Research Unit, Montreal Chest Institute, Montréal, Québec, Canada.
authors.forename: Andrea
authors.initials: A
authors.lastname: Benedetti
authors.affiliation: Institute for Biomedical Aging Research, Smooth Muscle Lab at the Life Science Center, Austrian Academy of Sciences, Mitterweg 24, A-6020 Innsbruck, Austria.
authors.forename: Apolinary
authors.initials: A
authors.lastname: Sobieszek
authors.affiliation: Meakins-Christie Laboratories, McGill University, Montréal, Québec, Canada; Department of Medicine, McGill University, Montréal, Québec, Canada; Department of Biomedical Engineering, McGill University, Montréal, Québec, Canada; Department of Physiology, McGill University, Montréal, Québec, Canada. Electronic address: anne-marie.lauzon@mcgill.ca.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Lauzon
keywords: Caldesmon; In vitro motility assay laser trap; Latch-state; Myosin; Phosphorylation; Tropomyosin
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