title: Tropomyosin Ser-283 pseudo-phosphorylation slows myofibril relaxation.
abstract: Tropomyosin (Tm) is a central protein in the Ca(2+) regulation of striated muscle. The αTm isoform undergoes phosphorylation at serine residue 283. While the biochemical and steady-state muscle function of muscle purified Tm phosphorylation have been explored, the effects of Tm phosphorylation on the dynamic properties of muscle contraction and relaxation are unknown. To investigate the kinetic regulatory role of αTm phosphorylation we expressed and purified native N-terminal acetylated Ser-283 wild-type, S283A phosphorylation null and S283D pseudo-phosphorylation Tm mutants in insect cells. Purified Tm's regulate thin filaments similar to that reported for muscle purified Tm. Steady-state Ca(2+) binding to troponin C (TnC) in reconstituted thin filaments did not differ between the 3 Tm's, however disassociation of Ca(2+) from filaments containing pseudo-phosphorylated Tm was slowed compared to wild-type Tm. Replacement of pseudo-phosphorylated Tm into myofibrils similarly prolonged the slow phase of relaxation and decreased the rate of the fast phase without altering activation kinetics. These data demonstrate that Tm pseudo-phosphorylation slows deactivation of the thin filament and muscle force relaxation dynamics in the absence of dynamic and steady-state effects on muscle activation. This supports a role for Tm as a key protein in the regulation of muscle relaxation dynamics.
authors.affiliation: Department of Physiology and Cell Biology and The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, United States.
authors.forename: Benjamin R
authors.initials: BR
authors.lastname: Nixon
authors.forename: Bin
authors.initials: B
authors.lastname: Liu
authors.forename: Beatrice
authors.initials: B
authors.lastname: Scellini
authors.forename: Chiara
authors.initials: C
authors.lastname: Tesi
authors.forename: Nicoletta
authors.initials: N
authors.lastname: Piroddi
authors.forename: Ozgur
authors.initials: O
authors.lastname: Ogut
authors.forename: R John
authors.initials: RJ
authors.lastname: Solaro
authors.forename: Mark T
authors.initials: MT
authors.lastname: Ziolo
authors.forename: Paul M L
authors.initials: PM
authors.lastname: Janssen
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Davis
authors.forename: Corrado
authors.initials: C
authors.lastname: Poggesi
authors.forename: Brandon J
authors.initials: BJ
authors.lastname: Biesiadecki
mesh_terms: D000107:Acetylation; D008841:Actin Cytoskeleton / Q000378:metabolism / Q000502:physiology; D000818:Animals; D016367:Baculoviridae / Q000235:genetics / Q000378:metabolism; D001696:Biomechanical Phenomena; D002118:Calcium / Q000378:metabolism; D003001:Cloning, Molecular; D004789:Enzyme Activation; D051379:Mice; D009126:Muscle Relaxation; D054792:Muscle, Striated / Q000166:cytology / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009210:Myofibrils / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015879:Myosin Subfragments / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011817:Rabbits; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism*; D061987:Sf9 Cells; D014335:Tropomyosin / Q000235:genetics / Q000378:metabolism*
chemical_list: D015879:Myosin Subfragments; D011994:Recombinant Proteins; C490774:Tpm1 protein, mouse; D014335:Tropomyosin; D012694:Serine; D002118:Calcium