title: Cardiac myosin binding protein C phosphorylation affects cross-bridge cycle's elementary steps in a site-specific manner.
abstract: Based on our recent finding that cardiac myosin binding protein C (cMyBP-C) phosphorylation affects muscle contractility in a site-specific manner, we further studied the force per cross-bridge and the kinetic constants of the elementary steps in the six-state cross-bridge model in cMyBP-C mutated transgenic mice for better understanding of the influence of cMyBP-C phosphorylation on contractile functions. Papillary muscle fibres were dissected from cMyBP-C mutated mice of ADA (Ala273-Asp282-Ala302), DAD (Asp273-Ala282-Asp302), SAS (Ser273-Ala282-Ser302), and t/t (cMyBP-C null) genotypes, and the results were compared to transgenic mice expressing wide-type (WT) cMyBP-C. Sinusoidal analyses were performed with serial concentrations of ATP, phosphate (Pi), and ADP. Both t/t and DAD mutants significantly reduced active tension, force per cross-bridge, apparent rate constant (2πc), and the rate constant of cross-bridge detachment. In contrast to the weakened ATP binding and enhanced Pi and ADP release steps in t/t mice, DAD mice showed a decreased ADP release without affecting the ATP binding and the Pi release. ADA showed decreased ADP release, and slightly increased ATP binding and cross-bridge detachment steps, whereas SAS diminished the ATP binding step and accelerated the ADP release step. t/t has the broadest effects with changes in most elementary steps of the cross-bridge cycle, DAD mimics t/t to a large extent, and ADA and SAS predominantly affect the nucleotide binding steps. We conclude that the reduced tension production in DAD and t/t is the result of reduced force per cross-bridge, instead of the less number of strongly attached cross-bridges. We further conclude that cMyBP-C is an allosteric activator of myosin to increase cross-bridge force, and its phosphorylation status modulates the force, which is regulated by variety of protein kinases.
authors.affiliation: Department of Anatomy and Cell Biology, College of Medicine, University of Iowa, Iowa City, Iowa, United States of America; School of Nursing, Soochow University, Suzhou, Jiangsu, China.
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois, United States of America.
authors.forename: Sakthivel
authors.initials: S
authors.lastname: Sadayappan
authors.affiliation: Department of Anatomy and Cell Biology, College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Masakata
authors.initials: M
authors.lastname: Kawai
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000465:Algorithms; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D005838:Genotype; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles / Q000378:metabolism; D007700:Kinetics; D008822:Mice, Transgenic; D009119:Muscle Contraction / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D010210:Papillary Muscles / Q000378:metabolism / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism / Q000494:pharmacology; D010766:Phosphorylation; D000099163:Myosin Binding Protein C
chemical_list: D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D002352:Carrier Proteins; D010710:Phosphates; D000099163:Myosin Binding Protein C