title: Effects of Cardiac Troponin I Mutation P83S on Contractile Properties and the Modulation by PKA-Mediated Phosphorylation.
abstract: cTnI(P82S) (cTnI(P83S) in rodents) resides at the I-T arm of cardiac troponin I (cTnI) and was initially identified as a disease-causing mutation of hypertrophic cardiomyopathy (HCM). However, later studies suggested this may not be true. We recently reported that introduction of an HCM-associated mutation in either inhibitory-peptide (cTnI(R146G)) or cardiac-specific N-terminus (cTnI(R21C)) of cTnI blunts the PKA-mediated modulation on myofibril activation/relaxation kinetics by prohibiting formation of intrasubunit contacts between these regions. Here, we tested whether this also occurs for cTnI(P83S). cTnI(P83S) increased both Ca(2+) binding affinity to cTn (KCa) and affinity of cTnC for cTnI (KC-I), and eliminated the reduction of KCa and KC-I observed for phosphorylated-cTnI(WT). In isolated myofibrils, cTnI(P83S) maintained maximal tension (TMAX) and Ca(2+) sensitivity of tension (pCa50). For cTnI(WT) myofibrils, PKA-mediated phosphorylation decreased pCa50 and sped up the slow-phase relaxation (especially for those Ca(2+) conditions that heart performs in vivo). Those effects were blunted for cTnI(P83S) myofibrils. Molecular-dynamics simulations suggested cTnI(P83S) moderately inhibited an intrasubunit interaction formation between inhibitory-peptide and N-terminus, but this "blunting" effect was weaker than that with cTnI(R146G) or cTnI(R21C). In summary, cTnI(P83S) has similar effects as other HCM-associated cTnI mutations on troponin and myofibril function even though it is in the I-T arm of cTnI.
authors.affiliation: Department of Bioengineering, University of Washington , Seattle, Washington 98105, United States.|National Biomedical Computation Resource, University of California San Diego , La Jolla, California 92093, United States.
authors.forename: Yuanhua
authors.initials: Y
authors.lastname: Cheng
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: Steffen
authors.initials: S
authors.lastname: Lindert
authors.affiliation: Department of Bioengineering, University of Washington , Seattle, Washington 98105, United States.
authors.forename: Lucas
authors.initials: L
authors.lastname: Oxenford
authors.affiliation: Department of Bioengineering, University of Washington , Seattle, Washington 98105, United States.
authors.forename: An-Yue
authors.initials: AY
authors.lastname: Tu
authors.affiliation: National Biomedical Computation Resource, University of California San Diego , La Jolla, California 92093, United States.|Department of Bioengineering, University of California San Diego , La Jolla, California 92093, United States.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: McCulloch
authors.affiliation: Department of Bioengineering, University of Washington , Seattle, Washington 98105, United States.|Center for Cardiovascular Biology, University of Washington , Seattle, Washington 98195, United States.
authors.forename: Michael
authors.initials: M
authors.lastname: Regnier
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008297:Male; D056004:Molecular Dynamics Simulation; D009154:Mutation; D009200:Myocardial Contraction / Q000502:physiology; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D009210:Myofibrils / Q000378:metabolism*; D010649:Phenylalanine / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D017207:Rats, Sprague-Dawley; D012694:Serine / Q000378:metabolism; D019210:Troponin I / Q000235:genetics / Q000378:metabolism*
chemical_list: D019210:Troponin I; D012694:Serine; D010649:Phenylalanine; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium