title: Computational studies of the effect of the S23D/S24D troponin I mutation on cardiac troponin structural dynamics.
abstract: During β-adrenergic stimulation, cardiac troponin I (cTnI) is phosphorylated by protein kinase A (PKA) at sites S23/S24, located at the N-terminus of cTnI. This phosphorylation has been shown to decrease KCa and pCa50, and weaken the cTnC-cTnI (C-I) interaction. We recently reported that phosphorylation results in an increase in the rate of early, slow phase of relaxation (kREL,slow) and a decrease in its duration (tREL,slow), which speeds up the overall relaxation. However, as the N-terminus of cTnI (residues 1-40) has not been resolved in the whole cardiac troponin (cTn) structure, little is known about the molecular-level behavior within the whole cTn complex upon phosphorylation of the S23/S24 residues of cTnI that results in these changes in function. In this study, we built up the cTn complex structure (including residues cTnC 1-161, cTnI 1-172, and cTnT 236-285) with the N-terminus of cTnI. We performed molecular-dynamics (MD) simulations to elucidate the structural basis of PKA phosphorylation-induced changes in cTn structure and Ca(2+) binding. We found that introducing two phosphomimic mutations into sites S23/S24 had no significant effect on the coordinating residues of Ca(2+) binding site II. However, the overall fluctuation of cTn was increased and the C-I interaction was altered relative to the wild-type model. The most significant changes involved interactions with the N-terminus of cTnI. Interestingly, the phosphomimic mutations led to the formation of intrasubunit interactions between the N-terminus and the inhibitory peptide of cTnI. This may result in altered interactions with cTnC and could explain the increased rate and decreased duration of slow-phase relaxation seen in myofibrils.
authors.affiliation: Department of Bioengineering, University of Washington, Seattle, Washington; National Biomedical Computational Resource, University of California, San Diego, La Jolla, California.
authors.forename: Yuanhua
authors.initials: Y
authors.lastname: Cheng
authors.affiliation: National Biomedical Computational Resource, University of California, San Diego, La Jolla, California; Department of Pharmacology, University of California, San Diego, La Jolla, California.
authors.forename: Steffen
authors.initials: S
authors.lastname: Lindert
authors.affiliation: National Biomedical Computational Resource, University of California, San Diego, La Jolla, California; Department of Pharmacology, University of California, San Diego, La Jolla, California.
authors.forename: Peter
authors.initials: P
authors.lastname: Kekenes-Huskey
authors.affiliation: Department of Bioengineering, University of Washington, Seattle, Washington.
authors.forename: Vijay S
authors.initials: VS
authors.lastname: Rao
authors.affiliation: Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, Chicago, Illinois.
authors.forename: R John
authors.initials: RJ
authors.lastname: Solaro
authors.affiliation: Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, Ohio.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Rosevear
authors.affiliation: National Biomedical Computational Resource, University of California, San Diego, La Jolla, California.
authors.forename: Rommie
authors.initials: R
authors.lastname: Amaro
authors.affiliation: National Biomedical Computational Resource, University of California, San Diego, La Jolla, California; Department of Bioengineering, University of California, San Diego, La Jolla, California.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: McCulloch
authors.affiliation: National Biomedical Computational Resource, University of California, San Diego, La Jolla, California; Department of Pharmacology, University of California, San Diego, La Jolla, California.
authors.forename: J Andrew
authors.initials: JA
authors.lastname: McCammon
authors.affiliation: Department of Bioengineering, University of Washington, Seattle, Washington. Electronic address: mregnier@uw.edu.
authors.forename: Michael
authors.initials: M
authors.lastname: Regnier
mesh_terms: D002118:Calcium / Q000378:metabolism; D006801:Humans; D056004:Molecular Dynamics Simulation; D050505:Mutant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009206:Myocardium / Q000378:metabolism*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000378:metabolism; D019209:Troponin C / Q000737:chemistry / Q000378:metabolism; D019210:Troponin I / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D050505:Mutant Proteins; D021122:Protein Subunits; D019209:Troponin C; D019210:Troponin I; D002118:Calcium