title: Conserved Asp-137 is important for both structure and regulatory functions of cardiac α-tropomyosin (α-TM) in a novel transgenic mouse model expressing α-TM-D137L.
abstract: α-Tropomyosin (α-TM) has a conserved, charged Asp-137 residue located in the hydrophobic core of its coiled-coil structure, which is unusual in that the residue is found at a position typically occupied by a hydrophobic residue. Asp-137 is thought to destabilize the coiled-coil and so impart structural flexibility to the molecule, which is believed to be crucial for its function in the heart. A previous in vitro study indicated that the conversion of Asp-137 to a more typical canonical Leu alters flexibility of TM and affects its in vitro regulatory functions. However, the physiological importance of the residue Asp-137 and altered TM flexibility is unknown. In this study, we further analyzed structural properties of the α-TM-D137L variant and addressed the physiological importance of TM flexibility in cardiac function in studies with a novel transgenic mouse model expressing α-TM-D137L in the heart. Our NMR spectroscopy data indicated that the presence of D137L introduced long range rearrangements in TM structure. Differential scanning calorimetry measurements demonstrated that α-TM-D137L has higher thermal stability compared with α-TM, which correlated with decreased flexibility. Hearts of transgenic mice expressing α-TM-D137L showed systolic and diastolic dysfunction with decreased myofilament Ca(2+) sensitivity and cardiomyocyte contractility without changes in intracellular Ca(2+) transients or post-translational modifications of major myofilament proteins. We conclude that conversion of the highly conserved Asp-137 to Leu results in loss of flexibility of TM that is important for its regulatory functions in mouse hearts. Thus, our results provide insight into the link between flexibility of TM and its function in ejecting hearts.
authors.affiliation: Departments of Biochemistry and Molecular Genetics, Chicago, Illinois 60612; Physiology and Biophysics, Chicago, Illinois 60612.
authors.forename: Sumeyye
authors.initials: S
authors.lastname: Yar
authors.affiliation: Physiology and Biophysics, Chicago, Illinois 60612.
authors.forename: Shamim A K
authors.initials: SAK
authors.lastname: Chowdhury
authors.affiliation: Physiology and Biophysics, Chicago, Illinois 60612.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Davis
authors.affiliation: Physiology and Biophysics, Chicago, Illinois 60612.
authors.forename: Minae
authors.initials: M
authors.lastname: Kobayashi
authors.affiliation: Physiology and Biophysics, Chicago, Illinois 60612.
authors.forename: Michelle M
authors.initials: MM
authors.lastname: Monasky
authors.affiliation: Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267.
authors.forename: Sudarsan
authors.initials: S
authors.lastname: Rajan
authors.affiliation: Physiology and Biophysics, Chicago, Illinois 60612; Medicine, Chicago, Illinois 60612; Center for Cardiovascular Research, University of Illinois, Chicago, Illinois 60612.
authors.forename: Beata M
authors.initials: BM
authors.lastname: Wolska
authors.affiliation: Departments of Biochemistry and Molecular Genetics, Chicago, Illinois 60612.
authors.forename: Vadim
authors.initials: V
authors.lastname: Gaponenko
authors.affiliation: Physiology and Biophysics, Chicago, Illinois 60612; Center for Cardiovascular Research, University of Illinois, Chicago, Illinois 60612.
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267.
authors.forename: David F
authors.initials: DF
authors.lastname: Wieczorek
authors.affiliation: Physiology and Biophysics, Chicago, Illinois 60612; Center for Cardiovascular Research, University of Illinois, Chicago, Illinois 60612. Electronic address: solarorj@uic.edu.
authors.forename: R John
authors.initials: RJ
authors.lastname: Solaro
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D051379:Mice; D008822:Mice, Transgenic; D020125:Mutation, Missense; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D019906:Nuclear Magnetic Resonance, Biomolecular; D055550:Protein Stability; D051381:Rats; D013318:Stroke Volume; D013329:Structure-Activity Relationship; D014335:Tropomyosin / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics
chemical_list: D014335:Tropomyosin
keywords: Actin; Cardiac Muscle; Cardiovascular Disease; Flexibility; Mouse Model; Muscle; Thin Filament; Transgenic; Tropomyosin; Troponin