The mechanisms responsible for switching muscle on and off and regulating its force and shortening will be studied. Current theories indicate that contraction is initiated by the binding of calcium to the regulatory protein complex, troponin and tropomyosin, and on the thin filament. The binding of calcium of troponin is thought to produce a movement of tropomyosin in such a fashion that charged sites on the actin and myosin are exposed and permitted to interact with myosin, resulting strong binding of the myosin head to the actin filament. This binding then initiates the force production and shortening in a fashion involving the use of ATP. The amount of force produced is thought to be dependent on the number of actin sites exposed while the unloaded shortening velocity is independent of the extent of thin filament activation. By combining measurement of the rate of shortening of single regulated thin filaments and the force exerted on single regulated thin filaments by myosin under a variety of conditions with site directed mutagenesis of the proteins involved in regulation, we plan to directly test hypotheses concerning: how many actin sites need to be switched on to activate contraction; how tropomyosin blocks the interaction surfaces of actin and myosin; whether mechanisms currently believed to modulate activation of the actin and myosin in the test tube can produce alterations in actomyosin s mechanical behavior; and whether the weak and strong binding sites on actin and myosin determine how much force or how fast the muscle shortens. Using the same techniques we will use mutant regulatory proteins known to be associated with hypertrophic cardiomyopathy to determine how these mutations alter cardiac muscle s ability to develop force and shorten.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Research Project (R01)
Project #
Application #
Study Section
Physiology Study Section (PHY)
Program Officer
Lymn, Richard W
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of California Los Angeles
Schools of Medicine
Los Angeles
United States
Zip Code
Siththanandan, V B; Tobacman, L S; Van Gorder, N et al. (2009) Mechanical and kinetic effects of shortened tropomyosin reconstituted into myofibrils. Pflugers Arch 458:761-76
Sumandea, Marius P; Vahebi, Susan; Sumandea, C Amelia et al. (2009) Impact of cardiac troponin T N-terminal deletion and phosphorylation on myofilament function. Biochemistry 48:7722-31
Pavlov, Dmitry; Gerson, Jack H; Yu, Tianwei et al. (2003) The regulation of subtilisin-cleaved actin by tropomyosin/troponin. J Biol Chem 278:5517-22
Piroddi, N; Tesi, C; Pellegrino, M A et al. (2003) Contractile effects of the exchange of cardiac troponin for fast skeletal troponin in rabbit psoas single myofibrils. J Physiol 552:917-31
Burkart, Eileen M; Sumandea, Marius P; Kobayashi, Tomoyoshi et al. (2003) Phosphorylation or glutamic acid substitution at protein kinase C sites on cardiac troponin I differentially depress myofilament tension and shortening velocity. J Biol Chem 278:11265-72
Homsher, E; Nili, M; Chen, I Y et al. (2003) Regulatory proteins alter nucleotide binding to acto-myosin of sliding filaments in motility assays. Biophys J 85:1046-52
Tobacman, Larry S; Nihli, Mahta; Butters, Carol et al. (2002) The troponin tail domain promotes a conformational state of the thin filament that suppresses myosin activity. J Biol Chem 277:27636-42
Karibe, A; Tobacman, L S; Strand, J et al. (2001) Hypertrophic cardiomyopathy caused by a novel alpha-tropomyosin mutation (V95A) is associated with mild cardiac phenotype, abnormal calcium binding to troponin, abnormal myosin cycling, and poor prognosis. Circulation 103:65-71
Strand, J; Nili, M; Homsher, E et al. (2001) Modulation of myosin function by isoform-specific properties of Saccharomyces cerevisiae and muscle tropomyosins. J Biol Chem 276:34832-9
Gordon, A M; Regnier, M; Homsher, E (2001) Skeletal and cardiac muscle contractile activation: tropomyosin ""rocks and rolls"". News Physiol Sci 16:49-55

Showing the most recent 10 out of 31 publications