Troponin I and troponin T interact with troponin C to produce different Ca2+-dependent effects on actin-tropomyosin filament motility.
We have developed an in vitro motility assay to make a detailed quantitative analysis of Ca2+ control of skeletal-muscle troponin-tropomyosin control of actin-filament movement over immobilized myosin. Ca2+ regulates both filament velocity and the fraction of filaments that are motile. We have demonstrated that the two effects are due to separate interactions of troponin C with troponin I and troponin T. When 64nM of the complex actin-tropomyosin-troponin I-troponin C was added at pCa 5, more than 80% of filaments were moving and their velocity did not change. At pCa 9, more than 20% of the filaments were moving. When 20nM of the complex actin-tropomyosin-troponin T+troponin I+troponin C was added at pCa 5, filament motility remained high, whereas velocity increased. The 30% increase in velocity observed when troponin T was present was also observed when heavy meromyosin fragment 1 labelled with N-ethylmaleimide (NEM S-1) was added after actin-tropomyosin filaments. The NEM S-1 effect was not additive with the troponin T-dependent velocity increase. The pattern of motile behaviour is characteristic of myosin on silicone-treated glass and different from the behaviour on nitrocellulose-coated glass.
Bing
W
W
Cardiac Medicine, Imperial College School of Medicine at the National Heart and Lung Institute, Dovehouse Street, London SW3 6LY, U.K.
Fraser
I D
ID
Marston
S B
SB
D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D007700:Kinetics; D018482:Muscle, Skeletal / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D011817:Rabbits; D012756:Sheep; D014335:Tropomyosin / Q000737:chemistry / Q000378:metabolism*; D014336:Troponin / Q000737:chemistry / Q000378:metabolism*; D019209:Troponin C / Q000737:chemistry / Q000378:metabolism*; D019210:Troponin I / Q000737:chemistry / Q000378:metabolism*; D020107:Troponin T
D000199:Actins; D014335:Tropomyosin; D014336:Troponin; D019209:Troponin C; D019210:Troponin I; D020107:Troponin T; D002118:Calcium