Calcium-induced movement of troponin-I relative to actin in skeletal muscle thin filaments.
The role of troponin-I (the inhibitory subunit of troponin) in the regulation by Ca2+ of skeletal muscle contraction was investigated with resonance energy transfer and photo cross-linking techniques. The effect of Ca2+ on the proximity of troponin-I to actin in reconstituted rabbit skeletal thin filaments was determined. The distance between the cysteine residue at position 133 (Cys133) of troponin-I and Cys374 of actin increases by approximately 15 angstroms on binding of Ca2+ to troponin-C. Also, troponin-I labeled at Cys133 with benzophenone-4-maleimide could be photo cross-linked to actin in the absence of Ca2+, but not in its presence. These results suggest that troponin-I is attached to actin in the Ca2(+)-free or relaxed state of muscle, and that it detaches from actin on Ca2+ activation of contraction. Thus, troponin-I may function as a Ca2(+)-dependent molecular switch in regulation of skeletal muscle contraction.
Tao
T
T
Department of Muscle Research, Boston Biomedical Research Institute, MA 02114.
Gong
B J
BJ
Leavis
P C
PC
D000199:Actins / Q000502:physiology*; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000502:physiology*; D003545:Cysteine; D066298:In Vitro Techniques; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D009218:Myosins / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D014336:Troponin / Q000502:physiology*; D019210:Troponin I
D000199:Actins; D014336:Troponin; D019210:Troponin I; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins; D003545:Cysteine; D002118:Calcium