Role of actin C-terminus in regulation of striated muscle thin filament.
In striated muscle, regulation of actin-myosin interactions depends on a series of conformational changes within the thin filament that result in a shifting of the tropomyosin-troponin complex between distinct locations on actin. The major factors activating the filament are Ca(2+) and strongly bound myosin heads. Many lines of evidence also point to an active role of actin in the regulation. Involvement of the actin C-terminus in binding of tropomyosin-troponin in different activation states and the regulation of actin-myosin interactions were examined using actin modified by proteolytic removal of three C-terminal amino acids. Actin C-terminal modification has no effect on the binding of tropomyosin or tropomyosin-troponin + Ca(2+), but it reduces tropomyosin-troponin affinity in the absence of Ca(2+). In contrast, myosin S1 induces binding of tropomyosin to truncated actin more readily than to native actin. The rate of actin-activated myosin S1 ATPase activity is reduced by actin truncation both in the absence and presence of tropomyosin. The Ca(2+)-dependent regulation of the ATPase activity is preserved. Without Ca(2+) the ATPase activity is fully inhibited, but in the presence of Ca(2+) the activation does not reach the level observed for native actin. The results suggest that through long-range allosteric interactions the actin C-terminus participates in the thin filament regulation.
Sliwinska
Malgorzata
M
Kazimierz Wielki University in Bydgoszcz, Department of Experimental Biology, Bydgoszcz, Poland.
Skórzewski
Radoslaw
R
Moraczewska
Joanna
J
D000199:Actins / Q000737:chemistry*; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry*; D008956:Models, Chemical; D020409:Molecular Motor Proteins / Q000737:chemistry*; D018485:Muscle Fibers, Skeletal / Q000737:chemistry*; D009218:Myosins / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation
D000199:Actins; D020409:Molecular Motor Proteins; D009218:Myosins; D002118:Calcium