Modulation of the effects of tropomyosin on actin and myosin conformational changes by troponin and Ca2+.

Journal article

The molecular mechanisms by which troponin (TN)-tropomyosin (TM) regulates the myosin ATPase cycle were investigated using fluorescent probes specifically bound to Cys36 of TM, Cys707 of myosin subfragment-1, and Cys374 of actin incorporated into ghost muscle fibers. Intermediate states of actomyosin were simulated by using nucleotides and non-hydrolysable ATP analogs. Multistep changes in mobility and spatial arrangement of SH1 helix of myosin motor domain and actin subdomain-1 during the ATPase cycle were observed. Each intermediate state of actomyosin induced a definite conformational state and specific position of TM strands on the surface of thin filament. TM increased the amplitude of myosin SH1 helix and actin subdomain-1 movements at transition from weak- to strong-binding states shifting to the center of thin filament at strong-binding and to the periphery of thin filament at weak-binding states. TN modulated those movements in a capital ES, Cyrillicsmall a, Cyrillic(2+)-dependent manner. At high-Ca(2+), TN enhanced the effect of TM on SH1 helix and subdomain-1 movements by transferring TM further to the center of thin filament at strong-binding states. In contrast, at low-Ca(2+), TN inhibited the effect of TM movements, "freezing" actin structure in "OFF" state and TM in the position typical for weak-binding states, resulting in disturbing the interplay of actin and myosin.

Authors: Borovikov, Y; Karpicheva, O; Avrova, S; Redwood, C

• Publication status: Published
• Journal: Biochimica et biophysica acta
• Volume: 1794
• Issue: 7
• Pages: 985-994
• Publication date: 2009-07-01
• DOI: 10.1016/j.bbapap.2008.11.014
• ISSN: 0006-3002
• Language: English
• Keywords: Tropomyosin; Protein Conformation; Calcium; Animals; Fluorescent Dyes; Rabbits; Myosins; Actins; Fluorescence Polarization