ИСТИНА

It was hypothesized early that the well conserved non-canonical residue Gly-126 causes local destabilization of Tm. To test this, we labeled Cys190 of wild-type and Gly126Arg mutant a-tropomyosins with the fluorescent probe 5-IAF, and Cys707 of myosin subfragment- 1 and Cys374 of actin with 1.5-IAEDANS and F-actin with FITCphalloidin. These proteins were incorporated into ghost muscle fibres and their conformational states were monitored during the ATPase cycle by measuring polarized fluorescence. Wild-type a-tropomyosin increases the amplitude of the SH1 helix, subdomain-1 and actin monomer movements during the ATPase cycle, indicating the enhancement of the efficiency of the work of cross-bridges. The Gly126Arg mutation shifted tropomyosin further towards the open position, showing an increase in the binding of strong cross-bridges to actin during the ATPase cycle. We propose that the highly conserved Gly-126 destabilizes the middle part of Tm, resulting in the concerted conformational changes of actomyosin. It is possible that the movement of mutant TM strands further towards the center of the thin filament is a reason for the enhancement of the strong-binding states during the ATPase cycle. Supported by the Russian Fund for Fundamental Research N.11-04-00244 and the Program 7 of the Presidium of the Russian Academy of Sciences.