TY - JOUR AB - Elongated tropomyosin, associated with actin-subunits along the surface of thin filaments, makes electrostatic interactions with clusters of conserved residues, K326, K328, and R147, on actin. The association is weak, permitting low-energy cost regulatory movement of tropomyosin across the filament during muscle activation. Interestingly, acidic D292 on actin, also evolutionarily conserved, lies adjacent to the three-residue cluster of basic amino acids and thus may moderate the combined local positive charge, diminishing tropomyosin-actin interaction and facilitating regulatory-switching. Indeed, charge neutralization of D292 is connected to muscle hypotonia in individuals with D292V actin mutations and linked to congenital fiber-type disproportion. Here, the D292V mutation may predispose tropomyosin-actin positioning to a myosin-blocking state, aberrantly favoring muscle relaxation, thus mimicking the low-Ca2+ effect of troponin even in activated muscles. To test this hypothesis, interaction energetics and in vitro function of wild-type and D292V filaments were measured. Energy landscapes based on F-actin-tropomyosin models show the mutation localizes tropomyosin in a blocked-state position on actin defined by a deeper energy minimum, consistent with augmented steric-interference of actin-myosin binding. In addition, whereas myosin-dependent motility of troponin/tropomyosin-free D292V F-actin is normal, motility is dramatically inhibited after addition of tropomyosin to the mutant actin. Thus, D292V-induced blocked-state stabilization appears to disrupt the delicately poised energy balance governing thin filament regulation. Our results validate the premise that stereospecific but necessarily weak binding of tropomyosin to F-actin is required for effective thin filament function. AU - Rynkiewicz,MJ AU - Prum,T AU - Hollenberg,S AU - Kiani,FA AU - Fagnant,PM AU - Marston,SB AU - Trybus,KM AU - Fischer,S AU - Moore,JR AU - Lehman,W DO - 10.1016/j.bpj.2017.10.004 EP - 2451 PY - 2017/// SN - 0006-3495 SP - 2444 TI - Tropomyosin Must Interact Weakly with Actin to Effectively Regulate Thin Filament Function. T2 - Biophysical Journal UR - http://dx.doi.org/10.1016/j.bpj.2017.10.004 UR - http://hdl.handle.net/10044/1/55291 VL - 113 ER -