Precise Binding of Tropomyosin on Actin Involves Sequence-Dependent Variance in Coiled-coil Twisting

Often considered an archetypal dimeric coiled-coil, tropomyosin nonetheless exhibits distinctive "non-canonical" core residues located at the hydrophobic interface between its component α-helices. Notably, a charged aspartate, D137, takes the place of non-polar residues otherwise present. Much speculation has been offered to rationalize potential local coiled-coil instability stemming from D137 and its effect on regulatory transitions of tropomyosin over actin filaments. While experimental approaches such as cryo-EM reconstruction are optimal for defining average tropomyosin positions on actin filaments, to date, these methods have not captured the dynamics of tropomyosin residues clustered around position 137 or elsewhere.

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