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.
