Structure of a tropomyosin N-terminal fragment at 0.98 Å resolution

Tropomyosin (TM) is an elongated two-chain protein that binds along actin filaments. Important binding sites are localized in the N-terminus of tropo­myosin. The structure of the N-terminus of the long muscle α-TM has been solved by both NMR and X-ray crystallography. Only the NMR structure of the N-­terminus of the short nonmuscle α-TM is available. Here, the crystal structure of the N-terminus of the short nonmuscle α-TM (αTm1bZip) at a resolution of 0.98 Å is reported, which was solved from crystals belonging to space group P3₁ with unit-cell parameters a = b = 33.00, c = 52.03 Å, α = β = 90, γ = 120°. The first five N-­terminal residues are flexible and residues 6–35 form an α-helical coiled coil. The overall fold and the secondary structure of the crystal structure of αTM1bZip are highly similar to the NMR structure and the atomic coordinates of the corresponding C^α atoms between the two structures superimpose with a root-mean-square deviation of 0.60 Å. The crystal structure validates the NMR structure, with the positions of the side chains being determined precisely in our structure.