A new crystal form of tropomyosin. Preliminary X-ray diffraction analysis

A new crystalline form of tropomyosin has been produced that diffracts to about 4 A resolution. The crystals are grown at room temperature by slowly lowering the concentration of spermine. This polyamine apparently neutralizes the acidic amino acid side-chains of tropomyosin and allows close side-by-side packing of molecules. The space group is C2, with unit cell dimensions a = 259.7 A, b = 55.3 A, c = 135.6 A, and beta = 97.2 degrees. The tropomyosin molecules appear to be bonded head-to-tail to form straight filaments that run along the crystallographic (332) direction in an arrangement closely related to thin crystalline sheets previously described.