A new crystal form of tropomyosin.

Tropomyosin crystals with a new morphology have been obtained from lobster tail muscle tropomyosin from which 11 residues at the carboxyl-terminus have been proteolytically removed to avoid head-to-tail polymerization. In contrast to the conventional Bailey crystal form in which the elongated tropomyosin molecules form a mesh, in the present crystals the molecules are packed side-to-side with the long axes parallel to the c-axis of the crystal. The unit cell is tetragonal with a = b = 109 A, c = 509 A, and the symmetry is either P4(1)2(1)2 or P4(3)2(1)2, with 4(1)(4(3)) helical axes parallel to the c-axis. This suggests that a group of molecules surrounding a local 4(1)(4(3)) axis is regarded as the building unit of the crystal. It is likely that the unit cell contains eight molecules with one molecule per asymmetric unit.