A New Crystal Form of Tropomyosin

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Abstract
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 Å, c = 509 Å, and the symmetry is either P41212 or P43212, with 41(43) helical axes parallel to the c-axis. This suggests that a group of molecules surrounding a local 41 (43) 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.