DIRECT INTERACTION OF FLAGELLIN TERMINI ESSENTIAL FOR POLYMORPHIC ABILITY OF FLAGELLAR FILAMENT

We report the structures of flagellar filaments reconstituted from var ious flagellins with small terminal truncations, Flagellins from Salmo nella typhimurium strains SJW1103 (wild type), SJW1660, and SJW1655 we re used, which form a left-handed supercoil, the L- and R-type straigh t forms, respectively, Structure analyses were done by electron cryomi croscopy and helical image reconstruction with a help of x-ray fiber d iffraction for determining precise helical symmetries. Truncation of e ither terminal region, irrespective of the original flagellin species, results In a straight filament having a helical symmetry distinct eit her from the L- or R-type. This filament structure is named Lt-type. A lthough the focal subunit packing is similar in all three types, a clo se comparison shows that the Et-type packing is almost identical to th e R-type but distinct from the L-type, which demonstrates the strong t wo-stale preference of the subunit interactions, The structure clearly suggests that Both termini are located in the inner tube of the conce ntric double-tubular structure of the filament core, and their proper interaction is responsible for the correct folding of Fairly large ter minal regions that form the inner tube, The double tubular structure a ppears to be essential for the polymorphic ability of flagellar filame nts, which is required for the swimming-tumbling of bacterial taxis.