Structure of the bacterial flagellar protofilament and implications for a switch for supercoiling

Protonic NanoMachine Project, ERATO, JST, 3-4 Hikaridai, Seika, Kyoto 619-0237, Japan.
Nature (Impact Factor: 42.35). 03/2001; 410(6826):331-337. DOI: 10.1038/35066504

ABSTRACT The bacterial flagellar filament is a helical propeller constructed from 11 protofilaments of a single protein, flagellin. The filament switches between left- and right-handed supercoiled forms when bacteria switch their swimming mode between running and tumbling. Supercoiling is produced by two different packing interactions of flagellin called L and R. In switching from L to R, the intersubunit distance (52 Å) along the protofilament decreases by 0.8 Å. Changes in the number of L and R protofilaments govern supercoiling of the filament. Here we report the 2.0 Å resolution crystal structure of a Salmonella flagellin fragment of relative molecular mass 41,300. The crystal contains pairs of antiparallel straight protofilaments with the R-type repeat. By simulated extension of the protofilament model, we have identified possible switch regions responsible for the bi-stable mechanical switch that generates the 0.8 Å difference in repeat distance.

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