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Nature Structural & Molecular Biology 14, 921–926 (1 October 2007) | doi:10.1038/nsmb1300

The structure of bacterial ParM filaments

Albina Orlova , Ethan C Garner , Vitold E Galkin , John Heuser , R Dyche Mullins & Edward H Egelman

Bacterial ParM is a homolog of eukaryotic actin and is involved in moving plasmids so that they segregate properly during cell division. Using cryo-EM and three-dimensional reconstruction, we show that ParM filaments have a different structure from F-actin, with very different subunit-subunit interfaces. These interfaces result in the helical handedness of the ParM filament being opposite to that of F-actin. Like F-actin, ParM filaments have a variable twist, and we show that this involves domain-domain rotations within the ParM subunit. The present results yield new insights into polymorphisms within F-actin, as well as the evolution of polymer families.