Novel actin filaments fromBacillus thuringiensisform nanotubules for plasmid DNA segregation

Abstract

Here we report the discovery of a bacterial DNA-segregating actin-like protein (BtParM) fromBacillus thuringiensis, which forms novel antiparallel, two-stranded, supercoiled, nonpolar helical filaments, as determined by electron microscopy. TheBtParM filament features of supercoiling and forming antiparallel double-strands are unique within the actin fold superfamily, and entirely different to the straight, double-stranded, polar helical filaments of all other known ParMs and of eukaryotic F-actin. TheBtParM polymers show dynamic assembly and subsequent disassembly in the presence of ATP.BtParR, the DNA-BtParM linking protein, stimulated ATP hydrolysis/phosphate release byBtParM and paired two supercoiledBtParM filaments to form a cylinder, comprised of four strands with inner and outer diameters of 57 Å and 145 Å, respectively. Thus, in this prokaryote, the actin fold has evolved to produce a filament system with comparable features to the eukaryotic chromosome-segregating microtubule.