Structural basis for activation and mechanism of the bacterial hexameric motors RadA and ComM in DNA branch migration during homologous recombination

Some DNA helicases play key roles in genome maintenance and plasticity through their branch migration activity in distinct pathways of homologous recombination. RadA is a highly conserved bacterial helicase involved in both DNA repair in all species and in natural transformation in Gram positive firmicutes. In others, ComM is the natural transformation-specific helicase. Both RadA and ComM form hexameric rings and use ATP hydrolysis as a source of energy. In this work we present the cryoEM structures of RadA and ComM interacting with DNA and ATP analogues. This is the first structure reported for ComM, and the first structure of RadA in its active state. In particular, this study unveiled a molecular switch for ATP hydrolysis and DNA binding coupling in RadA and the role of the Lon protease-like domain, shared by RadA and ComM. Together our results provide new insights on the branch migration mechanism at the molecular level in the context of homologous recombination.