Mtb UvrD1 monomer unwinds a Ku nucleoprotein filament.

Abstract

Mycobacterium tuberculosis is a causative agent of tuberculosis and during infection exposed to reactive oxygen species and reactive nitrogen intermediates from host immune response that causes DNA damage. We have previously shown that both monomers and dimers of Mtb UvrD1 can bind and translocate on single-stranded DNA, but only a redox-dependent dimer unwinds the DNA. Independent studies have shown that Ku, a factor involved in non-homologous end joining, increases the helicase activity of Mtb UvrD1. However, it's unknown if Ku enhances the helicase activity of monomer or dimer UvrD1. Here, we show that a monomer of UvrD1 can slowly (i.e. 100x slower than the dimer) unwind DNA in multiround conditions and Ku specifically enhances the helicase activity of UvrD1 monomers. We also show that the UvrD1 C-terminal domain is required for Ku-dependent activation, suggesting a protein-protein interaction between the two. Since we and others observe that Ku binds cooperatively to double-stranded DNA, these results suggest a model where a UvrD1 monomer unwinds DNA in the context of a Ku nucleoprotein filament. These results highlight the potential role of UvrD1 in multiple DNA repair pathways through different mechanisms of activation.