A skipping rope translocation mechanism in a widespread family of DNA repair helicases

Mitomycin repair factor A represents a family of DNA helicases that harbor a domain of unknown function DUF1998 and support repair of mitomycin Cinduced DNA damage by presently unknown molecular mechanisms. We determined crystal structures of Bacillus subtilis Mitomycin repair factor A alone and in complex with an ATP analog and or DNA and conducted structure informed functional analyses. Our results reveal a unique set of auxiliary domains appended to a dual RecA domain core. Upon DNA binding, a Zn2 binding domain, encompassing the domain of unknown function, acts like a drum that rolls out a canopy of helicase associated domains, entrapping the substrate and tautening an inter domain linker across the loading strand. Quantification of DNA binding, stimulated ATPase and helicase activities in the wild type and mutant enzyme variants in conjunction with themode of coordination of the ATP analog suggest that Mitomycin repair factor A employs similar ATPase driven conformational changes to translocate on DNA, with the linker ratcheting through the nucleotides like a skipping rope . The electrostatic surface topology outlines a likely path for the displaced DNA strand. Our results reveal unique molecular mechanisms in a widespread family of DNA repair helicases linked to bacterial antibiotics resistanc