Functional implications of arginine-121 in RuvA oligomerisation and RuvAB-mediated branch migration in the Gram-positive Listeria monocytogenes

In prokaryotes, the RuvAB complex drives Holliday junction (HJ) branch
migration, but the relative importance of RuvA tetramers versus octamers
remains debatable and unexplored in Gram-positive bacteria. In this study,
we aimed to determine whether RuvA from Listeria monocytogenes
(LmRuvA) is active as a tetramer or octamer in branch migration. We identi-
fied arginine-121 as being critical for the formation of the tetramer–tetramer
interface. Mutation of arginine-121 to aspartate results in a protein that
exists in a dimer to tetramer equilibrium in solution (unlike other octamer-
deficient mutants from earlier studies), binds to the HJ as a tetramer only,
interacts poorly with RuvB, and cannot catalyse branch migration. Collec-
tively, these findings suggest that the ability of LmRuvA to bind HJs as an
octamer is critical to branch migration.