More insights into the dynamic assembly and rotation of the archaellum motor machinery

Archaea use the archaellum for swimming motility. Rotation of the archaellum is driven by the ATPase ArlI and the membrane platform protein ArlJ. Structural studies suggest that conformational changes in ArlI power the rotation of ArlJ. However, how ATP hydrolysis is converted into rotation remains poorly under-stood. Using single-molecule total internal reflection fluorescence (TIRF) microscopy, we show that dimeric ArlJ forms a complex with ArlI. Combining conservation analysis, AlphaFold3 predictions and co-purifications, we identified conserved ArlJ residues required for interaction with ArlI, including a structural-ly rigid loop and the critical residue R341 at the ArlI interface. Motility assays in Haloferax volcanii confirmed these findings. Together, these findings support a model in which a dimeric ArlJ is interacting with ArlI via conserved residues to generate torque.