Structural elements required for the efficient loading and activation of HELB on RPA-coated single-stranded DNA

HELB is a human helicase involved in DNA repair and replication that interacts physically with the single-stranded DNA binding protein RPA. ATP-dependent translocation of HELB along ssDNA results in the active displacement of RPA molecules and the formation of ssDNA loops, suggesting that HELB contains at least two DNA binding sites. In this work, we investigated the role of HELB-specific structural elements in facilitating interactions between HELB and RPA-coated DNA. We show that a predicted OB-fold in the N-terminal region of the protein is important both for loop extrusion and RPA displacement. We confirm that a HELB-specific-motif within the RecA-like helicase/translocase domains is critical for binding RPA in solution but that, once HELB is bound to ssDNA, is dispensable for RPA displacement. We propose a model for RPA displacement in which both structural elements play important roles in the recruitment and activation of HELB at RPA-ssDNA filaments.