Conformational flexibility of fork-remodeling helicase Rad5 shown by full-ensemble hybrid methods

Several pathways exist to bypass DNA damage during replication. One such pathway is template switching. The Rad5 protein plays two important roles in template switching: it is an E3 ubiquitin ligase that catalyzes PCNA poly-ubiquitylation and it is a helicase that converts replication forks to chicken foot structures. To understand the structure, conformational flexibility, and mechanism of Rad5, we used a full-ensemble hybrid method combining Langevin dynamics simulations and small-angle X-ray scattering. From these studies, we generated the first experimentally validated, high-resolution structural model of Rad5. We found that Rad5 is more compact and less extended than is suggested by its large amount of predicted intrinsic disorder. Thus, Rad5 likely has a novel intra-molecular interaction that limits the range of conformational space it can sample. We provide evidence for a novel interaction between the HIRAN and the helicase domains of Rad5, and we discuss the biological and mechanistic implications of this.