Competitive binding of MatP and topoisomerase IV to the MukB dimerization hinge

Abstract

SMC complexes have ubiquitous roles in chromosome organisation. In Escherichia coli, the interplay between the SMC complex, MukBEF, and matS-bound MatP in the replication termination region, ter, results in depletion of MukBEF from ter, thus promoting chromosome individualisation by directing replichores to separate cell halves. MukBEF also interacts with topoisomerase IV ParC2E2 heterotetramers, to direct its chromosomal distribution to mirror that of MukBEF, thereby facilitating coordination between chromosome organisation and decatenation by topoisomerase IV. Here we demonstrate that the MukB dimerization hinge binds ParC and MatP with the same dimer to dimer stoichiometry. MatP and ParC have an overlapping binding interface on the MukB hinge, leading to their mutually exclusive binding. Furthermore, the MukB hinge fails to stably associate with matS-bound MatP, while MatP mutants deficient in matS binding are impaired in MukB hinge binding, demonstrating that mats competes with the hinge for MatP binding. Cells expressing MukBEF complexes containing a mutation in the MukB hinge interface for ParC/MatP binding are deficient in ParC binding in vivo, despite having a Muk+ topoisomerase IV+ phenotype. This mutant protein is also impaired in MatP binding in vitro, and cells expressing this variant exhibit a MukBEF cellular localisation consistent with impaired MatP binding.