Comparison of MukB homodimer versus MukBEF complex molecular architectures by electron microscopy reveals a higher-order multimerization

The complex of MukF, MukE, and MukB proteins participates in organization of sister chromosomes and partitioning into both daughter cells in Escherichia coli. We purified the MukB homodimer and the MukBEF complex and analyzed them by electron microscopy to compare both structures. A MukB homodimer shows a long rod-hinge-rod v-shape with small globular domains at both ends. The MukBEF complex shows a similar structure having larger globular domains than those of the MukB homodimer. These results suggest that MukF and MukE bind to the globular domains of a MukB homodimer. The globular domains of the MukBEF complex frequently associate with each other in an intramolecular fashion, forming a ring. In addition, MukBEF complex molecules tend to form multimers by the end-to-end joining with other MukBEF molecules in an intermolecular fashion, resulting in fibers and rosette-form structures in the absence of ATP and DNA in vitro.