Tol Energy-Driven Localization of Pal and Anchoring to the Peptidoglycan Promote Outer-Membrane Constriction.

During cell division, gram-negative bacteria must coordinate inner-membrane invagination, peptidoglycan synthesis and cleavage and outer-membrane (OM) constriction. The OM constriction remains largely enigmatic, and the nature of this process, passive or active, is under debate. The proton-motive force-dependent Tol-Pal system performs a network of interactions within these three compartments. Here we confirm that the trans-envelope Tol-Pal complex accumulates at constriction site in Escherichia coli. We show that the inner-membrane complex composed of TolA, TolQ and TolR recruits the OM complex TolB-Pal to the septum, in an energy-dependent process. Pal recruitment then allows its binding to peptidoglycan and subsequently OM constriction. Our results provide evidence that the constriction of the OM is an energized process.