Part of the Tol-Pal system, which plays a role in outer membrane invagination during cell division and is important for maintaining outer membrane integrity (PubMed:17233825). TolB occupies a key intermediary position in the Tol-Pal system because it communicates directly with both membrane-embedded components, Pal in the outer membrane and TolA in the inner membrane (PubMed:19696740). The Tol-Pal system is also required for polar localization of chemoreceptors clusters (PubMed:24720726). The system also appears to be required for the activity of several outer membrane-localized enzymes with cell wall remodeling activity (PubMed:32152098). Is involved in the uptake of some colicins A (PubMed:2687247, PubMed:7929011, PubMed:11994151). The Tol-Pal system is composed of five core proteins: the inner membrane proteins TolA, TolQ and TolR, the periplasmic protein TolB and the outer membrane protein Pal. They form a network linking the inner and outer membranes and the peptidoglycan layer (PubMed:17233825). TolB forms homodimers (PubMed:11994151). Interacts with the peptidoglycan-associated lipoprotein Pal and with the C-terminal region of TolA (PubMed:7744736, PubMed:11994151, PubMed:17375930, PubMed:19696740). Interacts with the trimeric porins OmpF, OmpC, PhoE and LamB (PubMed:9393690). Can form a complex with Pal, Lpp and OmpA (PubMed:9701827). Interacts with colicin E9 (PubMed:10673426, PubMed:16894158). Partially associated with the outer membrane through a specific interaction with Pal (PubMed:7744736). Accumulates at cell constriction sites. Recruitment to the division site is dependent on FtsN activity (PubMed:17233825). Effector proteins that bind to TolB can both negatively (Pal) and positively (colicin E9) regulate association of the distal N-terminal TolA box with TolA by influencing the conformational equilibrium experienced by these residues. Mutants lacking the tol-pal cluster suffer delayed outer membrane invagination and contain large outer membrane blebs at constriction sites and cell poles (PubMed:17233825). Tol-pal mutants fail to complete division and form cell chains, and fail to process denuded peptidoglycans at the septum (PubMed:32152098). Belongs to the TolB family.