Mediates coordination of peptidoglycan synthesis and outer membrane constriction during cell division. Promotes physical and functional coordination of the PBP1B-LpoB and Tol machines, and regulates PBP1B activity in response to Tol energy state. Homotrimer (PubMed:20455268, PubMed:20816983). Interacts directly with the central domain of TolA and with PBP1B (PubMed:11994151, PubMed:20816983, PubMed:25951518). Binding to TolA disrupts the homotrimer to form a YbgF/TolA heterodimer with weak affinity (PubMed:20816983). Forms a quaternary complex with PBP1B-LpoB and TolA (PubMed:25951518). Targeting to the Sec-translocase for transport across the inner membrane is SecB-dependent (PubMed:16352602). Localizes to the septum concurrent with PBP1B-LpoB and Tol at the onset of constriction (PubMed:25951518). Localization is dependent on divisome assembly and requires ongoing septal peptidoglycan synthesis (PubMed:25951518). Contains an N-terminal coiled-coil domain and a C-terminal TPR domain, separated by a flexible linker. The N-terminal domain forms a stable trimer and controls the oligomeric status. The C-terminal domain, which can also trimerize, is involved in interaction with TolA. Deletion mutant is sensitive to multiple beta-lactams, including cefsulodin. It leads to defects in outer membrane integrity, envelope defects and elevated cell lysis. Belongs to the CpoB family.