Many Families of Lids for TonB-dependent Transporters in Bacteroides
Most TonB-dependent transporters in Bacteroides belong to the SusC family and work with an outer-membrane lipoprotein from the SusD family that functions like a lid. But the best-studied strain, B. thetaiotaomicron VPI-5482, also contains 18 TonB-dependent transporters that are not from the SusC family. We identified six families of putative lids for these transporters. The putative lids are lipoproteins that are encoded next to TonB-dependent transporters, but they are not homologous to SusD. AlphaFold-Multimer predicts that the putative lids bind the outer faces of the corresponding TonB-dependent receptors. Genetic data suggests that members of four of these families are required for the activity of the corresponding TonB-dependent receptors. Overall, of the 18 TonB-dependent receptors that do not belong to the SusC family, we identified alternate lids for nine.