Figure 2.

TonB-dependent transporters and ABC transport systems produced by the pathogenic Neisseria species. Barrel shapes in the outer membrane (OM) are meant to represent the eight TonB-dependent transporters produced by the Neisseriae. Three systems, Tbp, Lbp and Hpu, also include a lipoprotein component (TbpB, LbpB and HpuA, respectively), which are shown tethered to the outer membrane by a lipid moiety. Ligands for each system are described in the text. Black lines extending from the outer membrane are meant to represent lipooligosaccharide. The peptidoglycan layer is shown in the periplasm. The TonB, ExbB and ExpD proteins are shown tethered to or integral in the cytoplasmic membrane (CM). This system energizes transport through the outer membrane by the TonB-dependent transporters. Three ABC transport systems are also represented. FbpABC transports ferric iron; FetBCD transports catecholate siderophores; ZnuABC (sometimes referred to as MntABC in the literature) transports zinc and manganese.