Anaerobic C₄-dicarboxylate uptake/efflux porter, DcuB. Also catalyzes substrate:substrate antiport (fumarate:malate or fumarate:succinate antiport), but it is also a cosensor for the sensor kinase, DcuS (Kleefeld et al. 2009; Bauer et al. 2011; Chen et al. 2014) It has 12 established TMSs where the loop between TMSs 11 and 12 is the sensor. A central water-filled cavity may provide the transport pathway. The sensory domain of DcuB is composed of cytoplasmic loop XI/XII and a membrane integral region with the regulatory residues Thr396/Asp398 and Lys353. Also transports D-tartrate (Bauer et al. 2011; Kim et al. 2007).  The DcuB-DcuS interaction has been reviewed (Unden et al. 2016). The DcuS-DcuR two component system (sensor kinase-response regulator) responds to C₄-dicarboxylates in a process that requires formation of the complex of DcuS with C₄-dicarboxylate transporters DctA or DcuB (Bauer et al. 2011; Chen et al. 2014) It has 12 established TMSs where the loop between TMSs 11 and 12 is the sensor. A central water-filled cavity may provide the transport pathway. The sensory domain of DcuB is composed of cytoplasmic loop XI/XII and a membrane integral region with the regulatory residues Thr396/Asp398 and Lys353. Also transports D-tartrate (Bauer et al. 2011; Kim et al. 2007).  The DcuB-DcuS interaction has been reviewed (Unden et al. 2016). The DcuS-DcuR two component system (sensor kinase-response regulator) responds to C₄-dicarboxylates in a process that requires formation of the complex of DcuS with C₄-dicarboxylate transporters DctA or DcuB (Wörner et al. 2018).