C4-dicarboxylate carriers and sensors in bacteria

Bacteria contain secondary carriers for the uptake, exchange or efflux of C-4-dicarboxylates. In aerobic bacteria, dicarboxylate transport (Dct)A carriers catalyze uptake of C-4-dicarboxylates in a H+- or Na+-C-4-dicarboxylate symport. Carriers of the dicarboxylate uptake (Dcu)AB family are used for electroneutral fumarate:succinate antiport which is required in anaerobic fumarate respiration. The DcuC carriers apparently function in succinate efflux during fermentation. The tripartite ATP-independent periplasmic (TRAP) transporter carriers are secondary uptake carriers requiring a periplasmic solute binding protein. For heterologous exchange of(4)-dicarboxylates with other carboxylic acids (such as citrate:succinate by CitT) further types of carriers are used. The different families Of C-4-dicarboxylate carriers, the biochemistry of the transport reactions, and their metabolic functions are described. Many bacteria contain membraneous C-4-dicarboxylate sensors which control the synthesis of enzymes for C-4-dicarboxylate metabolism. The C-4-dicarboxylate sensors DcuS, DctB, and DctS are histidine protein kinases. and belong to different families of two-component systems. They contain periplasmic domains presumably involved in C-4-dicarboxylate sensing. In DcuS the periplasmic domain seems to be essential for direct interaction with the C-4-dicarboxylates. In signal perception by DctB. interaction of the C-4-dicarboxylates with DctB and the DctA carrier plays an important role. (C) 2002 Elsevier Science B.V. All rights reserved.