title: TRAP transporters: an ancient family of extracytoplasmic solute-receptor-dependent secondary active transporters.
abstract: Tripartite ATP-independent periplasmic transporters (TRAP-T) represent a novel type of secondary active transporter that functions in conjunction with an extracytoplasmic solute-binding receptor. The best characterized TRAP-T family member is from Rhodobacter capsulatus and is specific for C4-dicarboxylates [Forward, J. A., Behrendt, M. C., Wyborn, N. R., Cross, R. & Kelly, D. J. (1997). J Bacteriol 179, 5482-5493]. It consists of three essential proteins, DctP, a periplasmic C4-dicarboxylate-binding receptor, and two integral membrane proteins, DctM and DctQ, which probably span the membrane 12 and 4 times, respectively. Homologues of DctM, DctP and DctQ were identified in all major bacterial subdivisions as well as in archaea. An orphan DctP homologue in the Gram-positive bacterium Bacillus subtilis may serve as a receptor for a two-component transcriptional regulatory system rather than as a constituent of a TRAP-T system. Phylogenetic data suggest that all present day TRAP-T systems probably evolved from a single ancestral transporter with minimal shuffling of constituents between systems. Homologous TRAP-T constituents exhibit decreasing degrees of sequence identity in the order DctM > DctP > DctQ. DctM appears to belong to a large superfamily of transporters, the ion transporter (IT) superfamily, one member of which can function by either protonmotive force- or ATP-dependent energization. It is proposed that IT superfamily members exhibit the unusual capacity to function in conjunction with auxiliary proteins that modify the transport process by providing (i) high-affinity solute reception, (ii) altered energy coupling and (iii) additional yet to be defined functions.
authors.affiliation: Department of Biology, University of California at San Diego, La Jolla, CA, 92093-0116, USA1.
authors.forename: Ralf
authors.initials: R
authors.lastname: Rabus
authors.affiliation: Department of Biology, University of California at San Diego, La Jolla, CA, 92093-0116, USA1.
authors.forename: Donald L
authors.initials: DL
authors.lastname: Jack
authors.affiliation: Krebs Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2UH, UK 2.
authors.forename: David J
authors.initials: DJ
authors.lastname: Kelly
authors.affiliation: Department of Biology, University of California at San Diego, La Jolla, CA, 92093-0116, USA1.
authors.forename: Milton H
authors.initials: MH
authors.lastname: Saier
mesh_terms: D000595:Amino Acid Sequence; D001105:Archaea / Q000235:genetics* / Q000378:metabolism; D001419:Bacteria / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D029382:Dicarboxylic Acid Transporters; D019143:Evolution, Molecular; D017136:Ion Transport; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D033903:Periplasmic Proteins; D010802:Phylogeny
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C108091:DctM protein, Rhodobacter capsulatus; C108092:DctQ protein, Rhodobacter capsulatus; D029382:Dicarboxylic Acid Transporters; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033903:Periplasmic Proteins; C074174:DctP protein, Rhodobacter capsulatus