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      Novel Transporter Required for Biogenesis of cbb 3-Type Cytochrome c Oxidase in Rhodobacter capsulatus

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      mBio
      American Society of Microbiology

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          ABSTRACT

          The acquisition, delivery, and incorporation of metals into their respective metalloproteins are important cellular processes. These processes are tightly controlled in order to prevent exposure of cells to free-metal concentrations that could yield oxidative damage. Copper (Cu) is one such metal that is required as a cofactor in a variety of proteins. However, when present in excessive amounts, Cu is toxic due to its oxidative capability. Cytochrome c oxidases (Coxs) are among the metalloproteins whose assembly and activity require the presence of Cu in their catalytic subunits. In this study, we focused on the acquisition of Cu for incorporation into the heme-Cu binuclear center of the cbb 3-type Cox ( cbb 3-Cox) in the facultative phototroph Rhodobacter capsulatus. Genetic screens identified a cbb 3-Cox defective mutant that requires Cu 2+ supplementation to produce an active cbb 3-Cox. Complementation of this mutant using wild-type genomic libraries unveiled a novel gene ( ccoA) required for cbb 3-Cox biogenesis. In the absence of CcoA, the cellular Cu content decreases and cbb 3-Cox assembly and activity become defective. CcoA shows homology to major facilitator superfamily (MFS)-type transporter proteins. Members of this family are known to transport small solutes or drugs, but so far, no MFS protein has been implicated in cbb 3-Cox biogenesis. These findings provide novel insights into the maturation and assembly of membrane-integral metalloproteins and on a hitherto-unknown function(s) of MFS-type transporters in bacterial Cu acquisition.

          IMPORTANCE

          Biogenesis of energy-transducing membrane-integral enzymes, like the heme copper-containing cytochrome c oxidases, and the acquisition of transition metals, like copper, as their catalytic cofactors are vital processes for all cells. These widespread and well-controlled processes are poorly understood in all organisms, including bacteria. Defects in these processes lead to severe mitochondrial diseases in humans and poor crop yields in plants. In this study, using the facultative phototroph Rhodobacter capsulatus as a model organism, we report on the discovery of a novel major facilitator superfamily (MFS)-type transporter (CcoA) that affects cellular copper content and cbb 3-type cytochrome c oxidase production in bacteria.

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          Most cited references56

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          Major facilitator superfamily.

          The major facilitator superfamily (MFS) is one of the two largest families of membrane transporters found on Earth. It is present ubiquitously in bacteria, archaea, and eukarya and includes members that can function by solute uniport, solute/cation symport, solute/cation antiport and/or solute/solute antiport with inwardly and/or outwardly directed polarity. All homologous MFS protein sequences in the public databases as of January 1997 were identified on the basis of sequence similarity and shown to be homologous. Phylogenetic analyses revealed the occurrence of 17 distinct families within the MFS, each of which generally transports a single class of compounds. Compounds transported by MFS permeases include simple sugars, oligosaccharides, inositols, drugs, amino acids, nucleosides, organophosphate esters, Krebs cycle metabolites, and a large variety of organic and inorganic anions and cations. Protein members of some MFS families are found exclusively in bacteria or in eukaryotes, but others are found in bacteria, archaea, and eukaryotes. All permeases of the MFS possess either 12 or 14 putative or established transmembrane alpha-helical spanners, and evidence is presented substantiating the proposal that an internal tandem gene duplication event gave rise to a primordial MFS protein prior to divergence of the family members. All 17 families are shown to exhibit the common feature of a well-conserved motif present between transmembrane spanners 2 and 3. The analyses reported serve to characterize one of the largest and most diverse families of transport proteins found in living organisms.
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            Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis for the separation of proteins in the range from 1 to 100 kDa.

            A discontinuous sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) system for the separation of proteins in the range from 1 to 100 kDa is described. Tricine, used as the trailing ion, allows a resolution of small proteins at lower acrylamide concentrations than in glycine-SDS-PAGE systems. A superior resolution of proteins, especially in the range between 5 and 20 kDa, is achieved without the necessity to use urea. Proteins above 30 kDa are already destacked within the sample gel. Thus a smooth passage of these proteins from sample to separating gel is warranted and overloading effects are reduced. This is of special importance when large amounts of protein are to be loaded onto preparative gels. The omission of glycine and urea prevents disturbances which might occur in the course of subsequent amino acid sequencing.
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              TCDB: the Transporter Classification Database for membrane transport protein analyses and information

              The Transporter Classification Database (TCDB) is a web accessible, curated, relational database containing sequence, classification, structural, functional and evolutionary information about transport systems from a variety of living organisms. TCDB is a curated repository for factual information compiled from >10 000 references, encompassing ∼3000 representative transporters and putative transporters, classified into >400 families. The transporter classification (TC) system is an International Union of Biochemistry and Molecular Biology approved system of nomenclature for transport protein classification. TCDB is freely accessible at . The web interface provides several different methods for accessing the data, including step-by-step access to hierarchical classification, direct search by sequence or TC number and full-text searching. The functional ontology that underlies the database structure facilitates powerful query searches that yield valuable data in a quick and easy way. The TCDB website also offers several tools specifically designed for analyzing the unique characteristics of transport proteins. TCDB not only provides curated information and a tool for classifying newly identified membrane proteins, but also serves as a genome transporter-annotation tool.
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                Author and article information

                Journal
                mBio
                MBio
                mbio
                mbio
                mBio
                mBio
                American Society of Microbiology (1752 N St., N.W., Washington, DC )
                2150-7511
                31 January 2012
                Jan-Feb 2012
                : 3
                : 1
                : e00293-11
                Affiliations
                Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, USA, [ a ] and
                Institut für Biochemie und Molekularbiologie, ZMBZ, Albert Ludwig University of Freiburg, Freiburg, Germany [ b ]
                Author notes
                Address correspondence to Fevzi Daldal, fdaldal@ 123456sas.upenn.edu .

                *Present address: State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an, People’s Republic of China.

                Editor Howard Shuman, University of Chicago

                Article
                mBio00293-11
                10.1128/mBio.00293-11
                3266609
                22294680
                64528c7b-43ab-4419-a53d-519e6d92cf05
                Copyright © 2012 Ekici et al.

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 9 December 2011
                : 16 December 2011
                Page count
                Pages: 11
                Categories
                Research Article
                Custom metadata
                January/February 2012

                Life sciences
                Life sciences

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