This is a repository copy of Tripartite ATP-independent periplasmic (TRAP) transporters and tripartite tricarboxylate transporters (TTT): From uptake to pathogenicity. White Rose Research Online URL for this paper: https://eprints.whiterose.ac.uk/127518/ Version: Published Version Article: Rosa, Leonardo T., Bianconi, Matheus E., Thomas, Gavin Hugh orcid.org/0000-0002- 9763-1313 et al. (1 more author) (2018) Tripartite ATP-independent periplasmic (TRAP) transporters and tripartite tricarboxylate transporters (TTT): From uptake to pathogenicity. Frontiers in Microbiology. 33. ISSN 1664-302X https://doi.org/10.3389/fcimb.2018.00033 Reuse This article is distributed under the terms of the Creative Commons Attribution (CC BY) licence. This licence allows you to distribute, remix, tweak, and build upon the work, even commercially, as long as you credit the authors for the original work. More information and the full terms of the licence here: https://creativecommons.org/licenses/ Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ REVIEW published: 12 February 2018 doi: 10.3389/fcimb.2018.00033 Tripartite ATP-Independent Periplasmic (TRAP) Transporters and Tripartite Tricarboxylate Transporters (TTT): From Uptake to Pathogenicity Leonardo T. Rosa 1, Matheus E. Bianconi 2, Gavin H. Thomas 3 and David J. Kelly 1* 1 Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom, 2 Department of Animal and Plant Sciences, University of Sheffield, Sheffield, United Kingdom, 3 Department of Biology, University of York, York, United Kingdom The ability to efficiently scavenge nutrients in the host is essential for the viability of any pathogen. All catabolic pathways must begin with the transport of substrate from the environment through the cytoplasmic membrane, a role executed by membrane transporters. Although several classes of cytoplasmic membrane transporters are described, high-affinity uptake of substrates occurs through Solute Binding-Protein (SBP) dependent systems. Three families of SBP dependant transporters are known; the primary ATP-binding cassette (ABC) transporters, and the secondary Tripartite ATP-independent periplasmic (TRAP) transporters and Tripartite Tricarboxylate Edited by: Kalai Mathee, Transporters (TTT). Far less well understood than the ABC family, the TRAP transporters Florida International University, are found to be abundant among bacteria from marine environments, and the United States TTT transporters are the most abundant family of proteins in many species of Reviewed by: Todd Kitten, β-proteobacteria. In this review, recent knowledge about these families is covered, with Virginia Commonwealth University, emphasis on their physiological and structural mechanisms, relating to several examples United States of relevant uptake systems in pathogenicity and colonization, using the SiaPQM sialic Franz Narberhaus, Ruhr University Bochum, Germany acid uptake system from Haemophilus influenzae and the TctCBA citrate uptake system *Correspondence: of Salmonella typhimurium as the prototypes for the TRAP and TTT transporters, David J. Kelly respectively. High-throughput analysis of SBPs has recently expanded considerably the d.kelly@sheffield.ac.uk range of putative substrates known for TRAP transporters, while the repertoire for the TTT Received: 29 October 2017 family has yet to be fully explored but both types of systems most commonly transport Accepted: 25 January 2018 carboxylates. Specialized spectroscopic techniques and site-directed mutagenesis have Published: 12 February 2018 enriched our knowledge of the way TRAP binding proteins capture their substrate, Citation: while structural comparisons show conserved regions for substrate coordination in Rosa LT, Bianconi ME, Thomas GH and Kelly DJ (2018) Tripartite both families. Genomic and protein sequence analyses show TTT SBP genes are ATP-Independent Periplasmic (TRAP) strikingly overrepresented in some bacteria, especially in the β-proteobacteria and some Transporters and Tripartite Tricarboxylate Transporters (TTT): α-proteobacteria. The reasons for this are not clear but might be related to a role for From Uptake to Pathogenicity. these proteins in signaling rather than transport. Front. Cell. Infect. Microbiol. 8:33. doi: 10.3389/fcimb.2018.00033 Keywords: solute transport, periplasmic binding-proteins, secondary transporter, high-affinity, carboxylic acids Frontiers in Cellular and Infection Microbiology | www.frontiersin.org 1 February 2018 | Volume 8 | Article 33 Rosa et al. Secondary SBP-Dependent Transporters in Pathogenicity SOLUTE BINDING-PROTEIN (SBP) related clusters has been proposed, based on their secondary DEPENDANT SECONDARY and tertiary structural patterns and their substrate specificities, TRANSPORTERS: THE TRAP AND TTT with the first classification into three distinct types proposed by Fukami-Kobayashi et al. (1999). With the exponential increase in SYSTEMS new entries for SBPs in genomic databases due to new sequencing capabilities, it became clear that the separation into three types Solute Binding-Protein (SBP) dependent transport systems was too simplistic to comprise SBP diversity, and thus a new contain, in addition to the membrane proteins, a soluble extra- model was presented by Berntsson et al. (2010) and recently cytoplasmic protein, located either free in the periplasm or revised by Scheepers et al. (2016). Both TRAP and TTT SBP‘s anchored to the membrane in the case of Gram-positive bacteria, are contained within the Type II group in the first classification, which binds the substrate with high affinity, and specificity, and inside Cluster E in the latter. This review summarizes the allowing uptake even in very low concentrations of ligands. Three evidence of a relationship between these two classes of secondary families of SBP dependant transporters are currently known, the high-affinity uptake systems and pathogenicity. Additionally, it composition of which are summarized in Figure 1. ATP-binding adds an evolutionary perspective regarding the expansion of the cassette (ABC) transporters use the free energy of ATP binding TTT family in some pathogens. and hydrolysis to move substrates across the membrane against a concentration gradient. First described in the early 1970‘s (Kalckar, 1971; Willis and Furlong, 1974), this family is by far THE TRAP TRANSPORTER FAMILY the best investigated SBP-dependant transporter family, with the maltose and vitamin B12 uptake systems as the most thoroughly The first characterization and naming of TRAP transporters studied models, and was subject of several reviews over recent was described in Rhodobacter capsulatus by Forward et al. years (Jones and George, 2004; Davidson et al., 2008; Rice et al., (1997), when a SBP encoding gene was found adjacent to two 2014; Maqbool et al., 2015; Wilkens, 2015; Locher, 2016). genes encoding transmembrane proteins of 12 (DctM) and 4 The Tripartite ATP-independent periplasmic (TRAP) (DctQ) predicted helices. Functional studies showed symport transporters (TC: 2.A.56) and Tripartite Tricarboxylate of C4-dicarboxylic acids apparently energized by the proton Transporters (TTT, TC: 2.A.80), on the other hand, use ion- motive-force. Subsequent studies showed that these systems can electrochemical gradients to move substrates in a symporter transport a variety of substrates under different contexts. Detailed mechanism, thus being defined as secondary transporters. These reviews about this family were provided by Kelly and Thomas two families are significantly less well-understood than ABC (2001) and Mulligan et al. (2011), and the following sections will systems but share a similar overall protein composition and focus on more recent insights. topology, as well as genomic organization. In addition to the SBP‘s (“P” subunit in TRAP systems, “C” subunit in TTT), Substrate Diversity of the TRAP Family and each system is comprised of two transmembrane proteins, Roles in Pathogenicity one well-conserved 12 transmembrane (TM) domain protein The best studied TRAP system is undoubtedly SiaPQM from (“M” subunit in the TRAP systems, “A” subunit in TTT) and Haemophilus influenzae (Figures 1, 2A), discovered by Severi one poorly conserved 4 TM domain protein (“Q” subunit in et al. (2005) to be involved in the uptake of sialic acid. Sialic TRAP systems, “B” subunit in the TTT) (Forward et al., 1997; acid is a generic name for a class of 9-carbon sugar acids used Winnen et al., 2003; Thomas et al., 2006; Hosaka et al., 2013, by most eukaryotic cells in the form of cell surface glycoproteins. Figure 1). However, no sequence similarity is found between For this reason, many pathogens evolved to mimic these surface the corresponding proteins in these families, thus representing structures in their own cell envelope, constituting an important either a case of convergent evolution (Fischer et al., 2010) or very virulence factor which improves evasion of the human immune ancient orthology and divergence (Winnen et al., 2003). system (Bouchet et al., 2003). In H. influenzae, absence of Regardless of their lack of sequence similarity, the SBPs from SiaPQM causes loss of sialic acid uptake and lack of incorporation these two families show very similar tertiary structures. They are in the lipo-oligossacharide (Allen et al., 2005), and a subsequent