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Science Advances Aug 2021The SLC15 family of proton-coupled solute carriers PepT1 and PepT2 play a central role in human physiology as the principal route for acquiring and retaining dietary...
The SLC15 family of proton-coupled solute carriers PepT1 and PepT2 play a central role in human physiology as the principal route for acquiring and retaining dietary nitrogen. A remarkable feature of the SLC15 family is their extreme substrate promiscuity, which has enabled the targeting of these transporters for the improvement of oral bioavailability for several prodrug molecules. Although recent structural and biochemical studies on bacterial homologs have identified conserved sites of proton and peptide binding, the mechanism of peptide capture and ligand promiscuity remains unclear for mammalian family members. Here, we present the cryo-electron microscopy structure of the outward open conformation of the rat peptide transporter PepT2 in complex with an inhibitory nanobody. Our structure, combined with molecular dynamics simulations and biochemical and cell-based assays, establishes a framework for understanding peptide and prodrug recognition within this pharmaceutically important transporter family.
Topics: Animals; Cryoelectron Microscopy; Mammals; Membrane Transport Proteins; Peptide Transporter 1; Peptides; Prodrugs; Protons; Rats; Symporters
PubMed: 34433568
DOI: 10.1126/sciadv.abh3355 -
Biochimica Et Biophysica Acta.... Apr 2018The uptake of nutrients, including metals, amino acids and peptides are required for many biological processes. Pathogenic bacteria scavenge these essential nutrients... (Review)
Review
The uptake of nutrients, including metals, amino acids and peptides are required for many biological processes. Pathogenic bacteria scavenge these essential nutrients from microenvironments to survive within the host. Pathogens must utilize a myriad of mechanisms to acquire these essential nutrients from the host while mediating the effects of toxicity. Bacteria utilize several transport proteins, including ATP-binding cassette (ABC) transporters to import and expel substrates. ABC transporters, conserved across all organisms, are powered by the energy from ATP to move substrates across cellular membranes. In this review, we will focus on nutrient uptake, the role of ABC importers at the host-pathogen interface, and explore emerging therapies to combat pathogenesis. This article is part of a Special Issue entitled: Beyond the Structure-Function Horizon of Membrane Proteins edited by Ute Hellmich, Rupak Doshi and Benjamin McIlwain.
Topics: ATP-Binding Cassette Transporters; Bacteria; Bacterial Infections; Bacterial Proteins; Biological Transport; Host-Pathogen Interactions; Models, Molecular; Protein Conformation; Virulence
PubMed: 28847505
DOI: 10.1016/j.bbamem.2017.08.011 -
Comprehensive Physiology Mar 2018Mammalian members of the proton-coupled oligopeptide transporter family are integral membrane proteins that mediate the cellular uptake of di/tripeptides and... (Review)
Review
Mammalian members of the proton-coupled oligopeptide transporter family are integral membrane proteins that mediate the cellular uptake of di/tripeptides and peptide-like drugs and couple substrate translocation to the movement of H , with the transmembrane electrochemical proton gradient providing the driving force. Peptide transporters are responsible for the (re)absorption of dietary and/or bacterial di- and tripeptides in the intestine and kidney and maintaining homeostasis of neuropeptides in the brain. These proteins additionally contribute to absorption of a number of pharmacologically important compounds. In this overview article, we have provided updated information on the structure, function, expression, localization, and activities of PepT1 (SLC15A1), PepT2 (SLC15A2), PhT1 (SLC15A4), and PhT2 (SLC15A3). Peptide transporters, in particular, PepT1 are discussed as drug-delivery systems in addition to their implications in health and disease. Particular emphasis has been placed on the involvement of PepT1 in the physiopathology of the gastrointestinal tract, specifically, its role in inflammatory bowel diseases. © 2018 American Physiological Society. Compr Physiol 8:731-760, 2018.
Topics: Amino Acid Sequence; Animals; Biological Transport; Humans; Inflammatory Bowel Diseases; Membrane Transport Proteins; Peptide Transporter 1; Sequence Alignment; Symporters
PubMed: 29687900
DOI: 10.1002/cphy.c170032 -
The Protein Journal Aug 2019The twin-arginine protein translocation (Tat) system has been characterized in bacteria, archaea and the chloroplast thylakoidal membrane. This system is distinct from... (Review)
Review
The twin-arginine protein translocation (Tat) system has been characterized in bacteria, archaea and the chloroplast thylakoidal membrane. This system is distinct from other protein transport systems with respect to two key features. Firstly, it accepts cargo proteins with an N-terminal signal peptide that carries the canonical twin-arginine motif, which is essential for transport. Second, the Tat system only accepts and translocates fully folded cargo proteins across the respective membrane. Here, we review the core essential features of folded protein transport via the bacterial Tat system, using the three-component TatABC system of Escherichia coli and the two-component TatAC systems of Bacillus subtilis as the main examples. In particular, we address features of twin-arginine signal peptides, the essential Tat components and how they assemble into different complexes, mechanistic features and energetics of Tat-dependent protein translocation, cytoplasmic chaperoning of Tat cargo proteins, and the remarkable proofreading capabilities of the Tat system. In doing so, we present the current state of our understanding of Tat-dependent protein translocation across biological membranes, which may serve as a lead for future investigations.
Topics: Arginine; Bacillus subtilis; Cell Membrane; Escherichia coli; Escherichia coli Proteins; Membrane Transport Proteins; Protein Folding; Protein Sorting Signals; Protein Transport; SEC Translocation Channels; Twin-Arginine-Translocation System
PubMed: 31401776
DOI: 10.1007/s10930-019-09859-y -
Biochimica Et Biophysica Acta Mar 2015Cellular uptake of small peptides is an important physiological process mediated by the PTR family of proton-coupled peptide transporters. In bacteria peptides can be... (Review)
Review
BACKGROUND
Cellular uptake of small peptides is an important physiological process mediated by the PTR family of proton-coupled peptide transporters. In bacteria peptides can be used as a source of amino acids and nitrogen. Similarly in humans peptide transport is the principle route for the uptake and retention of dietary protein in the form of short di- and tri-peptides for cellular metabolism.
SCOPE OF THE REVIEW
Recent crystal structures of bacterial PTR family transporters, combined with biochemical studies of transport have revealed key molecular details underpinning ligand promiscuity and the mechanism of proton-coupled transport within the family.
MAJOR CONCLUSIONS
Pairs of salt bridge interactions between transmembrane helices work in tandem to orchestrate alternating access transport within the PTR family. Key roles for residues conserved between bacterial and eukaryotic homologues suggest a conserved mechanism of peptide recognition and transport that in some cases has been subtly modified in individual species.
GENERAL SIGNIFICANCE
Physiological studies on PepT1 and PepT2, the mammalian members of this family, have identified these transporters as being responsible for the uptake of many pharmaceutically important drug molecules, including antibiotics and antiviral medications and demonstrated their promiscuity can be used for improving the oral bioavailability of poorly absorbed compounds. The insights gained from recent structural studies combined with previous physiological and biochemical analyses are rapidly advancing our understanding of this medically important transporter superfamily. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.
Topics: Amino Acid Sequence; Bacterial Proteins; Biological Transport; Membrane Transport Proteins; Models, Molecular; Molecular Sequence Data; Oligopeptides; Protein Structure, Secondary; Protein Structure, Tertiary; Sequence Homology, Amino Acid
PubMed: 24859687
DOI: 10.1016/j.bbagen.2014.05.011 -
Current Opinion in Structural Biology Aug 2017The POT family of membrane transporters use the inwardly directed proton electrochemical gradient to drive the uptake of essential nutrients into the cell. Originally... (Review)
Review
The POT family of membrane transporters use the inwardly directed proton electrochemical gradient to drive the uptake of essential nutrients into the cell. Originally discovered in bacteria, members of the family have been found in all kingdoms of life except the archaea. A remarkable feature of the family is their diverse substrate promiscuity. Whereas in mammals and bacteria they are predominantly di- and tri-peptide transporters, in plants the family has diverged to recognize nitrate, plant defence compounds and hormones. This promiscuity has led to the development of peptide-based pro-drugs that use PepT1 and PepT2, the mammalian homologues, to improve oral drug delivery. Recent crystal structures from bacterial and plant members of the family have revealed conserved features of the ligand-binding site and provided insights into post-translational regulation. Here I review the current understanding of transport, ligand promiscuity and regulation within the POT family.
Topics: Animals; Disulfides; Humans; Membrane Transport Proteins; Peptides; Protein Transport; Protons
PubMed: 27865112
DOI: 10.1016/j.sbi.2016.10.018 -
American Journal of Physiology. Renal... Nov 2018The ability to detect and track single molecules presents the advantage of visualizing the complex behavior of transmembrane proteins with a time and space resolution... (Review)
Review
The ability to detect and track single molecules presents the advantage of visualizing the complex behavior of transmembrane proteins with a time and space resolution that would otherwise be lost with traditional labeling and biochemical techniques. Development of new imaging probes has provided a robust method to study their trafficking and surface dynamics. This mini-review focuses on the current technology available for single-molecule labeling of transmembrane proteins, their advantages, and limitations. We also discuss the application of these techniques to the study of renal transporter trafficking in light of recent research.
Topics: Animals; Expressed Sequence Tags; Humans; Kidney; Luminescent Proteins; Membrane Transport Proteins; Microscopy, Fluorescence; Protein Transport; Recombinant Proteins; Single Molecule Imaging; Single-Domain Antibodies
PubMed: 30043625
DOI: 10.1152/ajprenal.00082.2017 -
The AAPS Journal Dec 2005Transmembrane transport of endogenous as well as synthetic opioid peptides is a critical determinant of pharmacokinetics and biologic efficacy of these peptides. This... (Review)
Review
Transmembrane transport of endogenous as well as synthetic opioid peptides is a critical determinant of pharmacokinetics and biologic efficacy of these peptides. This transport process influences the distribution of opioid peptides across the blood-brain barrier and their elimination from the body. A multitude of transport systems that recognize opioid peptides as substrates have been characterized at the functional level, and these transport systems are expressed differentially at different sites in the body. Many of these transport systems have been identified at the molecular level. These include the H(+)-coupled peptide transporters PEPT1 and PEPT2, the adenosine triphosphate-dependent efflux transporters P-glycoprotein and multidrug resistance-related protein 2, and several members of the organic anion-transporting polypeptide gene family. There are however many additional transport systems that are known to transport opioid peptides but their molecular identities still remain unknown.
Topics: Amino Acid Sequence; Animals; Humans; Membrane Transport Proteins; Molecular Sequence Data; Opioid Peptides; Peptide Fragments
PubMed: 16594637
DOI: 10.1208/aapsj070482 -
Clinical Pharmacology and Therapeutics Jul 2013The International Transporter Consortium (ITC) has recently described seven transporters of particular relevance to drug development. Based on the second ITC transporter... (Review)
Review
The International Transporter Consortium (ITC) has recently described seven transporters of particular relevance to drug development. Based on the second ITC transporter workshop in 2012, we have identified additional transporters of emerging importance in pharmacokinetics, interference of drugs with transport of endogenous compounds, and drug-drug interactions (DDIs) in humans. The multidrug and toxin extrusion proteins (MATEs, gene symbol SLC47A) mediate excretion of organic cations into bile and urine. MATEs are important in renal DDIs. Multidrug resistance proteins (MRPs or ABCCs) are drug and conjugate efflux pumps, and impaired activity of MRP2 results in conjugated hyperbilirubinemia. The bile salt export pump (BSEP or ABCB11) prevents accumulation of toxic bile salt concentrations in hepatocytes, and BSEP inhibition or deficiency may cause cholestasis and liver injury. In addition, examples are presented on the roles of nucleoside and peptide transporters in drug targeting and disposition.
Topics: Biological Transport; Cooperative Behavior; Drug Discovery; Drug Interactions; Humans; Internationality; Membrane Transport Proteins; Pharmaceutical Preparations
PubMed: 23588305
DOI: 10.1038/clpt.2013.74 -
Traffic (Copenhagen, Denmark) Feb 2008The relict plastid, or apicoplast, of the malaria parasite Plasmodium falciparum is an essential organelle and a promising drug target. Most apicoplast proteins are... (Review)
Review
The relict plastid, or apicoplast, of the malaria parasite Plasmodium falciparum is an essential organelle and a promising drug target. Most apicoplast proteins are nuclear encoded and post-translationally targeted into the organelle using a bipartite N-terminal extension, consisting of a typical endomembrane signal peptide and a plant-like transit peptide. Apicoplast protein targeting commences through the parasite's secretory pathway. We review recent experimental evidence suggesting that the apicoplast resides in the mainstream endomembrane system proximal to the Golgi. Further, we explore possible mechanisms for translocation of nuclear-encoded apicoplast proteins across the four bounding membranes. Recent insights into the composition of the transit peptide and how it is cleaved and degraded after use are also examined. Characterization of apicoplast targeting has not only shed light on how this group of parasites mediate intracellular protein trafficking events but also it has helped identify new targets for therapeutics. The distinctive leader sequences of apicoplast proteins make them readily identifiable, allowing assembly of a virtual organelle metabolome from the genome. Such analysis has lead to the identification of several biochemical pathways that are absent from the human host and thus represent novel therapeutic targets for parasitic infection.
Topics: Animals; Intracellular Membranes; Membrane Transport Proteins; Models, Biological; Plasmodium falciparum; Plastids; Protein Sorting Signals; Protein Transport
PubMed: 17900270
DOI: 10.1111/j.1600-0854.2007.00660.x