The Concise Guide to PHARMACOLOGY 2023/24: Transporters

\ua9 2023 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of The British Pharmacological Society.The Concise Guide to PHARMACOLOGY 2023/24 is the sixth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of approximately 1800 drug targets, and over 6000 interactions with about 3900 ligands. There is an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (https://www.guidetopharmacology.org/), which provides more detailed views of target and ligand properties. Although the Concise Guide constitutes almost 500 pages, the material presented is substantially reduced compared to information and links presented on the website. It provides a permanent, citable, point-in-time record that will survive database updates. The full contents of this section can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.16182. Transporters are one of the six major pharmacological targets into which the Guide is divided, with the others being: G protein-coupled receptors, ion channels, nuclear hormone receptors, catalytic receptors and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The landscape format of the Concise Guide is designed to facilitate comparison of related targets from material contemporary to mid-2023, and supersedes data presented in the 2021/22, 2019/20, 2017/18, 2015/16 and 2013/14 Concise Guides and previous Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC-IUPHAR), therefore, providing official IUPHAR classification and nomenclature for human drug targets, where appropriate

The Concise Guide to PHARMACOLOGY 2023/24:Transporters

The Concise Guide to PHARMACOLOGY 2023/24 is the sixth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of approximately 1800 drug targets, and over 6000 interactions with about 3900 ligands. There is an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (https://www.guidetopharmacology.org/), which provides more detailed views of target and ligand properties. Although the Concise Guide constitutes almost 500 pages, the material presented is substantially reduced compared to information and links presented on the website. It provides a permanent, citable, point-in-time record that will survive database updates. The full contents of this section can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.16182. Transporters are one of the six major pharmacological targets into which the Guide is divided, with the others being: G protein-coupled receptors, ion channels, nuclear hormone receptors, catalytic receptors and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The landscape format of the Concise Guide is designed to facilitate comparison of related targets from material contemporary to mid-2023, and supersedes data presented in the 2021/22, 2019/20, 2017/18, 2015/16 and 2013/14 Concise Guides and previous Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC-IUPHAR), therefore, providing official IUPHAR classification and nomenclature for human drug targets, where appropriate.</p

The transport mechanism of the mitochondrial ADP/ATP carrier

The mitochondrial ADP/ATP carrier imports ADP from the cytosol and exports ATP from the mitochondrial matrix, which are key transport steps for oxidative phosphorylation in eukaryotic organisms. The transport protein belongs to the mitochondrial carrier family, a large transporter family in the inner membrane of mitochondria. It is one of the best studied members of the family and serves as a paradigm for the molecular mechanism of mitochondrial carriers. Structurally, the carrier consists of three homologous domains, each composed of two transmembrane α-helices linked with a loop and short α-helix on the matrix side. The transporter cycles between a cytoplasmic and matrix state in which a central substrate binding site is alternately accessible to these compartments for binding of ADP or ATP. On both the cytoplasmic and matrix side of the carrier are networks consisting of three salt bridges each. In the cytoplasmic state, the matrix salt bridge network is formed and the cytoplasmic network is disrupted, opening the central substrate binding site to the intermembrane space and cytosol, whereas the converse occurs in the matrix state. In the transport cycle, tighter substrate binding in the intermediate states allows the interconversion of conformations by lowering the energy barrier for disruption and formation of these networks, opening and closing the carrier to either side of the membrane in an alternating way. Conversion between cytoplasmic and matrix states might require the simultaneous rotation of three domains around a central translocation pathway, constituting a unique mechanism among transport proteins. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou

Fluoxetine (Prozac) Binding to Serotonin Transporter Is Modulated by Chloride and Conformational Changes

Serotonin transporter (SERT) is the main target for widely used antidepressant agents. Several of these drugs, including imipramine, citalopram, sertraline, and fluoxetine (Prozac), bound more avidly to SERT in the presence of Cl−. In contrast, Cl− did not enhance cocaine or paroxetine binding. A Cl− binding site recently identified in SERT, and shown to be important for Cl− dependent transport, was also critical for the Cl− dependence of antidepressant affinity. Mutation of the residues contributing to this site eliminated the Cl−-mediated affinity increase for imipramine and fluoxetine. Analysis of ligand docking to a single state of SERT indicated only small differences in the energy of interaction between bound ligands and Cl−. These differences in interaction energy cannot account for the affinity differences observed for Cl− dependence. However, fluoxetine binding led to a conformational change, detected by cysteine accessibility experiments, that was qualitatively different from that induced by cocaine or other ligands. Given the known Cl− requirement for serotonin-induced conformational changes, we propose that Cl− binding facilitates conformational changes required for optimal binding of fluoxetine and other antidepressant drugs

Reconstructing a Chloride-binding Site in a Bacterial Neurotransmitter Transporter Homologue

In ion-coupled transport proteins, occupation of selective ion-binding sites is required to trigger conformational changes that lead to substrate translocation. Neurotransmitter transporters, targets of abused and therapeutic drugs, require Na+ and Cl− for function. We recently proposed a chloride-binding site in these proteins not present in Cl−-independent prokaryotic homologues. Here we describe conversion of the Cl−-independent prokaryotic tryptophan transporter TnaT to a fully functional Cl−-dependent form by a single point mutation, D268S. Mutations in TnaT-D268S, in wild type TnaT and in serotonin transporter provide direct evidence for the involvement of each of the proposed residues in Cl− coordination. In both SERT and TnaT-D268S, Cl− and Na+ mutually increased each other's potency, consistent with electrostatic interaction through adjacent binding sites. These studies establish the site where Cl− binds to trigger conformational change during neurotransmitter transport

The recombinant subdomain IIIB of human serum albumin displays activity of gonadotrophin surge-attenuating factor

BACKGROUND: Gonadotrophin surge-attenuating factor (GnSAF) is an as yet unidentified ovarian factor that acts on the pituitary to attenuate the pre-ovulatory LH surge. In a previous study, GnSAF bioactivity was proposed to derive, at least in part, from a C-terminal domain (95peptide) of human serum albumin (HSA). METHODS AND RESULTS: We employ here the expression-secretion system of Pichia pastoris to produce and assay selected recombinant polypeptides of HSA for GnSAF activity. We show that the C-terminal 95peptide of HSA (residues 490-585; subdomain IIIB) can be expressed from P.pastoris in secreted form and supernatants from clones expressing this polypeptide reduce the GnRH-induced LH secretion of primary rat pituitary cultures by 50-82%. When expressed in the same system, HSA domain III (residues 381-585) or full-length HSA (residues 1-585) are inactive. The bioactive subdomain IIIB is also separable from either domain III or full-length HSA on Blue Sepharose chromatography. CONCLUSIONS: Taken together, the findings highlight the putative importance of HSA subdomain IIIB as a GnSAF-bioactive entity and introduce a unique experimental tool to engineer this molecule for structure-function analysis

The molecular mechanism of substrate binding and transport of the mitochondrial ADP/ATP carrier

Mitochondrial ADP/ATP carriers provide key transport steps in eukaryotic oxidative phosphorylation by importing ADP into the mitochondrial matrix and by exporting syn- thesized ATP to fuel cellular processes. Structures of the in- hibited cytoplasmic- and matrix-open states have confirmed an alternating access mechanism, but the molecular nature of substrate binding is unresolved. Here, we investigate all solvent-exposed residues in the translocation pathway in both conformational states of the mitochondrial ADP/ATP carrier. By combining binding studies with functional assays using single alanine replacement variants, we identify a single substrate binding site in the center of the cavity. It consists of three positively charged residues, which could bind the phosphate groups, and a cluster of three aliphatic and one aromatic residue, which could bind the adenosine moiety of M the nucleotides. In addition, two arginine/asparagine pairs are identified, which are unique to ADP/ATP carriers but play a role in binding. Importantly, the same residues are O involved in binding of both ADP and ATP, implying that the import and export steps occur consecutively and in a N reversible way. The features of the identified binding site explain the electrogenic nature of transport

Substrate binding in the mitochondrial ADP/ATP carrier is a step-wise process guiding the structural changes in the transport cycle.

Mitochondrial ADP/ATP carriers import ADP into the mitochondrial matrix and export ATP to the cytosol to fuel cellular processes. Structures of the inhibited cytoplasmic- and matrix-open states have confirmed an alternating access transport mechanism, but the molecular details of substrate binding remain unresolved. Here, we evaluate the role of the solvent-exposed residues of the translocation pathway in the process of substrate binding. We identify the main binding site, comprising three positively charged and a set of aliphatic and aromatic residues, which bind ADP and ATP in both states. Additionally, there are two pairs of asparagine/arginine residues on opposite sides of this site that are involved in substrate binding in a state-dependent manner. Thus, the substrates are directed through a series of binding poses, inducing the conformational changes of the carrier that lead to their translocation. The properties of this site explain the electrogenic and reversible nature of adenine nucleotide transport

A Single Cysteine Residue in the Translocation Pathway of the Mitosomal ADP/ATP Carrier from Cryptosporidium parvum Confers a Broad Nucleotide Specificity.

Cryptosporidiumparvum is a clinically important eukaryotic parasite that causes the disease cryptosporidiosis, which manifests with gastroenteritis-like symptoms. The protist has mitosomes, which are organelles of mitochondrial origin that have only been partially characterized. The genome encodes a highly reduced set of transport proteins of the SLC25 mitochondrial carrier family of unknown function. Here, we have studied the transport properties of one member of the C. parvum carrier family, demonstrating that it resembles the mitochondrial ADP/ATP carrier of eukaryotes. However, this carrier has a broader substrate specificity for nucleotides, transporting adenosine, thymidine, and uridine di- and triphosphates in contrast to its mitochondrial orthologues, which have a strict substrate specificity for ADP and ATP. Inspection of the putative translocation pathway highlights a cysteine residue, which is a serine in mitochondrial ADP/ATP carriers. When the serine residue is replaced by cysteine or larger hydrophobic residues in the yeast mitochondrial ADP/ATP carrier, the substrate specificity becomes broad, showing that this residue is important for nucleotide base selectivity in ADP/ATP carriers