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Biomolecules Jan 2021Cell plasma membrane proteins are considered as gatekeepers of the cell and play a major role in regulating various processes. Transport proteins constitute a subclass... (Review)
Review
Cell plasma membrane proteins are considered as gatekeepers of the cell and play a major role in regulating various processes. Transport proteins constitute a subclass of cell plasma membrane proteins enabling the exchange of molecules and ions between the extracellular environment and the cytosol. A plethora of human pathologies are associated with the altered expression or dysfunction of cell plasma membrane transport proteins, making them interesting therapeutic drug targets. However, the search for therapeutics is challenging, since many drug candidates targeting cell plasma membrane proteins fail in (pre)clinical testing due to inadequate selectivity, specificity, potency or stability. These latter characteristics are met by nanobodies, which potentially renders them eligible therapeutics targeting cell plasma membrane proteins. Therefore, a therapeutic nanobody-based strategy seems a valid approach to target and modulate the activity of cell plasma membrane transport proteins. This review paper focuses on methodologies to generate cell plasma membrane transport protein-targeting nanobodies, and the advantages and pitfalls while generating these small antibody-derivatives, and discusses several therapeutic nanobodies directed towards transmembrane proteins, including channels and pores, adenosine triphosphate-powered pumps and porters.
Topics: Antigens; Cell Membrane; Humans; Membrane Transport Proteins; Models, Biological; Single-Domain Antibodies
PubMed: 33418902
DOI: 10.3390/biom11010063 -
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 -
Current Opinion in Structural Biology Aug 2019The Golgi apparatus plays a central role in the secretory pathway as a hub for posttranslational modification, protein sorting and quality control. To date, there is... (Review)
Review
The Golgi apparatus plays a central role in the secretory pathway as a hub for posttranslational modification, protein sorting and quality control. To date, there is little structural or biochemical information concerning the function of transporters that reside within this organelle. The SLC35 family of nucleotide sugar transporters link the synthesis of activated sugar molecules and sulfate in the cytoplasm, with the luminal transferases that catalyse their attachment to proteins and lipids during glycosylation and sulfation. A recent crystal structure of the GDP-mannose transporter has revealed key sequence motifs that direct ligand recognition and transport. Further biochemical studies unexpectedly found a requirement for short chain lipids in activating the transporter, suggesting a possible route for transport regulation within the Golgi.
Topics: Animals; Golgi Apparatus; Humans; Membrane Transport Proteins; Nucleotides; Sugars
PubMed: 30999236
DOI: 10.1016/j.sbi.2019.03.019 -
Research in Microbiology 2018To understand antibiotic resistance in Gram-negative bacteria, a key point is to investigate antibiotic accumulation, which is defined by influx and efflux. Several... (Review)
Review
To understand antibiotic resistance in Gram-negative bacteria, a key point is to investigate antibiotic accumulation, which is defined by influx and efflux. Several methods exist to evaluate membrane permeability and efflux pump activity, but they present disadvantages and limitations. An optimized spectrofluorimetric method using intrinsic tryptophan fluorescence as an internal standard, as well as a complementary microfluorimetric assay following time-course accumulation in intact individual cells, have been developed. Comparing the latter population and single cell approaches can lead to an understanding of phenotypic heterogeneity within a population. The two methodologies lead to determination of parameters, concentration, accumulation rates and localization that contribute to emerging concepts (RTC2T, SICAR) with the aim of identifying and detailing antibiotic chemotypes involved in influx/efflux.
Topics: Anti-Bacterial Agents; Bacterial Proteins; Biological Transport; Fluorescence; Gram-Negative Bacteria; Membrane Transport Proteins; Multigene Family
PubMed: 29208490
DOI: 10.1016/j.resmic.2017.11.005 -
Biochimica Et Biophysica Acta Mar 2015The enzyme IIC (EIIC) component of the phosphotransferase system (PTS) is responsible for selectively transporting sugar molecules across the inner bacterial membrane.... (Review)
Review
BACKGROUND
The enzyme IIC (EIIC) component of the phosphotransferase system (PTS) is responsible for selectively transporting sugar molecules across the inner bacterial membrane. This is accomplished in parallel with phosphorylation of the sugar, which prevents efflux of the sugar back across the membrane. This process is a key part of an extensive signaling network that allows bacteria to efficiently utilize preferred carbohydrate sources.
SCOPE OF REVIEW
The goal of this review is to examine the current understanding of the structural features of the EIIC and how it mediates concentrative, selective sugar transport. The crystal structure of an N,N'-diacetylchitobiose transporter is used as a structural template for the glucose superfamily of PTS transporters.
MAJOR CONCLUSIONS
Comparison of protein sequences in context with the known EIIC structure suggests that members of the glucose superfamily of PTS transporters may exhibit variations in topology. Despite these differences, a conserved histidine and glutamate appear to have roles shared across the superfamily in sugar binding and phosphorylation. In the proposed transport model, a rigid body motion between two structural domains and movement of an intracellular loop provide the substrate binding site with alternating access, and reveal a surface required for interaction with the phosphotransfer protein responsible for catalysis.
GENERAL SIGNIFICANCE
The structural and functional data discussed here give a preliminary understanding of how transport in EIIC is achieved. However, given the great sequence diversity between varying glucose-superfamily PTS transporters and lack of data on conformational changes needed for transport, additional structures of other members and conformations are still required. This article is part of a Special Issue entitled: Structural biochemistry and biophysics of membrane proteins.
Topics: Amino Acid Sequence; Bacterial Proteins; Glucose; Membrane Transport Proteins; Models, Molecular; Molecular Sequence Data; Phosphorylation; Protein Binding; Protein Structure, Tertiary; Sequence Homology, Amino Acid
PubMed: 24657490
DOI: 10.1016/j.bbagen.2014.03.013 -
Research in Microbiology 2018The putative mechanism by which bacterial RND-type multidrug efflux pumps recognize and transport their substrates is a complex and fascinating enigma of structural... (Review)
Review
The putative mechanism by which bacterial RND-type multidrug efflux pumps recognize and transport their substrates is a complex and fascinating enigma of structural biology. How a single protein can recognize a huge number of unrelated compounds and transport them through one or just a few mechanisms is an amazing feature not yet completely unveiled. The appearance of cooperativity further complicates the understanding of structure-dynamics-activity relationships in these complex machineries. Experimental techniques may have limited access to the molecular determinants and to the energetics of key processes regulating the activity of these pumps. Computer simulations are a complementary approach that can help unveil these features and inspire new experiments. Here we review recent computational studies that addressed the various molecular processes regulating the activity of RND efflux pumps.
Topics: Anti-Bacterial Agents; Bacteria; Bacterial Proteins; Computer Simulation; Membrane Transport Proteins
PubMed: 29407044
DOI: 10.1016/j.resmic.2017.12.001 -
Biochimica Et Biophysica Acta Oct 2015
Topics: Antineoplastic Agents; Gene Expression Regulation, Neoplastic; Humans; Ion Channels; Membrane Transport Proteins; Neoplasms; Signal Transduction
PubMed: 26100062
DOI: 10.1016/j.bbamem.2015.06.017 -
Clinical Pharmacology and Therapeutics Nov 2016Membrane transport proteins have central physiological function in maintaining cerebral homeostasis. These transporters are expressed in almost all cerebral cells in... (Review)
Review
Membrane transport proteins have central physiological function in maintaining cerebral homeostasis. These transporters are expressed in almost all cerebral cells in which they regulate the movement of a wide range of solutes, including endogenous substrates, xenobiotic, and therapeutic drugs. Altered activity/expression of central nervous system (CNS) transporters has been implicated in the onset and progression of multiple neurological diseases. Neurological diseases are heterogeneous diseases that involve complex pathological alterations with only a few treatment options; therefore, there is a great need for the development of novel therapeutic treatments. To that end, transporters have emerged recently to be promising therapeutic targets to halt or slow the course of neurological diseases. The objective of this review is to discuss implications of transporters in neurological diseases and summarize available evidence for targeting transporters as decent therapeutic approach in the treatment of neurological diseases.
Topics: Animals; Humans; Membrane Transport Proteins; Models, Neurological; Molecular Targeted Therapy; Nervous System Diseases
PubMed: 27447939
DOI: 10.1002/cpt.435 -
Current Opinion in Microbiology Jun 2021All mechanisms of clinical antibiotic resistance benefit from activities of polyspecific efflux pumps acting to reduce intracellular accumulation of toxins and... (Review)
Review
All mechanisms of clinical antibiotic resistance benefit from activities of polyspecific efflux pumps acting to reduce intracellular accumulation of toxins and antibiotics. In Gram-negative bacteria, the major polyspecific efflux transporters belong to the Resistance-Nodulation-cell Division (RND) superfamily of proteins, which are capable of expelling thousands of structurally diverse compounds. Recent structural and functional advances generated novel insights into mechanisms underlying the biochemical versatility of RND transporters. This opinion article reviews these mechanisms and discusses implications of the polyspecificity of RND transporters for bacterial survival and for the development of efflux pump inhibitors effective in clinics.
Topics: Anti-Bacterial Agents; Bacterial Proteins; Biological Transport; Drug Resistance, Microbial; Drug Resistance, Multiple, Bacterial; Gram-Negative Bacteria; Membrane Transport Proteins
PubMed: 33940284
DOI: 10.1016/j.mib.2021.03.009 -
Molecular and Biochemical Parasitology Jan 2019Kinetoplastid parasites such as Trypanosoma brucei, Trypanosoma cruzi, and Leishmania species rely upon their insect and vertebrate hosts to provide a plethora of... (Review)
Review
Kinetoplastid parasites such as Trypanosoma brucei, Trypanosoma cruzi, and Leishmania species rely upon their insect and vertebrate hosts to provide a plethora of nutrients throughout their life cycles. Nutrients and ions critical for parasite survival are taken up across the parasite plasma membrane by transporters and channels, polytopic membrane proteins that provide substrate-specific pores across the hydrophobic barrier. However, transporters and channels serve a wide range of biological functions beyond uptake of nutrients. This article highlights the diversity of activities that these integral membrane proteins serve and underscores the emerging complexity of their functions.
Topics: Biological Transport; Leishmania; Membrane Proteins; Membrane Transport Proteins; Protozoan Proteins; Trypanosoma brucei brucei; Trypanosoma cruzi
PubMed: 30590069
DOI: 10.1016/j.molbiopara.2018.12.006