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Pharmacology & Therapeutics Oct 2015Nearly 30years ago, certain small, relatively nontoxic peptides were discovered to be capable of traversing the cell membrane. These cell-penetrating peptides, as they... (Review)
Review
Nearly 30years ago, certain small, relatively nontoxic peptides were discovered to be capable of traversing the cell membrane. These cell-penetrating peptides, as they are now called, have been shown to not only be capable of crossing the cell membrane themselves but can also carry many different therapeutic agents into cells, including small molecules, plasmid DNA, siRNA, therapeutic proteins, viruses, imaging agents, and other various nanoparticles. Many cell-penetrating peptides have been derived from natural proteins, but several other cell-penetrating peptides have been developed that are either chimeric or completely synthetic. How cell-penetrating peptides are internalized into cells has been a topic of debate, with some peptides seemingly entering cells through an endocytic mechanism and others by directly penetrating the cell membrane. Although the entry mechanism is still not entirely understood, it seems to be dependent on the peptide type, the peptide concentration, the cargo the peptide transports, and the cell type tested. With new intracellular disease targets being discovered, cell-penetrating peptides offer an exciting approach for delivering drugs to these intracellular targets. There are hundreds of cell-penetrating peptides being studied for drug delivery, and ongoing studies are demonstrating their success both in vitro and in vivo.
Topics: Biological Transport; Cell Membrane; Cell-Penetrating Peptides; Drug Delivery Systems; Enzymes; Humans; Nucleic Acids; Proteins
PubMed: 26210404
DOI: 10.1016/j.pharmthera.2015.07.003 -
Biochemistry and Cell Biology =... Dec 2016Cholesterol plays an important role in determining the biophysical properties of membranes in mammalian cells, and the concentration of cholesterol in membranes is... (Review)
Review
Cholesterol plays an important role in determining the biophysical properties of membranes in mammalian cells, and the concentration of cholesterol in membranes is tightly regulated. Cholesterol moves among membrane organelles by a combination of vesicular and nonvesicular transport pathways, but the details of these transport pathways are not well understood. In this review, we discuss the mechanisms for nonvesicular sterol transport with an emphasis on the role of STARD4, a small, soluble, cytoplasmic sterol transport protein. STARD4 can rapidly equilibrate sterol between membranes, especially membranes with anionic lipid headgroups. We also discuss the sterol transport in late endosomes and lysosomes, which is mediated by a soluble protein, NPC2, and a membrane protein, NPC1. Homozygous mutations in these proteins lead to a lysosomal lipid storage disorder, Niemann-Pick disease type C. Many of the disease-causing mutations in NPC1 are associated with degradation of the mutant NPC1 proteins in the endoplasmic reticulum. Several histone deacetylase inhibitors have been found to rescue the premature degradation of the mutant NPC1 proteins, and one of these is now in a small clinical trial.
Topics: Biological Transport; Carrier Proteins; Humans; Intracellular Signaling Peptides and Proteins; Membrane Glycoproteins; Membrane Transport Proteins; Niemann-Pick C1 Protein; Sterols
PubMed: 27421092
DOI: 10.1139/bcb-2015-0154 -
Amino Acids Aug 2022L-Carnosine (β-alanyl-L-histidine) is a well-known antioxidant and neuroprotector in various models on animals and cell cultures. However, while there is a plethora of...
L-Carnosine (β-alanyl-L-histidine) is a well-known antioxidant and neuroprotector in various models on animals and cell cultures. However, while there is a plethora of data demonstrating its efficiency as a neuroprotector, there is a distinct lack of data regarding the mechanism of its take up by neurons. According to literature, cultures of rat astrocytes, SKPT cells and rat choroid plexus epithelial cells take up carnosine via the H-coupled PEPT2 membrane transporter. We've assessed the effectiveness and mechanism of carnosine transport, and its stability in primary rat cortical culture neurons. We demonstrated that neurons take up carnosine via active transport with Km = 119 μM and a maximum velocity of 0.289 nmol/mg (prot)/min. Passive transport speed constituted 0.21∙10 nmol/mg (prot)/min (with 119 μM concentration in the medium)-significantly less than active transport speed. However, carnosine concentrations over 12.5 mM led to passive transport speed becoming greater than active transport speed. Using PEPT2 inhibitor zofenopril, we demonstrated that PEPT2-dependent transport is one of the main modes of carnosine take up by neurons. Our experiments demonstrated that incubation with carnosine does not affect PEPT2 amount present in culture. At the same time, after removing carnosine from the medium, its elimination speed by culture cells reached 0.035 nmol/mg (prot)/min, which led to a decrease in carnosine quantity to control levels in culture within 1 h. Thus, carnosine is taken up by neurons with an effectiveness comparable to that of other PEPT2 substrates, but its elimination rate suggests that for effective use as a neuroprotector it's necessary to either maintain a high concentration in brain tissue, or increase the effectiveness of glial cell synthesis of endogenous carnosine and its shuttling into neurons, or use more stable chemical modifications of carnosine.
Topics: Animals; Biological Transport, Active; Carnosine; Choroid Plexus; Membrane Transport Proteins; Rats; Symporters
PubMed: 34694500
DOI: 10.1007/s00726-021-03094-5 -
Biochemical Society Transactions Apr 2020Solute carrier (SLC) transporters play important roles in regulating the movement of small molecules and ions across cellular membranes. In mammals, they play an... (Review)
Review
Solute carrier (SLC) transporters play important roles in regulating the movement of small molecules and ions across cellular membranes. In mammals, they play an important role in regulating the uptake of nutrients and vitamins from the diet, and in controlling the distribution of their metabolic intermediates within the cell. Several SLC families also play an important role in drug transport and strategies are being developed to hijack SLC transporters to control and regulate drug transport within the body. Through the addition of amino acid and peptide moieties several novel antiviral and anticancer agents have been developed that hijack the proton-coupled oligopeptide transporters, PepT1 (SCL15A1) and PepT2 (SLC15A2), for improved intestinal absorption and renal retention in the body. A major goal is to understand the rationale behind these successes and expand the library of prodrug molecules that utilise SLC transporters. Recent co-crystal structures of prokaryotic homologues of the human PepT1 and PepT2 transporters have shed important new insights into the mechanism of prodrug recognition. Here, I will review recent developments in our understanding of ligand recognition and binding promiscuity within the SLC15 family, and discuss current models for prodrug recognition.
Topics: Animals; Biological Transport; Crystallography, X-Ray; Drug Design; Humans; Oligopeptides; Peptide Transporter 1; Prodrugs; Symporters; Valacyclovir; Valganciclovir
PubMed: 32219385
DOI: 10.1042/BST20180302 -
Methods in Molecular Biology (Clifton,... 2022Normal functions of cell-surface proteins are dependent on their proper trafficking from the site of synthesis to the cell surface. Transport proteins mediating solute...
Normal functions of cell-surface proteins are dependent on their proper trafficking from the site of synthesis to the cell surface. Transport proteins mediating solute transfer across the plasma membrane constitute an important group of cell-surface proteins. There are several diseases resulting from mutations in these proteins that interfere with their transport function or trafficking, depending on the impact of the mutations on protein folding and structure. Recent advances in successful treatment of some of these diseases with small molecules which correct the mutations-induced folding and structural changes underline the need for detailed structural and biophysical characterization of membrane proteins. This requires methods to express and purify these proteins using heterologous expression systems. Here, using the solute carrier (SLC) transporter NaCT (Na-coupled citrate transporter) as an example, we describe experimental strategies for this approach. We chose this example because several mutations in NaCT, distributed throughout the protein, cause a severe neurologic disease known as early infantile epileptic encephalopathy-25 (EIEE-25). NaCT was modified with various peptide tags, including a RGS-His, a Twin-Strep, the SUMOstar domain, and an enhanced green fluorescent protein (EGFP), each alone or in various combinations. When transiently expressed in HEK293 cells, recombinant NaCT proteins underwent complex glycosylation, compartmentalized with the plasma membrane, and exhibited citrate transport activity similar to the nontagged protein. Surface NaCT expression was enhanced by the presence of SUMOstar on the N-terminus. The dual-purpose peptide epitopes RGS-His and Twin-Strep facilitated detection of NaCT by immunohistochemistry and western blot and may serve useful tags for affinity purification. This approach sets the stage for future analyses of mutant NaCT proteins that may alter protein folding and trafficking. It also demonstrates the capability of a transient mammalian cell expression system to produce human NaCT of sufficient quality and quantity to augment future biophysical and structural studies and drug discovery efforts.
Topics: Animals; Biological Transport; Cell Membrane; HEK293 Cells; Humans; Mammals; Membrane Proteins; Mutant Proteins; Peptides; Symporters
PubMed: 35773591
DOI: 10.1007/978-1-0716-2368-8_18 -
Archives of Medical Research Nov 2014The blood-brain barrier (BBB) is a dynamic and complex interface between the blood and the central nervous system regulating brain homeostasis. Major functions of the... (Review)
Review
The blood-brain barrier (BBB) is a dynamic and complex interface between the blood and the central nervous system regulating brain homeostasis. Major functions of the BBB include the transport of nutrients and protection of the brain from toxic compounds. This review summarizes the most important transport pathways contributing to the nutrition of the brain. Carrier-mediated transport selectively delivers small molecules like sugars, amino acids, vitamins, and trace elements. Large biomolecules, lipoproteins, peptide and protein hormones cross the BBB by receptor-mediated transport. Active efflux transporters participate in the brain efflux of endogenous metabolites as well as toxins, xenobiotics and drugs. Dysfunction in the transport of nutrients at the BBB is described in several neurological disorders and diseases. The BBB penetration of neuroprotective nutrients, especially plant polyphenols and alkaloids, their potential protective effect on brain endothelium and the interaction of nutraceuticals with active efflux transporters at the BBB are discussed. In vitro BBB models to examine nutrient transport are also presented.
Topics: ATP-Binding Cassette Transporters; Biological Transport; Blood-Brain Barrier; Carrier Proteins; Humans; Lipid Metabolism; Neuroprotective Agents; Nutritional Status; Peptides; Toxins, Biological
PubMed: 25481827
DOI: 10.1016/j.arcmed.2014.11.018 -
Critical Reviews in Biochemistry and... Apr 2019Recognition of foreign and dysregulated antigens by the cellular innate and adaptive immune systems is in large part dependent on the cell surface display of peptide/MHC... (Review)
Review
Recognition of foreign and dysregulated antigens by the cellular innate and adaptive immune systems is in large part dependent on the cell surface display of peptide/MHC (pMHC) complexes. The formation of such complexes requires the generation of antigenic peptides, proper folding of MHC molecules, loading of peptides onto MHC molecules, glycosylation, and transport to the plasma membrane. This complex series of biosynthetic, biochemical, and cell biological reactions is known as "antigen processing and presentation". Here, we summarize recent work, focused on the structural and functional characterization of the key MHC-I-dedicated chaperones, tapasin, and TAPBPR. The mechanisms reflect the ability of conformationally flexible molecules to adapt to their ligands, and are comparable to similar processes that are exploited in peptide antigen loading in the MHC-II pathway.
Topics: Animals; Antigen Presentation; Antigen-Presenting Cells; Histocompatibility Antigens Class I; Histocompatibility Antigens Class II; Humans; Immunoglobulins; Membrane Proteins; Membrane Transport Proteins; Models, Molecular; Molecular Chaperones; Peptides; Protein Conformation
PubMed: 31084439
DOI: 10.1080/10409238.2019.1610352 -
Molecular Microbiology May 2020The twin-arginine protein transport (Tat pathway) is found in prokaryotes and plant organelles and transports folded proteins across membranes. Targeting of substrates... (Review)
Review
The twin-arginine protein transport (Tat pathway) is found in prokaryotes and plant organelles and transports folded proteins across membranes. Targeting of substrates to the Tat system is mediated by the presence of an N-terminal signal sequence containing a highly conserved twin-arginine motif. The Tat machinery comprises membrane proteins from the TatA and TatC families. Assembly of the Tat translocon is dynamic and is triggered by the interaction of a Tat substrate with the Tat receptor complex. This review will summarise recent advances in our understanding of Tat transport, focusing in particular on the roles played by Tat signal peptides in protein targeting and translocation.
Topics: Amino Acid Motifs; Bacterial Proteins; Cell Membrane; Escherichia coli Proteins; Membrane Transport Proteins; Protein Binding; Protein Conformation; Protein Sorting Signals; Protein Transport; Twin-Arginine-Translocation System
PubMed: 31971282
DOI: 10.1111/mmi.14461 -
Advances in Experimental Medicine and... 2019In recent years, a growing number of studies have implicated the coordinated action of NPC1 and NPC2 in intralysosomal transport and efflux of cholesterol. Our current... (Review)
Review
In recent years, a growing number of studies have implicated the coordinated action of NPC1 and NPC2 in intralysosomal transport and efflux of cholesterol. Our current understanding of this process developed with just over two decades of research. Since the cloning of the genes encoding the NPC1 and NPC2 proteins, studies of the biochemical defects observed when either gene is mutated along with computational and structural studies have unraveled key steps in the underlying mechanism. Here, we summarize the major contributions to our understanding of the proposed cholesterol transport controlled by NPC1 and NPC2, and briefly discuss recent findings of cholesterol binding and transport proteins beyond NPC1 and NPC2. We conclude with key questions and major challenges for future research on cholesterol transport by the NPC1 and NPC2 proteins.
Topics: Biological Transport; Carrier Proteins; Cholesterol; Glycoproteins; Humans; Intracellular Signaling Peptides and Proteins; Membrane Glycoproteins; Niemann-Pick C1 Protein; Vesicular Transport Proteins
PubMed: 31098815
DOI: 10.1007/978-3-030-14265-0_8 -
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