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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 -
American Journal of Physiology. Cell... Jun 2022Sarcolemmal/plasmalemmal ATP-sensitive K (K) channels have key roles in many cell types and tissues. Hundreds of studies have described how the K channel activity and... (Review)
Review
Sarcolemmal/plasmalemmal ATP-sensitive K (K) channels have key roles in many cell types and tissues. Hundreds of studies have described how the K channel activity and ATP sensitivity can be regulated by changes in the cellular metabolic state, by receptor signaling pathways and by pharmacological interventions. These alterations in channel activity directly translate to alterations in cell or tissue function, that can range from modulating secretory responses, such as insulin release from pancreatic β-cells or neurotransmitters from neurons, to modulating contractile behavior of smooth muscle or cardiac cells to elicit alterations in blood flow or cardiac contractility. It is increasingly becoming apparent, however, that K channels are regulated beyond changes in their activity. Recent studies have highlighted that K channel surface expression is a tightly regulated process with similar implications in health and disease. The surface expression of K channels is finely balanced by several trafficking steps including synthesis, assembly, anterograde trafficking, membrane anchoring, endocytosis, endocytic recycling, and degradation. This review aims to summarize the physiological and pathophysiological implications of K channel trafficking and mechanisms that regulate K channel trafficking. A better understanding of this topic has potential to identify new approaches to develop therapeutically useful drugs to treat K channel-related diseases.
Topics: Adenosine Triphosphate; Biological Transport; Insulin; Insulin-Secreting Cells; KATP Channels; Protein Transport
PubMed: 35508187
DOI: 10.1152/ajpcell.00099.2022 -
Current Opinion in Plant Biology Aug 2022The nitrate and peptide transporter family (NPF) is one of the largest transporter families in the plant kingdom. The name of the family reflects the substrates (nitrate... (Review)
Review
The nitrate and peptide transporter family (NPF) is one of the largest transporter families in the plant kingdom. The name of the family reflects the substrates (nitrate and peptides) identified for the two founding members CHL1 and PTR2 from Arabidopsis thaliana almost 30 years ago. However, since then, the NPF has emerged as a hotspot for transporters with a wide range of crucial roles in plant specialized metabolism. Recent prominent examples include 1) controlling accumulation of antinutritional glucosinolates in Brassica seeds, 2) deposition of heat-stress tolerance flavonol diglucosides to pollen coats 3) production of anti-cancerous monoterpene indole alkaloid precursors in Catharanthus roseus and 4) detoxification of steroid glycoalkaloids in ripening tomatoes. In this review, we turn the spotlight on the emerging role of the NPF in plant specialized metabolism and its potential for improving crop traits through transport engineering.
Topics: Anion Transport Proteins; Arabidopsis; Gene Expression Regulation, Plant; Membrane Transport Proteins; Nitrates; Peptides; Plant Proteins; Plants
PubMed: 35709542
DOI: 10.1016/j.pbi.2022.102243 -
American Journal of Physiology. Renal... Dec 2022Kidney function is regulated by the circadian clock. Not only do glomerular filtration rate and urinary excretion oscillate during the day, but the expressions of...
Kidney function is regulated by the circadian clock. Not only do glomerular filtration rate and urinary excretion oscillate during the day, but the expressions of several renal transporter proteins also exhibit circadian rhythms. Interestingly, the circadian regulation of these transporters appears to be sexually dimorphic. Thus, the goal of the present study was to investigate the mechanisms by which the kidney function of the mouse is modulated by sex and time of day. To accomplish this, we developed the first computational models of epithelial water and solute transport along the mouse nephrons that represent the effects of sex and the circadian clock on renal hemodynamics and transporter activity. We conducted simulations to study how the circadian control of renal transport genes affects overall kidney function and how that process differs between male and female mice. Simulation results predicted that tubular transport differs substantially among segments, with relative variations in water and Na reabsorption along the proximal tubules and thick ascending limb tracking that of glomerular filtration rate. In contrast, relative variations in distal segment transport were much larger, with Na reabsorption almost doubling during the active phase. Oscillations in Na transport drive K transport variations in the opposite direction. Model simulations of basic helix-loop-helix ARNT like 1 (BMAL1) knockout mice predicted a significant reduction in net Na reabsorption along the distal segments in both sexes, but more so in males than in females. This can be attributed to the reduction of mean epithelial Na channel activity in males only, a sex-specific effect that may lead to a reduction in blood pressure in BMAL1-null males. How does the circadian control of renal transport genes affect overall kidney function, and how does that process differ between male and female mice? How does the differential circadian regulation of the expression levels of key transporter genes impact the transport processes along different nephron segments during the day? And how do those effects differ between males and females? We built computational models of mouse kidney function to answer these questions.
Topics: Mice; Female; Male; Animals; Sex Characteristics; ARNTL Transcription Factors; Nephrons; Sodium; Circadian Rhythm; Kidney; Membrane Transport Proteins; Water
PubMed: 36264883
DOI: 10.1152/ajprenal.00227.2022 -
International Journal of Molecular... Aug 2022Cell-penetrating peptides (CPPs) have been discovered to deliver chemical drugs, nucleic acids, and macromolecules to permeate cell membranes, creating a novel route for... (Review)
Review
Cell-penetrating peptides (CPPs) have been discovered to deliver chemical drugs, nucleic acids, and macromolecules to permeate cell membranes, creating a novel route for exogenous substances to enter cells. Up until now, various sequence structures and fundamental action mechanisms of CPPs have been established. Among them, arginine-rich peptides with unique cell penetration properties have attracted substantial scientific attention. Due to the positively charged essential amino acids of the arginine-rich peptides, they can interact with negatively charged drug molecules and cell membranes through non-covalent interaction, including electrostatic interactions. Significantly, the sequence design and the penetrating mechanisms are critical. In this brief synopsis, we summarize the transmembrane processes and mechanisms of arginine-rich peptides; and outline the relationship between the function of arginine-rich peptides and the number of arginine residues, arginine optical isomers, primary sequence, secondary and ternary structures, etc. Taking advantage of the penetration ability, biomedical applications of arginine-rich peptides have been refreshed, including drug/RNA delivery systems, biosensors, and blood-brain barrier (BBB) penetration. Understanding the membrane internalization mechanisms and design strategies of CPPs will expand their potential applications in clinical trials.
Topics: Arginine; Biological Transport; Cell Membrane; Cell-Penetrating Peptides; Drug Delivery Systems
PubMed: 36012300
DOI: 10.3390/ijms23169038 -
Proceedings of the National Academy of... Mar 2023Lysosomes are catabolic organelles involved in macromolecular digestion, and their dysfunction is associated with pathologies ranging from lysosomal storage disorders to...
Lysosomes are catabolic organelles involved in macromolecular digestion, and their dysfunction is associated with pathologies ranging from lysosomal storage disorders to common neurodegenerative diseases, many of which have lipid accumulation phenotypes. The mechanism of lipid efflux from lysosomes is well understood for cholesterol, while the export of other lipids, particularly sphingosine, is less well studied. To overcome this knowledge gap, we have developed functionalized sphingosine and cholesterol probes that allow us to follow their metabolism, protein interactions, and their subcellular localization. These probes feature a modified cage group for lysosomal targeting and controlled release of the active lipids with high temporal precision. An additional photocrosslinkable group allowed for the discovery of lysosomal interactors for both sphingosine and cholesterol. In this way, we found that two lysosomal cholesterol transporters, NPC1 and to a lesser extent LIMP-2/SCARB2, bind to sphingosine and showed that their absence leads to lysosomal sphingosine accumulation which hints at a sphingosine transport role of both proteins. Furthermore, artificial elevation of lysosomal sphingosine levels impaired cholesterol efflux, consistent with sphingosine and cholesterol sharing a common export mechanism.
Topics: Carrier Proteins; Sphingosine; Sterols; Intracellular Signaling Peptides and Proteins; Membrane Glycoproteins; Niemann-Pick C1 Protein; Cholesterol; Membrane Transport Proteins; Lysosomes
PubMed: 36893262
DOI: 10.1073/pnas.2213886120 -
Journal of Cellular and Molecular... Apr 2024Netrins, a family of secreted and membrane-associated proteins, can regulate axonal guidance, morphogenesis, angiogenesis, cell migration, cell survival, and... (Review)
Review
Netrins, a family of secreted and membrane-associated proteins, can regulate axonal guidance, morphogenesis, angiogenesis, cell migration, cell survival, and tumorigenesis. Four secreted netrins (netrin 1, 3, 4 and 5) and two glycosylphosphatidylinositols-anchored membrane proteins, netrin-G1 and G2, have been identified in mammals. Netrins and their receptors can serve as a biomarker and molecular therapeutic target for pathological differentiation, diagnosis and prognosis of malignant cancers. We review here the potential roles of the netrins family and their receptors in cancer.
Topics: Animals; Neoplasms; Netrins; Biological Transport; Carcinogenesis; Cell Differentiation; Membrane Proteins; Mammals
PubMed: 38546656
DOI: 10.1111/jcmm.18241 -
Oncogene Aug 2023Cancer cells are dependent on cholesterol, and they possess strictly controlled cholesterol homeostasis mechanisms. These allow them to smoothly switch between...
Cancer cells are dependent on cholesterol, and they possess strictly controlled cholesterol homeostasis mechanisms. These allow them to smoothly switch between cholesterol synthesis and uptake to fulfill their needs and to adapt environmental changes. Here we describe a mechanism of how cancer cells employ oncogenic growth factor signaling to promote uptake and utilization of extracellular cholesterol via Myeloid Zinc Finger 1 (MZF1)-mediated Niemann Pick C1 (NPC1) expression and upregulated macropinocytosis. Expression of p95ErbB2, highly oncogenic, standard-treatment resistant form of ErbB2 mobilizes lysosomes and activates EGFR, invasion and macropinocytosis. This is connected to a metabolic shift from cholesterol synthesis to uptake due to macropinocytosis-enabled flow of extracellular cholesterol. NPC1 increase facilitates extracellular cholesterol uptake and is necessary for the invasion of ErbB2 expressing breast cancer spheroids and ovarian cancer organoids, indicating a regulatory role for NPC1 in the process. The ability to obtain cholesterol as a byproduct of increased macropinocytosis allows cancer cells to direct the resources needed for the energy-consuming cholesterol synthesis towards other activities such as invasion. These results demonstrate that macropinocytosis is not only an alternative energy source for cancer cells but also an efficient way to provide building material, such as cholesterol, for its macromolecules and membranes.
Topics: Humans; Intracellular Signaling Peptides and Proteins; Cholesterol; Biological Transport; Niemann-Pick C1 Protein
PubMed: 37420029
DOI: 10.1038/s41388-023-02771-x -
Nature Communications Jan 2020Niemann-Pick C1 (NPC1), a lysosomal protein of 13 transmembrane helices (TMs) and three lumenal domains, exports low-density-lipoprotein (LDL)-derived cholesterol from...
Niemann-Pick C1 (NPC1), a lysosomal protein of 13 transmembrane helices (TMs) and three lumenal domains, exports low-density-lipoprotein (LDL)-derived cholesterol from lysosomes. TMs 3-7 of NPC1 comprise the Sterol-Sensing Domain (SSD). Previous studies suggest that mutation of the NPC1-SSD or the addition of the anti-fungal drug itraconazole abolishes NPC1 activity in cells. However, the itraconazole binding site and the mechanism of NPC1-mediated cholesterol transport remain unknown. Here, we report a cryo-EM structure of human NPC1 bound to itraconazole, which reveals how this binding site in the center of NPC1 blocks a putative lumenal tunnel linked to the SSD. Functional assays confirm that blocking this tunnel abolishes NPC1-mediated cholesterol egress. Intriguingly, the palmitate anchor of Hedgehog occupies a similar site in the homologous tunnel of Patched, suggesting a conserved mechanism for sterol transport in this family of proteins and establishing a central function of their SSDs.
Topics: Animals; Antifungal Agents; Binding Sites; Biological Transport; CHO Cells; Cell Line; Cholesterol; Cricetinae; Cricetulus; Cryoelectron Microscopy; HEK293 Cells; Humans; Intracellular Signaling Peptides and Proteins; Itraconazole; Niemann-Pick C1 Protein; Patched-1 Receptor; Protein Domains
PubMed: 31919352
DOI: 10.1038/s41467-019-13917-5 -
Proceedings of the National Academy of... Oct 2023Bacteria produce a structural layer of peptidoglycan (PG) that enforces cell shape, resists turgor pressure, and protects the cell. As bacteria grow and divide, the...
Bacteria produce a structural layer of peptidoglycan (PG) that enforces cell shape, resists turgor pressure, and protects the cell. As bacteria grow and divide, the existing layer of PG is remodeled and PG fragments are released. Enterics such as go to great lengths to internalize and reutilize PG fragments. is estimated to break down one-third of its cell wall, yet only loses ~0 to 5% of meso-diaminopimelic acid, a PG-specific amino acid, per generation. Two transporters were identified early on to possibly be the primary permease that facilitates PG fragment recycling, i) AmpG and ii) the Opp ATP binding cassette transporter in conjunction with a PG-specific periplasmic binding protein, MppA. The contribution of each transporter to PG recycling has been debated. Here, we have found that AmpG and MppA/Opp are differentially regulated by carbon source and growth phase. In addition, MppA/Opp is uniquely capable of high-affinity scavenging of muropeptides from growth media, demonstrating that AmpG and MppA/Opp allow for different strategies of recycling PG fragments. Altogether, this work clarifies environmental contexts under which utilizes distinct permeases for PG recycling and explores how scavenging by MppA/Opp could be beneficial in mixed communities.
Topics: Membrane Transport Proteins; Escherichia coli; Peptidoglycan; Bacterial Proteins; Bacteria; Cell Wall
PubMed: 37871219
DOI: 10.1073/pnas.2308940120