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Nature Structural & Molecular Biology Jul 2019Monoamine transporters (MATs) regulate neurotransmission via the reuptake of dopamine, serotonin and norepinephrine from extra-neuronal regions and thus maintain... (Review)
Review
Monoamine transporters (MATs) regulate neurotransmission via the reuptake of dopamine, serotonin and norepinephrine from extra-neuronal regions and thus maintain neurotransmitter homeostasis. As targets of a wide range of compounds, including antidepressants, substances of abuse and drugs for neuropsychiatric and neurodegenerative disorders, their mechanism of action and their modulation by small molecules have long been of broad interest. Recent advances in the structural characterization of dopamine and serotonin transporters have opened the way for structure-based modeling and simulations, which, together with experimental data, now provide mechanistic understanding of their transport function and interactions. Here we review recent progress in the elucidation of the structural dynamics of MATs and their conformational landscape and transitions, as well as allosteric regulation mechanisms.
Topics: Allosteric Regulation; Animals; Binding Sites; Dopamine Plasma Membrane Transport Proteins; Drug Discovery; Humans; Models, Molecular; Norepinephrine Plasma Membrane Transport Proteins; Protein Conformation; Serotonin Plasma Membrane Transport Proteins
PubMed: 31270469
DOI: 10.1038/s41594-019-0253-7 -
Journal of Molecular Biology Aug 2021The synthesis, folding, and function of membrane transport proteins are critical factors for defining cellular physiology. Since the stability of these proteins evolved... (Review)
Review
The synthesis, folding, and function of membrane transport proteins are critical factors for defining cellular physiology. Since the stability of these proteins evolved amidst the lipid bilayer, it is no surprise that we are finding that many of these membrane proteins demonstrate coupling of their structure or activity in some way to the membrane. More and more transporter structures are being determined with some information about the surrounding membrane, and computational modeling is providing further molecular details about these solvation structures. Thus, the field is moving towards identifying which molecular mechanisms - lipid interactions, membrane perturbations, differential solvation, and bulk membrane effects - are involved in linking membrane energetics to transporter stability and function. In this review, we present an overview of these mechanisms and the growing evidence that the lipid bilayer is a major determinant of the fold, form, and function of membrane transport proteins in membranes.
Topics: Cell Membrane; Lipid Bilayers; Membrane Transport Proteins; Models, Molecular; Protein Folding; Structure-Activity Relationship
PubMed: 34139219
DOI: 10.1016/j.jmb.2021.167103 -
Molecular Microbiology Apr 2021Both isomeric forms of alanine play a crucial role in bacterial growth and viability; the L-isomer of this amino acid is one of the building blocks for protein...
Both isomeric forms of alanine play a crucial role in bacterial growth and viability; the L-isomer of this amino acid is one of the building blocks for protein synthesis, and the D-isomer is incorporated into the bacterial cell wall. Despite a long history of genetic manipulation of Bacillus subtilis using auxotrophic markers, the genes involved in alanine metabolism have not been characterized fully. In this work, we genetically characterized the major enzymes involved in B. subtilis alanine biosynthesis and identified an alanine permease, AlaP (YtnA), which we show has a major role in the assimilation of D-alanine from the environment. Our results provide explanations for the puzzling fact that growth of B. subtilis does not result in the significant accumulation of extracellular D-alanine. Interestingly, we find that in B. subtilis, unlike E. coli where multiple enzymes have a biochemical activity that can generate alanine, the primary synthetic enzyme for alanine is encoded by alaT, although a second gene, dat, can support slow growth of an L-alanine auxotroph. However, our results also show that Dat mediates the synthesis of D-alanine and its activity is influenced by the abundance of L-alanine. This work provides valuable insights into alanine metabolism that suggests that the relative abundance of D- and L-alanine might be linked with cytosolic pool of D and L-glutamate, thereby coupling protein and cell envelope synthesis with the metabolic status of the cell. The results also suggest that, although some of the purified enzymes involved in alanine biosynthesis have been shown to catalyze reversible reactions in vitro, most of them function unidirectionally in vivo.
Topics: Alanine; Amino Acid Transport Systems; Bacillus subtilis; Bacterial Proteins; Biosynthetic Pathways; Membrane Transport Proteins; Transaminases
PubMed: 33155333
DOI: 10.1111/mmi.14640 -
The Journal of Cell Biology Jul 2019The liver performs numerous vital functions, including the detoxification of blood before access to the brain while simultaneously secreting and internalizing scores of... (Review)
Review
The liver performs numerous vital functions, including the detoxification of blood before access to the brain while simultaneously secreting and internalizing scores of proteins and lipids to maintain appropriate blood chemistry. Furthermore, the liver also synthesizes and secretes bile to enable the digestion of food. These diverse attributes are all performed by hepatocytes, the parenchymal cells of the liver. As predicted, these cells possess a remarkably well-developed and complex membrane trafficking machinery that is dedicated to moving specific cargos to their correct cellular locations. Importantly, while most epithelial cells secrete nascent proteins directionally toward a single lumen, the hepatocyte secretes both proteins and bile concomitantly at its basolateral and apical domains, respectively. In this review, we will detail these central features of the hepatocyte and highlight how membrane transport processes play a key role in healthy liver function and how they are affected by disease.
Topics: Animals; Cell Membrane; Cell Movement; Hepatocytes; Humans; Liver; Membrane Transport Proteins; Parenchymal Tissue; Protein Transport
PubMed: 31201265
DOI: 10.1083/jcb.201903090 -
MBio Feb 2023Flucytosine (5-FC) is an antifungal agent commonly used for treatment of cryptococcosis and several other systemic mycoses. In fungi, cytosine permease and cytosine...
Flucytosine (5-FC) is an antifungal agent commonly used for treatment of cryptococcosis and several other systemic mycoses. In fungi, cytosine permease and cytosine deaminase are known major players in flucytosine resistance by regulating uptake and deamination of 5-FC, respectively. Cryptococcus species have three paralogs each of cytosine permease ( and ) and cytosine deaminase ( and ). As in other fungi, we found and to be the primary cytosine deaminase and permease gene, respectively, in C. neoformans H99 (VNI), C. gattii R265 (VGIIa) and WM276 (VGI). However, when various amino acids were used as the sole nitrogen source, C. neoformans and C. gattii diverged in the function of and Though there was some lineage-dependent variability, the two genes functioned as the secondary permease and deaminase, respectively, only in C. gattii when the nitrogen source was arginine, asparagine, or proline. Additionally, the expression of genes, excluding , was under nitrogen catabolic repression in the presence of NH. Functional analysis of and gene deletion constructs demonstrated that these two genes regulate the expression of each permease and deaminase genes individually. Furthermore, the expression levels of and under different amino acids corroborated the 5-FC susceptibility in or background. Thus, the mechanism of 5-FC resistance in C. gattii under diverse nitrogen conditions is orchestrated by two transcription factors of GATA family, cytosine permease and deaminase genes. 5-FC is a commonly used antifungal drug for treatment of cryptococcosis caused by Cryptococcus neoformans and C. gattii species complexes. When various amino acids were used as the sole nitrogen source for growth, we found lineage dependent differences in 5-FC susceptibility. Deletion of the classical cytosine permease () and deaminase () genes caused increased 5-FC resistance in all tested nitrogen sources in C. neoformans but not in C. gattii. Furthermore, we demonstrate that the two GATA family transcription factor genes and are involved in the nitrogen-source dependent 5-FC resistance by regulating the expression of the paralogs of cytosine permease and deaminase genes. Our study not only identifies the new function of paralogs of the cytosine permease and deaminase and the role of their regulatory transcription factors but also denotes the differences in the mechanism of 5-FC resistance among the two etiologic agents of cryptococcosis under different nitrogen sources.
Topics: Flucytosine; Nitrogen; Cytosine Deaminase; Antifungal Agents; Cryptococcus neoformans; Cryptococcus gattii; Cryptococcosis; Amino Acids; Membrane Transport Proteins; Transcription Factors; Microbial Sensitivity Tests
PubMed: 36656038
DOI: 10.1128/mbio.03451-22 -
The Journal of General Physiology Jul 2019The lactose permease (LacY) of is the prototype of the major facilitator superfamily, one of the largest families of membrane transport proteins. Structurally, two... (Review)
Review
The lactose permease (LacY) of is the prototype of the major facilitator superfamily, one of the largest families of membrane transport proteins. Structurally, two pseudo-symmetrical six-helix bundles surround a large internal aqueous cavity. Single binding sites for galactoside and H are positioned at the approximate center of LacY halfway through the membrane at the apex of the internal cavity. These features enable LacY to function by an alternating-access mechanism that can catalyze galactoside/H symport in either direction across the cytoplasmic membrane. The H-binding site is fully protonated under physiological conditions, and subsequent sugar binding causes transition of the ternary complex to an occluded intermediate that can open to either side of the membrane. We review the structural and functional evidence that has provided new insight into the mechanism by which LacY achieves active transport against a concentration gradient.
Topics: Binding Sites; Catabolite Repression; Escherichia coli; Escherichia coli Proteins; Lactose; Monosaccharide Transport Proteins; Protons; Symporters
PubMed: 31147449
DOI: 10.1085/jgp.201912377 -
Molecular Cell Sep 2021Nutrient supply and demand delineate cell behavior in health and disease. Mammalian cells have developed multiple strategies to secure the necessary nutrients that fuel... (Review)
Review
Nutrient supply and demand delineate cell behavior in health and disease. Mammalian cells have developed multiple strategies to secure the necessary nutrients that fuel their metabolic needs. This is more evident upon disruption of homeostasis in conditions such as cancer, when cells display high proliferation rates in energetically challenging conditions where nutritional sources may be scarce. Here, we summarize the main routes of nutrient acquisition that fuel mammalian cells and their implications in tumorigenesis. We argue that the molecular mechanisms of nutrient acquisition not only tip the balance between nutrient supply and demand but also determine cell behavior upon nutrient limitation and energetic stress and contribute to nutrient partitioning and metabolic coordination between different cell types in inflamed or tumorigenic environments.
Topics: ATP-Binding Cassette Transporters; Animals; Biological Transport; Carcinogenesis; Cell Membrane; Homeostasis; Humans; Membrane Transport Proteins; Neoplasms; Nutrients; Solute Carrier Proteins
PubMed: 34547236
DOI: 10.1016/j.molcel.2021.08.026 -
International Journal of Molecular... Jun 2020Over the last years, nontuberculous mycobacteria (NTM) have emerged as important human pathogens. Infections caused by NTM are often difficult to treat due to an... (Review)
Review
Over the last years, nontuberculous mycobacteria (NTM) have emerged as important human pathogens. Infections caused by NTM are often difficult to treat due to an intrinsic multidrug resistance for the presence of a lipid-rich outer membrane, thus encouraging an urgent need for the development of new drugs for the treatment of mycobacterial infections. Efflux pumps (EPs) are important elements that are involved in drug resistance by preventing intracellular accumulation of antibiotics. A promising strategy to decrease drug resistance is the inhibition of EP activity by EP inhibitors (EPIs), compounds that are able to increase the intracellular concentration of antimicrobials. Recently, attention has been focused on identifying EPIs in mycobacteria that could be used in combination with drugs. The aim of the present review is to provide an overview of the current knowledge on EPs and EPIs in NTM and also, the effect of potential EPIs as well as their combined use with antimycobacterial drugs in various NTM species are described.
Topics: Anti-Bacterial Agents; Drug Resistance, Bacterial; Drug Synergism; Humans; Membrane Transport Proteins; Microbial Sensitivity Tests; Mycobacterium Infections, Nontuberculous; Nontuberculous Mycobacteria; Small Molecule Libraries
PubMed: 32545436
DOI: 10.3390/ijms21124191 -
Chemical Reviews May 2021The biology of mycobacteria is dominated by a complex cell envelope of unique composition and structure and of exceptionally low permeability. This cell envelope is the... (Review)
Review
The biology of mycobacteria is dominated by a complex cell envelope of unique composition and structure and of exceptionally low permeability. This cell envelope is the basis of many of the pathogenic features of mycobacteria and the site of susceptibility and resistance to many antibiotics and host defense mechanisms. This review is focused on the transporters that assemble and functionalize this complex structure. It highlights both the progress and the limits of our understanding of how (lipo)polysaccharides, (glyco)lipids, and other bacterial secretion products are translocated across the different layers of the cell envelope to their final extra-cytoplasmic location. It further describes some of the unique strategies evolved by mycobacteria to import nutrients and other products through this highly impermeable barrier.
Topics: Cell Membrane; Cell Wall; Membrane Lipids; Membrane Transport Proteins; Mycobacterium; Organelle Biogenesis
PubMed: 33170669
DOI: 10.1021/acs.chemrev.0c00869 -
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