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Structural elucidation of the transferase toxin reveals a single-site binding mode for the enzyme.
Sheedlo MJ, Anderson DM, Thomas AK, Lacy DB
(2020) Proc Natl Acad Sci U S A 117: 6139-6144
MeSH Terms: Bacterial Toxins, Clostridium difficile, Cryoelectron Microscopy, Enterotoxins, Protein Conformation, beta-Strand, Protein Multimerization, Transferases
Show Abstract · Added March 24, 2020
is a Gram-positive, pathogenic bacterium and a prominent cause of hospital-acquired diarrhea in the United States. The symptoms of infection are caused by the activity of three large toxins known as toxin A (TcdA), toxin B (TcdB), and the transferase toxin (CDT). Reported here is a 3.8-Å cryo-electron microscopy (cryo-EM) structure of CDT, a bipartite toxin comprised of the proteins CDTa and CDTb. We observe a single molecule of CDTa bound to a CDTb heptamer. The formation of the CDT complex relies on the interaction of an N-terminal adaptor and pseudoenzyme domain of CDTa with six subunits of the CDTb heptamer. CDTb is observed in a preinsertion state, a conformation observed in the transition of prepore to β-barrel pore, although we also observe a single bound CDTa in the prepore and β-barrel conformations of CDTb. The binding interaction appears to prime CDTa for translocation as the adaptor subdomain enters the lumen of the preinsertion state channel. These structural observations advance the understanding of how a single protein, CDTb, can mediate the delivery of a large enzyme, CDTa, into the cytosol of mammalian cells.
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7 MeSH Terms
Structures of the AMPA receptor in complex with its auxiliary subunit cornichon.
Nakagawa T
(2019) Science 366: 1259-1263
MeSH Terms: Animals, Brain, Cryoelectron Microscopy, Glutamic Acid, Ion Channel Gating, Protein Structure, Secondary, Protein Transport, Rats, Receptors, AMPA, Receptors, Glutamate, Synaptic Transmission
Show Abstract · Added March 3, 2020
In the brain, AMPA-type glutamate receptors (AMPARs) form complexes with their auxiliary subunits and mediate the majority of fast excitatory neurotransmission. Signals transduced by these complexes are critical for synaptic plasticity, learning, and memory. The two major categories of AMPAR auxiliary subunits are transmembrane AMPAR regulatory proteins (TARPs) and cornichon homologs (CNIHs); these subunits share little homology and play distinct roles in controlling ion channel gating and trafficking of AMPAR. Here, I report high-resolution cryo-electron microscopy structures of AMPAR in complex with CNIH3. Contrary to its predicted membrane topology, CNIH3 lacks an extracellular domain and instead contains four membrane-spanning helices. The protein-protein interaction interface that dictates channel modulation and the lipids surrounding the complex are revealed. These structures provide insights into the molecular mechanism for ion channel modulation and assembly of AMPAR/CNIH3 complexes.
Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
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11 MeSH Terms
Structural Basis of Protection against H7N9 Influenza Virus by Human Anti-N9 Neuraminidase Antibodies.
Zhu X, Turner HL, Lang S, McBride R, Bangaru S, Gilchuk IM, Yu W, Paulson JC, Crowe JE, Ward AB, Wilson IA
(2019) Cell Host Microbe 26: 729-738.e4
MeSH Terms: Animals, Antibodies, Monoclonal, Antibodies, Neutralizing, Antibodies, Viral, Antiviral Agents, Cryoelectron Microscopy, Epitopes, Humans, Influenza A Virus, H7N9 Subtype, Influenza Vaccines, Neuraminidase, Orthomyxoviridae Infections, Viral Proteins
Show Abstract · Added March 31, 2020
Influenza virus neuraminidase (NA) is a major target for small-molecule antiviral drugs. Antibodies targeting the NA surface antigen could also inhibit virus entry and egress to provide host protection. However, our understanding of the nature and range of target epitopes is limited because of a lack of human antibody structures with influenza neuraminidase. Here, we describe crystal and cryogenic electron microscopy (cryo-EM) structures of NAs from human-infecting avian H7N9 viruses in complex with five human anti-N9 antibodies, systematically defining several antigenic sites and antibody epitope footprints. These antibodies either fully or partially block the NA active site or bind to epitopes distant from the active site while still showing neuraminidase inhibition. The inhibition of antibodies to NAs was further analyzed by glycan array and solution-based NA activity assays. Together, these structural studies provide insights into protection by anti-NA antibodies and templates for the development of NA-based influenza virus vaccines and therapeutics.
Copyright © 2019 Elsevier Inc. All rights reserved.
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13 MeSH Terms
Cryo-EM structures of NKCC1 and hKCC1: a new milestone in the physiology of cation-chloride cotransporters.
Delpire E, Guo J
(2020) Am J Physiol Cell Physiol 318: C225-C237
MeSH Terms: Amino Acid Sequence, Animals, Cations, Chlorides, Cryoelectron Microscopy, Humans, Solute Carrier Family 12, Member 2, Symporters
Show Abstract · Added March 18, 2020
New milestones have been reached in the field of cation-Cl cotransporters with the recently released cryo-electron microscopy (EM) structures of the (zebrafish) Na-K-2Cl cotransporter (NKCC1) and the human K-Cl cotransporter (hKCC1). In this review we provide a brief timeline that identifies the multiple breakthroughs in the field of solute carrier 12 transporters that led to the structure resolution of two of its key members. While cation-Cl cotransporters share the overall architecture of carriers belonging to the amino acid-polyamine-organocation (APC) superfamily and some of their substrate binding sites, several new insights are gained from the two individual structures. A first major feature relates to the largest extracellular domain between transmembrane domain (TMD) 5 and TMD6 of KCC1, which stabilizes the dimer and forms a cap that likely participates in extracellular gating. A second feature is the conservation of the K and Cl binding sites in both structures and evidence of an unexpected second Cl coordination site in the KCC1 structure. Structural data are discussed in the context of previously published studies that examined the basic and kinetics properties of these cotransport mechanisms. A third characteristic is the evidence of an extracellular gate formed by conserved salt bridges between charged residues located toward the end of TMD3 and TMD4 in both transporters and the existence of an additional neighboring bridge in the hKCC1 structure. A fourth feature of these newly solved structures relates to the multiple points of contacts between the monomer forming the cotransporter homodimer units. These involve the TMDs, the COOH-terminal domains, and the large extracellular loop for hKCC1.
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8 MeSH Terms
Real-time visualization of titin dynamics reveals extensive reversible photobleaching in human induced pluripotent stem cell-derived cardiomyocytes.
Cadar AG, Feaster TK, Bersell KR, Wang L, Hong T, Balsamo JA, Zhang Z, Chun YW, Nam YJ, Gotthardt M, Knollmann BC, Roden DM, Lim CC, Hong CC
(2020) Am J Physiol Cell Physiol 318: C163-C173
MeSH Terms: Adult, Cell Differentiation, Cell Line, Connectin, Fluorescence Recovery After Photobleaching, Humans, Induced Pluripotent Stem Cells, Kinetics, Luminescent Proteins, Male, Microscopy, Fluorescence, Microscopy, Video, Myocytes, Cardiac, Recombinant Fusion Proteins, Reproducibility of Results, Sarcomeres
Show Abstract · Added March 24, 2020
Fluorescence recovery after photobleaching (FRAP) has been useful in delineating cardiac myofilament biology, and innovations in fluorophore chemistry have expanded the array of microscopic assays used. However, one assumption in FRAP is the irreversible photobleaching of fluorescent proteins after laser excitation. Here we demonstrate reversible photobleaching regarding the photoconvertible fluorescent protein mEos3.2. We used CRISPR/Cas9 genome editing in human induced pluripotent stem cells (hiPSCs) to knock-in mEos3.2 into the COOH terminus of titin to visualize sarcomeric titin incorporation and turnover. Upon cardiac induction, the titin-mEos3.2 fusion protein is expressed and integrated in the sarcomeres of hiPSC-derived cardiomyocytes (CMs). STORM imaging shows M-band clustered regions of bound titin-mEos3.2 with few soluble titin-mEos3.2 molecules. FRAP revealed a baseline titin-mEos3.2 fluorescence recovery of 68% and half-life of ~1.2 h, suggesting a rapid exchange of sarcomeric titin with soluble titin. However, paraformaldehyde-fixed and permeabilized titin-mEos3.2 hiPSC-CMs surprisingly revealed a 55% fluorescence recovery. Whole cell FRAP analysis in paraformaldehyde-fixed, cycloheximide-treated, and untreated titin-mEos3.2 hiPSC-CMs displayed no significant differences in fluorescence recovery. FRAP in fixed HEK 293T expressing cytosolic mEos3.2 demonstrates a 58% fluorescence recovery. These data suggest that titin-mEos3.2 is subject to reversible photobleaching following FRAP. Using a mouse titin-eGFP model, we demonstrate that no reversible photobleaching occurs. Our results reveal that reversible photobleaching accounts for the majority of titin recovery in the titin-mEos3.2 hiPSC-CM model and should warrant as a caution in the extrapolation of reliable FRAP data from specific fluorescent proteins in long-term cell imaging.
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16 MeSH Terms
Structural insights into the transition of Clostridioides difficile binary toxin from prepore to pore.
Anderson DM, Sheedlo MJ, Jensen JL, Lacy DB
(2020) Nat Microbiol 5: 102-107
MeSH Terms: ADP Ribose Transferases, Bacterial Proteins, Bacterial Toxins, Caco-2 Cells, Cryoelectron Microscopy, Humans, Models, Molecular, Polysaccharides, Pore Forming Cytotoxic Proteins, Protein Binding, Protein Domains, Protein Multimerization, Receptors, LDL
Show Abstract · Added March 24, 2020
Clostridioides (formerly Clostridium) difficile is a Gram-positive, spore-forming anaerobe and a leading cause of hospital-acquired infection and gastroenteritis-associated death in US hospitals. The disease state is usually preceded by disruption of the host microbiome in response to antibiotic treatment and is characterized by mild to severe diarrhoea. C. difficile infection is dependent on the secretion of one or more AB-type toxins: toxin A (TcdA), toxin B (TcdB) and the C. difficile transferase toxin (CDT). Whereas TcdA and TcdB are considered the primary virulence factors, recent studies suggest that CDT increases the severity of C. difficile infection in some of the most problematic clinical strains. To better understand how CDT functions, we used cryo-electron microscopy to define the structure of CDTb, the cell-binding component of CDT. We obtained structures of several oligomeric forms that highlight the conformational changes that enable conversion from a prepore to a β-barrel pore. The structural analysis also reveals a glycan-binding domain and residues involved in binding the host-cell receptor, lipolysis-stimulated lipoprotein receptor. Together, these results provide a framework to understand how CDT functions at the host cell interface.
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13 MeSH Terms
Cryo-EM structures of the human cation-chloride cotransporter KCC1.
Liu S, Chang S, Han B, Xu L, Zhang M, Zhao C, Yang W, Wang F, Li J, Delpire E, Ye S, Bai XC, Guo J
(2019) Science 366: 505-508
MeSH Terms: Amino Acid Sequence, Animals, Binding Sites, Cryoelectron Microscopy, HEK293 Cells, Humans, Ion Transport, Mice, Molecular Dynamics Simulation, Oocytes, Protein Domains, Protein Multimerization, Protein Structure, Quaternary, Sequence Alignment, Sodium-Potassium-Chloride Symporters, Symporters, Xenopus laevis
Show Abstract · Added March 18, 2020
Cation-chloride cotransporters (CCCs) mediate the coupled, electroneutral symport of cations with chloride across the plasma membrane and are vital for cell volume regulation, salt reabsorption in the kidney, and γ-aminobutyric acid (GABA)-mediated modulation in neurons. Here we present cryo-electron microscopy (cryo-EM) structures of human potassium-chloride cotransporter KCC1 in potassium chloride or sodium chloride at 2.9- to 3.5-angstrom resolution. KCC1 exists as a dimer, with both extracellular and transmembrane domains involved in dimerization. The structural and functional analyses, along with computational studies, reveal one potassium site and two chloride sites in KCC1, which are all required for the ion transport activity. KCC1 adopts an inward-facing conformation, with the extracellular gate occluded. The KCC1 structures allow us to model a potential ion transport mechanism in KCCs and provide a blueprint for drug design.
Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
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17 MeSH Terms
neurons have functional dendritic spines.
Cuentas-Condori A, Mulcahy B, He S, Palumbos S, Zhen M, Miller DM
(2019) Elife 8:
MeSH Terms: Animals, Caenorhabditis elegans, Dendritic Spines, Intravital Microscopy, Microscopy, Electron, Microscopy, Fluorescence, Motor Neurons, Organelles
Show Abstract · Added March 3, 2020
Dendritic spines are specialized postsynaptic structures that transduce presynaptic signals, are regulated by neural activity and correlated with learning and memory. Most studies of spine function have focused on the mammalian nervous system. However, spine-like protrusions have been reported in (Philbrook et al., 2018), suggesting that the experimental advantages of smaller model organisms could be exploited to study the biology of dendritic spines. Here, we used super-resolution microscopy, electron microscopy, live-cell imaging and genetics to show that motor neurons have functional dendritic spines that: (1) are structurally defined by a dynamic actin cytoskeleton; (2) appose presynaptic dense projections; (3) localize ER and ribosomes; (4) display calcium transients triggered by presynaptic activity and propagated by internal Ca stores; (5) respond to activity-dependent signals that regulate spine density. These studies provide a solid foundation for a new experimental paradigm that exploits the power of genetics and live-cell imaging for fundamental studies of dendritic spine morphogenesis and function.
© 2019, Cuentas-Condori et al.
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8 MeSH Terms
Perfusion controls muscle glucose uptake by altering the rate of glucose dispersion in vivo.
McClatchey PM, Williams IM, Xu Z, Mignemi NA, Hughey CC, McGuinness OP, Beckman JA, Wasserman DH
(2019) Am J Physiol Endocrinol Metab 317: E1022-E1036
MeSH Terms: 4-Chloro-7-nitrobenzofurazan, Animals, Blood Flow Velocity, Carbon Radioisotopes, Deoxyglucose, Dextrans, Glucose, Hypoglycemic Agents, Insulin, Intravital Microscopy, Mice, Microcirculation, Microspheres, Muscle, Skeletal, Ultrasonography
Show Abstract · Added March 30, 2020
These studies test, using intravital microscopy (IVM), the hypotheses that perfusion effects on insulin-stimulated muscle glucose uptake (MGU) are ) capillary recruitment independent and ) mediated through the dispersion of glucose rather than insulin. For , capillary perfusion was visualized before and after intravenous insulin. No capillary recruitment was observed. For , mice were treated with vasoactive compounds (sodium nitroprusside, hyaluronidase, and lipopolysaccharide), and dispersion of fluorophores approximating insulin size (10-kDa dextran) and glucose (2-NBDG) was measured using IVM. Subsequently, insulin and 2[C]deoxyglucose were injected and muscle phospho-2[C]deoxyglucose (2[C]DG) accumulation was used as an index of MGU. Flow velocity and 2-NBDG dispersion, but not perfused surface area or 10-kDa dextran dispersion, predicted phospho-2[C]DG accumulation. For , microspheres of the same size and number as are used for contrast-enhanced ultrasound (CEU) studies of capillary recruitment were visualized using IVM. Due to their low concentration, microspheres were present in only a small fraction of blood-perfused capillaries. Microsphere-perfused blood volume correlated to flow velocity. These findings suggest that ) flow velocity rather than capillary recruitment controls microvascular contributions to MGU, ) glucose dispersion is more predictive of MGU than dispersion of insulin-sized molecules, and ) CEU measures regional flow velocity rather than capillary recruitment.
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15 MeSH Terms
Molecular Architecture of the Helicobacter pylori Cag Type IV Secretion System.
Hu B, Khara P, Song L, Lin AS, Frick-Cheng AE, Harvey ML, Cover TL, Christie PJ
(2019) mBio 10:
MeSH Terms: Antigens, Bacterial, Bacterial Proteins, Cryoelectron Microscopy, Genomic Islands, Helicobacter pylori, Humans, Type IV Secretion Systems
Show Abstract · Added July 14, 2019
colonizes about half of humans worldwide, and its presence in the gastric mucosa is associated with an increased risk of gastric adenocarcinoma, gastric lymphoma, and peptic ulcer disease. strains carrying the pathogenicity island (PAI) are associated with increased risk of disease progression. The PAI encodes the Cag type IV secretion system (Cag), which delivers the CagA oncoprotein and other effector molecules into human gastric epithelial cells. We visualized structures of native and mutant Cag machines on the cell envelope by cryoelectron tomography. Individual cells contain multiple Cag nanomachines, each composed of a wheel-shaped outer membrane complex (OMC) with 14-fold symmetry and an inner membrane complex (IMC) with 6-fold symmetry. CagX, CagY, and CagM are required for assembly of the OMC, whereas strains lacking Cag3 and CagT produce outer membrane complexes lacking peripheral components. The IMC, which has never been visualized in detail, is configured as six tiers in cross-section view and three concentric rings surrounding a central channel in end-on view. The IMC contains three T4SS ATPases: (i) VirB4-like CagE, arranged as a hexamer of dimers at the channel entrance; (ii) a hexamer of VirB11-like Cagα, docked at the base of the CagE hexamer; and (iii) VirD4-like Cagβ and other unspecified Cag subunits, associated with the stacked CagE/Cagα complex and forming the outermost rings. The Cag and recently solved Dot/Icm system comprise new structural prototypes for the T4SS superfamily. Bacterial type IV secretion systems (T4SSs) have been phylogenetically grouped into two subfamilies. The T4ASSs, represented by the VirB/VirD4, include "minimized" machines assembled from 12 VirB- and VirD4-like subunits and compositionally larger systems such as the Cag T4BSSs encompass systems closely related in subunit composition to the Dot/Icm Here, we present structures of native and mutant Cag machines determined by cryoelectron tomography. We identify distinct outer and inner membrane complexes and, for the first time, visualize structural contributions of all three "signature" ATPases of T4SSs at the cytoplasmic entrance of the translocation channel. Despite their evolutionary divergence, the Cag aligns structurally much more closely to the Dot/Icm than an available VirB/VirD4 subcomplex. Our findings highlight the diversity of T4SSs and suggest a structural classification scheme in which T4SSs are grouped as minimized VirB/VirD4-like or larger Cag-like and Dot/Icm-like systems.
Copyright © 2019 Hu et al.
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