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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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Structural basis of a potent human monoclonal antibody against Zika virus targeting a quaternary epitope.
Long F, Doyle M, Fernandez E, Miller AS, Klose T, Sevvana M, Bryan A, Davidson E, Doranz BJ, Kuhn RJ, Diamond MS, Crowe JE, Rossmann MG
(2019) Proc Natl Acad Sci U S A 116: 1591-1596
MeSH Terms: Animals, Antibodies, Monoclonal, Antibodies, Neutralizing, Antibodies, Viral, Cryoelectron Microscopy, Disease Models, Animal, Epitopes, Humans, Male, Mice, Mice, Inbred C57BL, Vaccination, Viral Envelope Proteins, Zika Virus, Zika Virus Infection
Show Abstract · Added March 31, 2019
Zika virus (ZIKV) is a major human pathogen and member of the genus in the Flaviviridae family. In contrast to most other insect-transmitted flaviviruses, ZIKV also can be transmitted sexually and from mother to fetus in humans. During recent outbreaks, ZIKV infections have been linked to microcephaly, congenital disease, and Guillain-Barré syndrome. Neutralizing antibodies have potential as therapeutic agents. We report here a 4-Å-resolution cryo-electron microscopy structure of the ZIKV virion in complex with Fab fragments of the potently neutralizing human monoclonal antibody ZIKV-195. The footprint of the ZIKV-195 Fab fragment expands across two adjacent envelope (E) protein protomers. ZIKV neutralization by this antibody is presumably accomplished by cross-linking the E proteins, which likely prevents formation of E protein trimers required for fusion of the viral and cellular membranes. A single dose of ZIKV-195 administered 5 days after virus inoculation showed marked protection against lethality in a stringent mouse model of infection.
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Cryo-EM structure of the cytoplasmic domain of murine transient receptor potential cation channel subfamily C member 6 (TRPC6).
Azumaya CM, Sierra-Valdez F, Cordero-Morales JF, Nakagawa T
(2018) J Biol Chem 293: 10381-10391
MeSH Terms: Animals, Cryoelectron Microscopy, Cytoplasm, HEK293 Cells, Humans, Mice, Mutation, Protein Domains, TRPC6 Cation Channel
Show Abstract · Added April 10, 2019
The kidney maintains the internal milieu by regulating the retention and excretion of proteins, ions, and small molecules. The glomerular podocyte forms the slit diaphragm of the ultrafiltration filter, whose damage leads to progressive kidney failure and focal segmental glomerulosclerosis (FSGS). The canonical transient receptor potential 6 (TRPC6) ion channel is expressed in the podocyte, and mutations in its cytoplasmic domain cause FSGS in humans. evaluation of disease-causing mutations in TRPC6 has revealed that these genetic alterations result in abnormal ion channel gating. However, the mechanism whereby the cytoplasmic domain modulates TRPC6 function is largely unknown. Here, we report a cryo-EM structure of the cytoplasmic domain of murine TRPC6 at 3.8 Å resolution. The cytoplasmic fold of TRPC6 is characterized by an inverted dome-like chamber pierced by four radial horizontal helices that converge into a vertical coiled-coil at the central axis. Unlike other TRP channels, TRPC6 displays a unique domain swap that occurs at the junction of the horizontal helices and coiled-coil. Multiple FSGS mutations converge at the buried interface between the vertical coiled-coil and the ankyrin repeats, which form the dome, suggesting these regions are critical for allosteric gating modulation. This functionally critical interface is a potential target for drug design. Importantly, dysfunction in other family members leads to learning deficits (TRPC1/4/5) and ataxia (TRPC3). Our data provide a structural framework for the mechanistic investigation of the TRPC family.
© 2018 Azumaya et al.
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A human antibody against Zika virus crosslinks the E protein to prevent infection.
Hasan SS, Miller A, Sapparapu G, Fernandez E, Klose T, Long F, Fokine A, Porta JC, Jiang W, Diamond MS, Crowe JE, Kuhn RJ, Rossmann MG
(2017) Nat Commun 8: 14722
MeSH Terms: Antibodies, Monoclonal, Antibodies, Neutralizing, Antibodies, Viral, Binding Sites, Cryoelectron Microscopy, HEK293 Cells, Humans, Models, Molecular, Protein Binding, Protein Domains, Protein Multimerization, Viral Structural Proteins, Zika Virus, Zika Virus Infection
Show Abstract · Added April 13, 2017
The recent Zika virus (ZIKV) epidemic has been linked to unusual and severe clinical manifestations including microcephaly in fetuses of infected pregnant women and Guillian-Barré syndrome in adults. Neutralizing antibodies present a possible therapeutic approach to prevent and control ZIKV infection. Here we present a 6.2 Å resolution three-dimensional cryo-electron microscopy (cryoEM) structure of an infectious ZIKV (strain H/PF/2013, French Polynesia) in complex with the Fab fragment of a highly therapeutic and neutralizing human monoclonal antibody, ZIKV-117. The antibody had been shown to prevent fetal infection and demise in mice. The structure shows that ZIKV-117 Fabs cross-link the monomers within the surface E glycoprotein dimers as well as between neighbouring dimers, thus preventing the reorganization of E protein monomers into fusogenic trimers in the acidic environment of endosomes.
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While the revolution will not be crystallized, biochemistry reigns supreme.
Takizawa Y, Binshtein E, Erwin AL, Pyburn TM, Mittendorf KF, Ohi MD
(2017) Protein Sci 26: 69-81
MeSH Terms: Cryoelectron Microscopy, Crystallography, X-Ray, Models, Molecular
Show Abstract · Added April 26, 2017
Single-particle cryo-electron microscopy (EM) is currently gaining attention for the ability to calculate structures that reach sub-5 Å resolutions; however, the technique is more than just an alternative approach to X-ray crystallography. Molecular machines work via dynamic conformational changes, making structural flexibility the hallmark of function. While the dynamic regions in molecules are essential, they are also the most challenging to structurally characterize. Single-particle EM has the distinct advantage of being able to directly visualize purified molecules without the formation of ordered arrays of molecules locked into identical conformations. Additionally, structures determined using single-particle EM can span resolution ranges from very low- to atomic-levels (>30-1.8 Å), sometimes even in the same structure. The ability to accommodate various resolutions gives single-particle EM the unique capacity to structurally characterize dynamic regions of biological molecules, thereby contributing essential structural information needed for the development of molecular models that explain function. Further, many important molecular machines are intrinsically dynamic and compositionally heterogeneous. Structures of these complexes may never reach sub-5 Å resolutions due to this flexibility required for function. Thus, the biochemical quality of the sample, as well as, the calculation and interpretation of low- to mid-resolution cryo-EM structures (30-8 Å) remains critical for generating insights into the architecture of many challenging biological samples that cannot be visualized using alternative techniques.
© 2016 The Protein Society.
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Structures of Ebola virus GP and sGP in complex with therapeutic antibodies.
Pallesen J, Murin CD, de Val N, Cottrell CA, Hastie KM, Turner HL, Fusco ML, Flyak AI, Zeitlin L, Crowe JE, Andersen KG, Saphire EO, Ward AB
(2016) Nat Microbiol 1: 16128
MeSH Terms: Amino Acid Sequence, Antibodies, Monoclonal, Antibody Formation, Cross Reactions, Cryoelectron Microscopy, Ebolavirus, Epitopes, Glycoproteins, Hemorrhagic Fever, Ebola, Humans, Membrane Glycoproteins, Models, Structural, Mutation, Protein Multimerization, Sequence Alignment, Viral Proteins
Show Abstract · Added April 13, 2017
The Ebola virus (EBOV) GP gene encodes two glycoproteins. The major product is a soluble, dimeric glycoprotein (sGP) that is secreted abundantly. Despite the abundance of sGP during infection, little is known regarding its structure or functional role. A minor product, resulting from transcriptional editing, is the transmembrane-anchored, trimeric viral surface glycoprotein (GP). GP mediates attachment to and entry into host cells, and is the intended target of antibody therapeutics. Because large portions of sequence are shared between GP and sGP, it has been hypothesized that sGP may potentially subvert the immune response or may contribute to pathogenicity. In this study, we present cryo-electron microscopy structures of GP and sGP in complex with GP-specific and GP/sGP cross-reactive antibodies undergoing human clinical trials. The structure of the sGP dimer presented here, in complex with both an sGP-specific antibody and a GP/sGP cross-reactive antibody, permits us to unambiguously assign the oligomeric arrangement of sGP and compare its structure and epitope presentation to those of GP. We also provide biophysical evaluation of naturally occurring GP/sGP mutations that fall within the footprints identified by our high-resolution structures. Taken together, our data provide a detailed and more complete picture of the accessible Ebolavirus glycoprotein landscape and a structural basis to evaluate patient and vaccine antibody responses towards differently structured products of the GP gene.
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Activation of NMDA receptors and the mechanism of inhibition by ifenprodil.
Tajima N, Karakas E, Grant T, Simorowski N, Diaz-Avalos R, Grigorieff N, Furukawa H
(2016) Nature 534: 63-8
MeSH Terms: Animals, Apoproteins, Cryoelectron Microscopy, Crystallography, X-Ray, Electrophysiology, Ion Channel Gating, Ligands, Models, Molecular, Piperidines, Protein Conformation, Protein Multimerization, Protein Subunits, Rats, Receptors, N-Methyl-D-Aspartate
Show Abstract · Added April 3, 2018
The physiology of N-methyl-d-aspartate (NMDA) receptors is fundamental to brain development and function. NMDA receptors are ionotropic glutamate receptors that function as heterotetramers composed mainly of GluN1 and GluN2 subunits. Activation of NMDA receptors requires binding of neurotransmitter agonists to a ligand-binding domain (LBD) and structural rearrangement of an amino-terminal domain (ATD). Recent crystal structures of GluN1-GluN2B NMDA receptors bound to agonists and an allosteric inhibitor, ifenprodil, represent the allosterically inhibited state. However, how the ATD and LBD move to activate the NMDA receptor ion channel remains unclear. Here we applied X-ray crystallography, single-particle electron cryomicroscopy and electrophysiology to rat NMDA receptors to show that, in the absence of ifenprodil, the bi-lobed structure of GluN2 ATD adopts an open conformation accompanied by rearrangement of the GluN1-GluN2 ATD heterodimeric interface, altering subunit orientation in the ATD and LBD and forming an active receptor conformation that gates the ion channel.
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Broadly Neutralizing Alphavirus Antibodies Bind an Epitope on E2 and Inhibit Entry and Egress.
Fox JM, Long F, Edeling MA, Lin H, van Duijl-Richter MKS, Fong RH, Kahle KM, Smit JM, Jin J, Simmons G, Doranz BJ, Crowe JE, Fremont DH, Rossmann MG, Diamond MS
(2015) Cell 163: 1095-1107
MeSH Terms: Alphavirus, Alphavirus Infections, Amino Acid Sequence, Animals, Antibodies, Monoclonal, Antibodies, Neutralizing, Antibodies, Viral, Chikungunya virus, Cryoelectron Microscopy, Epitopes, Glycoproteins, Humans, Immunoglobulin Fab Fragments, Mice, Models, Molecular, Molecular Sequence Data, Protein Structure, Tertiary, Sequence Alignment, Viral Envelope Proteins, Viral Vaccines, Virus Internalization
Show Abstract · Added January 26, 2016
We screened a panel of mouse and human monoclonal antibodies (MAbs) against chikungunya virus and identified several with inhibitory activity against multiple alphaviruses. Passive transfer of broadly neutralizing MAbs protected mice against infection by chikungunya, Mayaro, and O'nyong'nyong alphaviruses. Using alanine-scanning mutagenesis, loss-of-function recombinant proteins and viruses, and multiple functional assays, we determined that broadly neutralizing MAbs block multiple steps in the viral lifecycle, including entry and egress, and bind to a conserved epitope on the B domain of the E2 glycoprotein. A 16 Å resolution cryo-electron microscopy structure of a Fab fragment bound to CHIKV E2 B domain provided an explanation for its neutralizing activity. Binding to the B domain was associated with repositioning of the A domain of E2 that enabled cross-linking of neighboring spikes. Our results suggest that B domain antigenic determinants could be targeted for vaccine or antibody therapeutic development against multiple alphaviruses of global concern.
Copyright © 2015 Elsevier Inc. All rights reserved.
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Cryo-EM structures elucidate neutralizing mechanisms of anti-chikungunya human monoclonal antibodies with therapeutic activity.
Long F, Fong RH, Austin SK, Chen Z, Klose T, Fokine A, Liu Y, Porta J, Sapparapu G, Akahata W, Doranz BJ, Crowe JE, Diamond MS, Rossmann MG
(2015) Proc Natl Acad Sci U S A 112: 13898-903
MeSH Terms: Antibodies, Monoclonal, Antibodies, Neutralizing, Chikungunya Fever, Chikungunya virus, Cryoelectron Microscopy, Humans, Protein Conformation
Show Abstract · Added January 26, 2016
Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes severe acute and chronic disease in humans. Although highly inhibitory murine and human monoclonal antibodies (mAbs) have been generated, the structural basis of their neutralizing activity remains poorly characterized. Here, we determined the cryo-EM structures of chikungunya virus-like particles complexed with antibody fragments (Fab) of two highly protective human mAbs, 4J21 and 5M16, that block virus fusion with host membranes. Both mAbs bind primarily to sites within the A and B domains, as well as to the B domain's β-ribbon connector of the viral glycoprotein E2. The footprints of these antibodies on the viral surface were consistent with results from loss-of-binding studies using an alanine scanning mutagenesis-based epitope mapping approach. The Fab fragments stabilized the position of the B domain relative to the virus, particularly for the complex with 5M16. This finding is consistent with a mechanism of neutralization in which anti-CHIKV mAbs that bridge the A and B domains impede movement of the B domain away from the underlying fusion loop on the E1 glycoprotein and therefore block the requisite pH-dependent fusion of viral and host membranes.
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7 MeSH Terms
DENGUE VIRUS. Cryo-EM structure of an antibody that neutralizes dengue virus type 2 by locking E protein dimers.
Fibriansah G, Ibarra KD, Ng TS, Smith SA, Tan JL, Lim XN, Ooi JS, Kostyuchenko VA, Wang J, de Silva AM, Harris E, Crowe JE, Lok SM
(2015) Science 349: 88-91
MeSH Terms: Animals, Antibodies, Monoclonal, Antibodies, Neutralizing, Coinfection, Cross Reactions, Cryoelectron Microscopy, Dengue Virus, Disease Models, Animal, Epitopes, Humans, Mice, Serogroup, Viral Envelope Proteins
Show Abstract · Added January 26, 2016
There are four closely-related dengue virus (DENV) serotypes. Infection with one serotype generates antibodies that may cross-react and enhance infection with other serotypes in a secondary infection. We demonstrated that DENV serotype 2 (DENV2)-specific human monoclonal antibody (HMAb) 2D22 is therapeutic in a mouse model of antibody-enhanced severe dengue disease. We determined the cryo-electron microscopy (cryo-EM) structures of HMAb 2D22 complexed with two different DENV2 strains. HMAb 2D22 binds across viral envelope (E) proteins in the dimeric structure, which probably blocks the E protein reorganization required for virus fusion. HMAb 2D22 "locks" two-thirds of or all dimers on the virus surface, depending on the strain, but neutralizes these DENV2 strains with equal potency. The epitope defined by HMAb 2D22 is a potential target for vaccines and therapeutics.
Copyright © 2015, American Association for the Advancement of Science.
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13 MeSH Terms