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Functional Properties of Helicobacter pylori VacA Toxin m1 and m2 Variants.
Caston RR, Sierra JC, Foegeding NJ, Truelock MD, Campbell AM, Frick-Cheng AE, Bimczok D, Wilson KT, McClain MS, Cover TL
(2020) Infect Immun 88:
MeSH Terms: Amino Acid Sequence, Bacterial Proteins, Bacterial Toxins, Gene Expression Regulation, Bacterial, Genetic Variation, Helicobacter Infections, Helicobacter pylori, Humans, Protein Domains, Protein Multimerization, Protein Transport, Vacuoles
Show Abstract · Added April 15, 2020
colonizes the gastric mucosa and secretes a pore-forming toxin (VacA). Two main types of VacA, m1 and m2, can be distinguished by phylogenetic analysis. Type m1 forms of VacA have been extensively studied, but there has been relatively little study of m2 forms. In this study, we generated strains producing chimeric proteins in which VacA m1 segments of a parental strain were replaced by corresponding m2 sequences. In comparison to the parental m1 VacA protein, a chimeric protein (designated m2/m1) containing m2 sequences in the N-terminal portion of the m region was less potent in causing vacuolation of HeLa cells, AGS gastric cells, and AZ-521 duodenal cells and had reduced capacity to cause membrane depolarization or death of AZ-521 cells. Consistent with the observed differences in activity, the chimeric m2/m1 VacA protein bound to cells at reduced levels compared to the binding levels of the parental m1 protein. The presence of two strain-specific insertions or deletions within or adjacent to the m region did not influence toxin activity. Experiments with human gastric organoids grown as monolayers indicated that m1 and m2/m1 forms of VacA had similar cell-vacuolating activities. Interestingly, both forms of VacA bound preferentially to the basolateral surface of organoid monolayers and caused increased cell vacuolation when interacting with the basolateral surface compared to the apical surface. These data provide insights into functional correlates of sequence variation in the VacA midregion (m region).
Copyright © 2020 American Society for Microbiology.
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12 MeSH Terms
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, Clostridioides 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
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
Cryo-EM Analysis Reveals Structural Basis of Helicobacter pylori VacA Toxin Oligomerization.
Su M, Erwin AL, Campbell AM, Pyburn TM, Salay LE, Hanks JL, Lacy DB, Akey DL, Cover TL, Ohi MD
(2019) J Mol Biol 431: 1956-1965
MeSH Terms: Bacterial Proteins, Cryoelectron Microscopy, Helicobacter Infections, Helicobacter pylori, Humans, Models, Molecular, Protein Conformation, Protein Multimerization
Show Abstract · Added April 11, 2019
Helicobacter pylori colonizes the human stomach and contributes to the development of gastric cancer and peptic ulcer disease. H. pylori secretes a pore-forming toxin called vacuolating cytotoxin A (VacA), which contains two domains (p33 and p55) and assembles into oligomeric structures. Using single-particle cryo-electron microscopy, we have determined low-resolution structures of a VacA dodecamer and heptamer, as well as a 3.8-Å structure of the VacA hexamer. These analyses show that VacA p88 consists predominantly of a right-handed beta-helix that extends from the p55 domain into the p33 domain. We map the regions of p33 and p55 involved in hexamer assembly, model how interactions between protomers support heptamer formation, and identify surfaces of VacA that likely contact membrane. This work provides structural insights into the process of VacA oligomerization and identifies regions of VacA protomers that are predicted to contact the host cell surface during channel formation.
Copyright © 2019 Elsevier Ltd. All rights reserved.
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8 MeSH Terms
An alternative N-terminal fold of the intestine-specific annexin A13a induces dimerization and regulates membrane-binding.
McCulloch KM, Yamakawa I, Shifrin DA, McConnell RE, Foegeding NJ, Singh PK, Mao S, Tyska MJ, Iverson TM
(2019) J Biol Chem 294: 3454-3463
MeSH Terms: Animals, Annexins, Cell Membrane, Epithelial Cells, Humans, Hydrogen-Ion Concentration, Intestinal Mucosa, Intestines, Liposomes, Mice, Models, Molecular, Organ Specificity, Protein Binding, Protein Conformation, alpha-Helical, Protein Multimerization, Protein Structure, Quaternary, Protein Transport
Show Abstract · Added April 1, 2019
Annexin proteins function as Ca-dependent regulators of membrane trafficking and repair that may also modulate membrane curvature. Here, using high-resolution confocal imaging, we report that the intestine-specific annexin A13 (ANX A13) localizes to the tips of intestinal microvilli and determined the crystal structure of the ANX A13a isoform to 2.6 Å resolution. The structure revealed that the N terminus exhibits an alternative fold that converts the first two helices and the associated helix-loop-helix motif into a continuous α-helix, as stabilized by a domain-swapped dimer. We also found that the dimer is present in solution and partially occludes the membrane-binding surfaces of annexin, suggesting that dimerization may function as a means for regulating membrane binding. Accordingly, as revealed by binding and cellular localization assays, ANX A13a variants that favor a monomeric state exhibited increased membrane association relative to variants that favor the dimeric form. Together, our findings support a mechanism for how the association of the ANX A13a isoform with the membrane is regulated.
© 2019 McCulloch et al.
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17 MeSH Terms
Bid maintains mitochondrial cristae structure and function and protects against cardiac disease in an integrative genomics study.
Salisbury-Ruf CT, Bertram CC, Vergeade A, Lark DS, Shi Q, Heberling ML, Fortune NL, Okoye GD, Jerome WG, Wells QS, Fessel J, Moslehi J, Chen H, Roberts LJ, Boutaud O, Gamazon ER, Zinkel SS
(2018) Elife 7:
MeSH Terms: Animals, Apoptosis, BH3 Interacting Domain Death Agonist Protein, Beclin-1, Cell Respiration, Fibrosis, Gene Expression Regulation, Genome-Wide Association Study, Genomics, Heart Diseases, Heart Ventricles, Humans, Mice, Inbred C57BL, Mitochondria, Mitochondrial Proton-Translocating ATPases, Mutation, Myeloid Progenitor Cells, Myocardial Infarction, Myocytes, Cardiac, Polymorphism, Single Nucleotide, Protein Multimerization, Protein Structure, Secondary, Protein Subunits, Reactive Oxygen Species, Reproducibility of Results, Up-Regulation
Show Abstract · Added December 11, 2018
Bcl-2 family proteins reorganize mitochondrial membranes during apoptosis, to form pores and rearrange cristae. In vitro and in vivo analysis integrated with human genetics reveals a novel homeostatic mitochondrial function for Bcl-2 family protein Bid. Loss of full-length Bid results in apoptosis-independent, irregular cristae with decreased respiration. mice display stress-induced myocardial dysfunction and damage. A gene-based approach applied to a biobank, validated in two independent GWAS studies, reveals that decreased genetically determined BID expression associates with myocardial infarction (MI) susceptibility. Patients in the bottom 5% of the expression distribution exhibit >4 fold increased MI risk. Carrier status with nonsynonymous variation in Bid's membrane binding domain, Bid, associates with MI predisposition. Furthermore, Bid but not Bid associates with Mcl-1, previously implicated in cristae stability; decreased MCL-1 expression associates with MI. Our results identify a role for Bid in homeostatic mitochondrial cristae reorganization, that we link to human cardiac disease.
© 2018, Salisbury-Ruf et al.
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26 MeSH Terms
Disrupted structure and aberrant function of CHIP mediates the loss of motor and cognitive function in preclinical models of SCAR16.
Shi CH, Rubel C, Soss SE, Sanchez-Hodge R, Zhang S, Madrigal SC, Ravi S, McDonough H, Page RC, Chazin WJ, Patterson C, Mao CY, Willis MS, Luo HY, Li YS, Stevens DA, Tang MB, Du P, Wang YH, Hu ZW, Xu YM, Schisler JC
(2018) PLoS Genet 14: e1007664
MeSH Terms: Animals, Behavior, Animal, CRISPR-Cas Systems, Cognition, Disease Models, Animal, Female, Humans, Male, Mice, Mice, Inbred C57BL, Models, Molecular, Motor Activity, Mutagenesis, Site-Directed, Phenotype, Point Mutation, Protein Domains, Protein Multimerization, Rats, Rats, Sprague-Dawley, Spinocerebellar Ataxias, Ubiquitin-Protein Ligases
Show Abstract · Added March 26, 2019
CHIP (carboxyl terminus of heat shock 70-interacting protein) has long been recognized as an active member of the cellular protein quality control system given the ability of CHIP to function as both a co-chaperone and ubiquitin ligase. We discovered a genetic disease, now known as spinocerebellar autosomal recessive 16 (SCAR16), resulting from a coding mutation that caused a loss of CHIP ubiquitin ligase function. The initial mutation describing SCAR16 was a missense mutation in the ubiquitin ligase domain of CHIP (p.T246M). Using multiple biophysical and cellular approaches, we demonstrated that T246M mutation results in structural disorganization and misfolding of the CHIP U-box domain, promoting oligomerization, and increased proteasome-dependent turnover. CHIP-T246M has no ligase activity, but maintains interactions with chaperones and chaperone-related functions. To establish preclinical models of SCAR16, we engineered T246M at the endogenous locus in both mice and rats. Animals homozygous for T246M had both cognitive and motor cerebellar dysfunction distinct from those observed in the CHIP null animal model, as well as deficits in learning and memory, reflective of the cognitive deficits reported in SCAR16 patients. We conclude that the T246M mutation is not equivalent to the total loss of CHIP, supporting the concept that disease-causing CHIP mutations have different biophysical and functional repercussions on CHIP function that may directly correlate to the spectrum of clinical phenotypes observed in SCAR16 patients. Our findings both further expand our basic understanding of CHIP biology and provide meaningful mechanistic insight underlying the molecular drivers of SCAR16 disease pathology, which may be used to inform the development of novel therapeutics for this devastating disease.
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GHSR-D2R heteromerization modulates dopamine signaling through an effect on G protein conformation.
Damian M, Pons V, Renault P, M'Kadmi C, Delort B, Hartmann L, Kaya AI, Louet M, Gagne D, Ben Haj Salah K, Denoyelle S, Ferry G, Boutin JA, Wagner R, Fehrentz JA, Martinez J, Marie J, Floquet N, Galès C, Mary S, Hamm HE, Banères JL
(2018) Proc Natl Acad Sci U S A 115: 4501-4506
MeSH Terms: Dopamine, GTP-Binding Protein alpha Subunits, Gi-Go, Humans, Protein Multimerization, Receptors, Dopamine D2, Receptors, Ghrelin, Signal Transduction
Show Abstract · Added March 24, 2020
The growth hormone secretagogue receptor (GHSR) and dopamine receptor (D2R) have been shown to oligomerize in hypothalamic neurons with a significant effect on dopamine signaling, but the molecular processes underlying this effect are still obscure. We used here the purified GHSR and D2R to establish that these two receptors assemble in a lipid environment as a tetrameric complex composed of two each of the receptors. This complex further recruits G proteins to give rise to an assembly with only two G protein trimers bound to a receptor tetramer. We further demonstrate that receptor heteromerization directly impacts on dopamine-mediated Gi protein activation by modulating the conformation of its α-subunit. Indeed, association to the purified GHSR:D2R heteromer triggers a different active conformation of Gαi that is linked to a higher rate of GTP binding and a faster dissociation from the heteromeric receptor. This is an additional mechanism to expand the repertoire of GPCR signaling modulation that could have implications for the control of dopamine signaling in normal and physiopathological conditions.
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Mechanisms of receptor tyrosine kinase activation in cancer.
Du Z, Lovly CM
(2018) Mol Cancer 17: 58
MeSH Terms: Animals, Cell Transformation, Neoplastic, Enzyme Activation, Gene Expression Regulation, Neoplastic, Humans, Ligands, Molecular Targeted Therapy, Mutation, Neoplasms, Phosphorylation, Protein Binding, Protein Interaction Domains and Motifs, Protein Kinase Inhibitors, Protein Multimerization, Receptor Protein-Tyrosine Kinases, Signal Transduction
Show Abstract · Added September 10, 2020
Receptor tyrosine kinases (RTKs) play an important role in a variety of cellular processes including growth, motility, differentiation, and metabolism. As such, dysregulation of RTK signaling leads to an assortment of human diseases, most notably, cancers. Recent large-scale genomic studies have revealed the presence of various alterations in the genes encoding RTKs such as EGFR, HER2/ErbB2, and MET, amongst many others. Abnormal RTK activation in human cancers is mediated by four principal mechanisms: gain-of-function mutations, genomic amplification, chromosomal rearrangements, and / or autocrine activation. In this manuscript, we review the processes whereby RTKs are activated under normal physiological conditions and discuss several mechanisms whereby RTKs can be aberrantly activated in human cancers. Understanding of these mechanisms has important implications for selection of anti-cancer therapies.
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