scholarly journals Variants of Escherichia coli Subtilase Cytotoxin Subunits Show Differences in Complex Formation In Vitro

Toxins ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 703 ◽  
Author(s):  
Maike Krause ◽  
Katharina Sessler ◽  
Anna Kaziales ◽  
Richard Grahl ◽  
Sabrina Noettger ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Hela Cells ◽  
Analytical Ultracentrifugation ◽  
Cd Spectroscopy ◽  
Size Exclusion ◽  
Titration Calorimetry ◽  
Target Cells ◽  
Binding Behavior ◽  
Subtilase Cytotoxin

The subtilase cytotoxin (SubAB) of Shiga toxin-producing Escherichia coli (STEC) is a member of the AB5 toxin family. In the current study, we analyzed the formation of active homo- and hetero-complexes of SubAB variants in vitro to characterize the mode of assembly of the subunits. Recombinant SubA1-His, SubB1-His, SubA2-2-His, and SubB2-2-His subunits, and His-tag-free SubA2-2 were separately expressed, purified, and biochemically characterized by circular dichroism (CD) spectroscopy, size-exclusion chromatography (SEC), and analytical ultracentrifugation (aUC). To confirm their biological activity, cytotoxicity assays were performed with HeLa cells. The formation of AB5 complexes was investigated with aUC and isothermal titration calorimetry (ITC). Binding of SubAB2-2-His to HeLa cells was characterized with flow cytometry (FACS). Cytotoxicity experiments revealed that the analyzed recombinant subtilase subunits were biochemically functional and capable of intoxicating HeLa cells. Inhibition of cytotoxicity by Brefeldin A demonstrated that the cleavage is specific. All His-tagged subunits, as well as the non-tagged SubA2-2 subunit, showed the expected secondary structural compositions and oligomerization. Whereas SubAB1-His complexes could be reconstituted in solution, and revealed a Kd value of 3.9 ± 0.8 μmol/L in the lower micromolar range, only transient interactions were observed for the subunits of SubAB2-2-His in solution, which did not result in any binding constant when analyzed with ITC. Additional studies on the binding characteristics of SubAB2-2-His on HeLa cells revealed that the formation of transient complexes improved binding to the target cells. Conclusively, we hypothesize that SubAB variants exhibit different characteristics in their binding behavior to their target cells.

scholarly journals Biochemical, Biophysical, and Mutational Analyses of Subunit Interactions of the Human Cytomegalovirus Nuclear Egress Complex

2009 ◽  
Vol 83 (7) ◽  
pp. 2996-3006 ◽  
Author(s):  
My D. Sam ◽  
Brady T. Evans ◽  
Donald M. Coen ◽  
James M. Hogle
Keyword(s):  
Human Cytomegalovirus ◽  
Protein Interactions ◽  
Analytical Ultracentrifugation ◽  
Size Exclusion ◽  
Titration Calorimetry ◽  
Protein Protein Interactions ◽  
Truncated Form ◽  
Nuclear Egress ◽  
Exclusion Chromatography

ABSTRACT Nuclear egress, the trafficking of herpesvirus nucleocapsids from the nucleus to the cytoplasm, involves two conserved viral proteins that form a complex at the nuclear envelope, referred to as the nuclear egress complex. In human cytomegalovirus, these two proteins are called UL50 and UL53. To study UL50 and UL53 in molecular detail, these proteins were expressed in bacteria and purified. To obtain highly expressed, pure proteins, it was necessary to truncate both constructs based on sequence conservation and predicted secondary structural elements. Size exclusion chromatography and analytical ultracentrifugation studies indicated that the truncated form of UL50 is a monomer in solution, that the truncated form of UL53 is a homodimer, and that, when mixed, the two proteins form a heterodimer. To identify residues of UL53 crucial for homodimerization and for heterodimerization with UL50, we constructed and expressed mutant forms of UL53 containing alanine substitutions in a predicted helix. Isothermal titration calorimetry was used to measure the binding affinities of the UL53 mutants to UL50. UL53 residues, the replacement of which reduced binding to UL50, form a surface on one face of the predicted helix. Moreover, most of the substitutions that reduce UL53-UL50 interactions also reduced homodimerization. Substitutions that reduced the interaction between UL50 and UL53 in vitro also reduced colocalization of full-length UL50 and UL53 at the nuclear rim in transfected cells. These results demonstrate direct protein-protein interactions between these proteins that are likely to be mediated by a helix, and they have implications for understanding nuclear egress and for drug discovery.

scholarly journals Multiple Elements Controlling Adherence of Enterohemorrhagic Escherichia coli O157:H7 to HeLa Cells

2003 ◽  
Vol 71 (9) ◽  
pp. 4985-4995 ◽  
Author(s):  
Alfredo G. Torres ◽  
James B. Kaper
Keyword(s):  
Escherichia Coli ◽  
Hela Cells ◽  
Culture Conditions ◽  
Enterohemorrhagic Escherichia Coli ◽  
Differentially Expressed ◽  
Wild Type ◽  
Transposon Insertion ◽  
Reduced Adherence ◽  
Insertion Mutants

ABSTRACT Adherence of enterohemorrhagic Escherichia coli (EHEC) to the intestinal epithelium is essential for initiation of infection. Intimin is the only factor demonstrated to play a role in intestinal colonization by EHEC O157:H7. Other attempts to identify additional adhesion factors in vitro have been unsuccessful, suggesting that expression of these factors is under tight regulation. We sought to identify genes involved in the control of adherence of EHEC O157:H7 to cultured epithelial cells. A total of 5,000 independent transposon insertion mutants were screened for their ability to adhere to HeLa cells, and 7 mutants were isolated with a markedly enhanced adherence. The mutants adhered at levels 113 to 170% that of the wild-type strain, and analysis of the protein profiles of these mutants revealed several proteins differentially expressed under in vitro culture conditions. We determined the sequence of the differentially expressed proteins and further investigated the function of OmpA, whose expression was increased in a mutant with an insertionally inactivated tcdA gene. An isogenic ompA mutant showed reduced adherence compared to the parent strain. Disruption of the ompA gene in the tdcA mutant strain abolished the hyperadherent phenotype, and anti-OmpA serum inhibited adhesion of wild-type and tdcA mutant strains to HeLa cells. Enhanced adhesion mediated by OmpA was also observed with Caco-2 cells, and anti-OmpA serum blocked adherence to HeLa cells of other EHEC O157:H7 strains. Our results indicate that multiple elements control adherence and OmpA acts as an adhesin in EHEC O157:H7.

scholarly journals Very Long-Chain C24:1 Ceramide Is Increased in Serum Extracellular Vesicles with Aging and Can Induce Senescence in Bone-Derived Mesenchymal Stem Cells

Cells ◽  
2019 ◽  
Vol 8 (1) ◽  
pp. 37 ◽  
Author(s):  
Andrew Khayrullin ◽  
Priyanka Krishnan ◽  
Luis Martinez-Nater ◽  
Bharati Mendhe ◽  
Sadanand Fulzele ◽  
...  
Keyword(s):  
Stem Cells ◽  
Mesenchymal Stem Cells ◽  
Extracellular Vesicles ◽  
Cardiovascular Health ◽  
Rhesus Macaques ◽  
Cell Communication ◽  
Size Exclusion ◽  
Target Cells ◽  
Serum Samples

Extracellular vesicles (EVs), including exosomes and microvesicles, function in cell-to-cell communication through delivery of proteins, lipids and microRNAs to target cells via endocytosis and membrane fusion. These vesicles are enriched in ceramide, a sphingolipid associated with the promotion of cell senescence and apoptosis. We investigated the ceramide profile of serum exosomes from young (24–40 yrs.) and older (75–90 yrs.) women and young (6–10 yrs.) and older (25–30 yrs.) rhesus macaques to define the role of circulating ceramides in the aging process. EVs were isolated using size-exclusion chromatography. Proteomic analysis was used to validate known exosome markers from Exocarta and nanoparticle tracking analysis used to characterize particle size and concentration. Specific ceramide species were identified with lipidomic analysis. Results show a significant increase in the average amount of C24:1 ceramide in EVs from older women (15.4 pmol/sample) compared to those from younger women (3.8 pmol/sample). Results were similar in non-human primate serum samples with increased amounts of C24:1 ceramide (9.3 pmol/sample) in older monkeys compared to the younger monkeys (1.8 pmol/sample). In vitro studies showed that primary bone-derived mesenchymal stem cells (BMSCs) readily endocytose serum EVs, and serum EVs loaded with C24:1 ceramide can induce BMSC senescence. Elevated ceramide levels have been associated with poor cardiovascular health and memory impairment in older adults. Our data suggest that circulating EVs carrying C24:1 ceramide may contribute directly to cell non-autonomous aging.

scholarly journals Enzymatic Synthesis and Functional Characterization of Bioactive Microcin C-Like Compounds with Altered Peptide Sequence and Length

2015 ◽  
Vol 197 (19) ◽  
pp. 3133-3141 ◽  
Author(s):  
Olga Bantysh ◽  
Marina Serebryakova ◽  
Inna Zukher ◽  
Alexey Kulikovsky ◽  
Darya Tsibulskaya ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Biological Activity ◽  
Functional Characterization ◽  
Trna Synthetase ◽  
Biologically Active ◽  
Peptide Sequence ◽  
Target Cells ◽  
Content Type ◽  
Peptide Length

ABSTRACTEscherichia colimicrocin C (McC) consists of a ribosomally synthesized heptapeptide attached to a modified adenosine. McC is actively taken up by sensitiveEscherichia colistrains through the YejABEF transporter. Inside the cell, McC is processed by aminopeptidases, which release nonhydrolyzable aminoacyl adenylate, an inhibitor of aspartyl-tRNA synthetase. McC is synthesized by the MccB enzyme, which terminally adenylates the MccA heptapeptide precursor MRTGNAN. Earlier, McC analogs with shortened peptide lengths were prepared by total chemical synthesis and were shown to have strongly reduced biological activity due to decreased uptake. Variants with longer peptides were difficult to synthesize, however. Here, we used recombinant MccB to prepare and characterize McC-like molecules with altered peptide moieties, including extended peptide lengths. We find that N-terminal extensions ofE. coliMccA heptapeptide do not affect MccB-catalyzed adenylation and that some extended-peptide-length McC analogs show improved biological activity. When the peptide length reaches 20 amino acids, both YejABEF and SbmA can perform facilitated transport of toxic peptide adenylates inside the cell. A C-terminal fusion of the carrier maltose-binding protein (MBP) with the MccA peptide is also recognized by MccBin vivoandin vitro, allowing highly specific adenylation and/or radioactive labeling of cellular proteins.IMPORTANCEEnzymatic adenylation of chemically synthesized peptides allowed us to generate biologically active derivatives of the peptide-nucleotide antibiotic microcin C with improved bioactivity and altered entry routes into target cells, opening the way for development of various McC-based antibacterial compounds not found in nature.

Characteristics of circulating growth hormone in women after acute heavy resistance exercise

2001 ◽  
Vol 281 (4) ◽  
pp. E878-E887 ◽  
Author(s):  
Wesley C. Hymer ◽  
William J. Kraemer ◽  
Bradley C. Nindl ◽  
James O. Marx ◽  
David E. Benson ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Resistance Exercise ◽  
Kidney Diseases ◽  
Chemical Reduction ◽  
Human Growth ◽  
Size Exclusion ◽  
Target Cells ◽  
Diagnostic Systems ◽  
Heavy Resistance Exercise

The effects of exercise on the molecular nature of secreted human growth hormone (GH) or its biological activity are not well understood. Plasma from women (average age 23.6 yr, n = 35), drawn before and after an acute heavy resistance exercise test, was fractionated by size exclusion chromatography into three size classes, namely, >60 kDa ( fraction A), 30–60 kDa ( fraction B), and <30 kDa ( fraction C), before GH assay. Concentrations of GH in these fractions, as well as in unfractioned plasma, were measured by the Nichols immunoradiometric assay, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) polyclonal competitive RIA, Diagnostic Systems Laboratory's immunofunctional assay (measures dimerization-capable species), and the rat tibial bioassay. Significantly increased circulating GH concentrations of two- to fourfold were observed when immunoassays in unfractionated plasma samples were used, but they showed no significant change with use of the rat tibial bioassay. Significant exercise-induced increases in GH were found in fractions B and C but not in fraction A. Because chemical reduction of the samples before GH immunoassay significantly increased GH concentrations in fractions B and C (Nichols and NIDDK kits) after exercise, it is concluded that exercise may specifically increase release of disulfide-linked hormone molecules and/or fragments. Finally, because most of the GH released after exercise was able to dimerize the GH receptor in vitro, it is also concluded that these forms have the two intact binding sites required to initiate signal transduction in target cells.

Modern Biophysical Approaches to Study Protein–Ligand Interactions

2018 ◽  
Vol 13 (04) ◽  
pp. 133-155
Author(s):  
Priyanka Biswas
Keyword(s):  
Single Molecule ◽  
Analytical Ultracentrifugation ◽  
Correlation Spectroscopy ◽  
Titration Calorimetry ◽  
Resonance Fluorescence ◽  
Biological Interactions ◽  
Protein Ligand Interactions ◽  
Dual Polarization Interferometry ◽  
Ligand Interactions

Protein–ligand interactions act as a pivot to the understanding of most of the biological interactions. The study of interactions between proteins and cellular molecules has led to the establishment and identification of various important pathways that control biological systems. Investigators working in different fields of biological sciences have an intrinsic interest in this field and complement their findings by the application of different biophysical approaches and tools to quantify protein–ligand interactions that include protein–small molecules, protein–DNA, protein–RNA, protein–protein both in vitro and in vivo. In this paper, the various biophysical techniques that can be employed to study such interactions will be discussed. In addition to native gel electrophoresis and fluorescence-based methods, more details will be discussed, on the broad range of modern day biophysical tools such as Circular Dichroism, Fourier Transform Infrared (FTIR) Spectroscopy, Isothermal Titration Calorimetry, Analytical Ultracentrifugation, Surface Plasmon Resonance, Fluorescence Correlation Spectroscopy, Differential Scanning Fluorimetry, Nuclear Magnetic Resonance, Mass Spectroscopy, Single Molecule Spectroscopy, Dual Polarization Interferometry, Micro Scale Thermophoresis and Electro–switchable Biosensors that can be used to study the different aspects of protein–ligand interactions.

Phosphorylation of the dimeric cytoplasmic domain of the phytosulfokine receptor, PSKR1

2016 ◽  
Vol 473 (19) ◽  
pp. 3081-3098 ◽  
Author(s):  
Victor Muleya ◽  
Claudius Marondedze ◽  
Janet I. Wheeler ◽  
Ludivine Thomas ◽  
Yee-Fong Mok ◽  
...  
Keyword(s):  
Guanylate Cyclase ◽  
Kinase Activity ◽  
Analytical Ultracentrifugation ◽  
Domain Architecture ◽  
Defense Responses ◽  
Cytoplasmic Domain ◽  
Size Exclusion ◽  
Cyclase Activity ◽  
Guanylate Cyclase Activity

Phytosulfokines (PSKs) are plant peptide hormones that co-regulate plant growth, differentiation and defense responses. PSKs signal through a plasma membrane localized leucine-rich repeat receptor-like kinase (phytosulfokine receptor 1, PSKR1) that also contains a functional cytosolic guanylate cyclase with its cyclase catalytic center embedded within the kinase domain. To functionally characterize this novel type of overlapping dual catalytic function, we investigated the phosphorylation of PSKR1 in vitro. Tandem mass spectrometry of the cytoplasmic domain of PSKR1 (PSKR1cd) revealed at least 11 phosphorylation sites (8 serines, 2 threonines and 1 tyrosine) within the PSKR1cd. Phosphomimetic mutations of three serine residues (Ser686, Ser696 and Ser698) in tandem at the juxta-membrane position resulted in enhanced kinase activity in the on-mutant that was suppressed in the off-mutant, but both mutations reduced guanylate cyclase activity. Both the on and off phosphomimetic mutations of the phosphotyrosine (Tyr888) residue in the activation loop suppressed kinase activity, while neither mutation affected guanylate cyclase activity. Size exclusion and analytical ultracentrifugation analysis of the PSKR1cd suggest that it is reversibly dimeric in solution, which was further confirmed by biflourescence complementation. Taken together, these data suggest that in this novel type of receptor domain architecture, specific phosphorylation and dimerization are possibly essential mechanisms for ligand-mediated catalysis and signaling.

scholarly journals Guanidinium chloride denaturation of the dimeric Bacillus licheniformis BlaI repressor highlights an independent domain unfolding pathway

2004 ◽  
Vol 384 (1) ◽  
pp. 179-190 ◽  
Author(s):  
Christelle VREULS ◽  
Patrice FILÉE ◽  
Hélène VAN MELCKEBEKE ◽  
Tony AERTS ◽  
Peter DE DEYN ◽  
...  
Keyword(s):  
Bacillus Licheniformis ◽  
Analytical Ultracentrifugation ◽  
Cd Spectroscopy ◽  
Size Exclusion ◽  
Cross Linking ◽  
Guanidinium Chloride ◽  
Dimerization Domain ◽  
Terminal Domain ◽  
Equilibrium Unfolding ◽  
Partially Unfolded

The Bacillus licheniformis 749/I BlaI repressor is a prokaryotic regulator that, in the absence of a β-lactam antibiotic, prevents the transcription of the blaP gene, which encodes the BlaP β-lactamase. The BlaI repressor is composed of two structural domains. The 82-residue NTD (N-terminal domain) is a DNA-binding domain, and the CTD (C-terminal domain) containing the next 46 residues is a dimerization domain. Recent studies have shown the existence of the monomeric, dimeric and tetrameric forms of BlaI in solution. In the present study, we analyse the equilibrium unfolding of BlaI in the presence of GdmCl (guanidinium chloride) using different techniques: intrinsic and ANS (8-anilinonaphthalene-l-sulphonic acid) fluorescence, far- and near-UV CD spectroscopy, cross-linking, analytical ultracentrifugation, size exclusion chromatography and NMR spectroscopy. In addition, the intact NTD and CTD were purified after proteolysis of BlaI by papain, and their unfolding by GdmCl was also studied. GdmCl-induced equilibrium unfolding was shown to be fully reversible for BlaI and for the two isolated fragments. The results demonstrate that the NTD and CTD of BlaI fold/unfold independently in a four-step process, with no significant co-operative interactions between them. During the first step, the unfolding of the BlaI CTD occurs, followed in the second step by the formation of an ‘ANS-bound’ intermediate state. Cross-linking and analytical ultracentrifugation experiments suggest that the dissociation of the dimer into two partially unfolded monomers takes place in the third step. Finally, the unfolding of the BlaI NTD occurs at a GdmCl concentration of approx. 4 M. In summary, it is shown that the BlaI CTD is structured, more flexible and less stable than the NTD upon GdmCl denaturation. These results contribute to the characterization of the BlaI dimerization domain (i.e. CTD) involved in the induction process.

scholarly journals The iron–siderophore transporter FhuA is the receptor for the antimicrobial peptide microcin J25: role of the microcin Val11–Pro16 β-hairpin region in the recognition mechanism

2005 ◽  
Vol 389 (3) ◽  
pp. 869-876 ◽  
Author(s):  
Delphine Destoumieux-Garzón ◽  
Sophie Duquesne ◽  
Jean Peduzzi ◽  
Christophe Goulard ◽  
Michel Desmadril ◽  
...  
Keyword(s):  
Antimicrobial Peptide ◽  
Size Exclusion ◽  
Receptor Interaction ◽  
Titration Calorimetry ◽  
Scanning Calorimetry ◽  
Recognition Mechanism ◽  
Microcin J25

The role of the outer-membrane iron transporter FhuA as a potential receptor for the antimicrobial peptide MccJ25 (microcin J25) was studied through a series of in vivo and in vitro experiments. The requirement for both FhuA and the inner-membrane TonB–ExbB–ExbD complex was demonstrated by antibacterial assays using complementation of an fhuA− strain and by using isogenic strains mutated in genes encoding the protein complex respectively. In addition, MccJ25 was shown to block phage T5 infection of Escherichia coli, in vivo, by inhibiting phage adhesion, which suggested that MccJ25 prevents the interaction between the phage and its receptor FhuA. This in vivo activity was confirmed in vitro, as MccJ25 inhibited phage T5 DNA ejection triggered by purified FhuA. Direct interaction of MccJ25 with FhuA was demonstrated for the first time by size-exclusion chromatography and isothermal titration calorimetry. MccJ25 bound to FhuA with a 2:1 stoichiometry and a Kd of 1.2 μM. Taken together, our results demonstrate that FhuA is the receptor for MccJ25 and that the ligand–receptor interaction may occur in the absence of other components of the bacterial membrane. Finally, both differential scanning calorimetry and antimicrobial assays showed that MccJ25 binding involves external loops of FhuA. Unlike native MccJ25, a thermolysin-cleaved MccJ25 variant was unable to bind to FhuA and failed to prevent phage T5 infection of E. coli. Therefore the Val11–Pro16 β-hairpin region of MccJ25, which is disrupted upon cleavage by thermolysin, is required for microcin recognition.

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