The C-terminal extension of VgrG4 from Klebsiella pneumoniae remodels host cell microfilaments.

Klebsiella pneumoniae is an opportunistic pathogen, which concerns public health systems worldwide, as multiple antibiotic-resistant strains are frequent. One of its pathogenicity factors is the Type VI Secretion System (T6SS), a macromolecular complex assembled through the bacterial membranes. T6SS injects effector proteins inside target cells. Such effectors confer competitive advantages or modulate the target cell signaling and metabolism to favor bacterial infection. The VgrG protein is a T6SS core component. It may present a variable C-terminal domain carrying an additional effector function. Kp52.145 genome encodes three VgrG proteins, one of them with a C-terminal extension (VgrG4-CTD). VgrG4-CTD is 138 amino acids long, does not contain domains of known function, but is conserved in some Klebsiella, and non-Klebsiella species. To get insights into its function, recombinant VgrG4-CTD was used in pulldown experiments to capture ligands from macrophages and lung epithelial cells. A total of 254 proteins were identified: most of them are ribosomal proteins. Cytoskeleton-associated and proteins involved in the phagosome maturation pathway were also identified. We further showed that VgrG4-CTD binds actin and induces actin remodeling in macrophages. This study presents novel clues on the role of K. pneumoniae T6SS in pathogenesis.

Automated structure modeling of large protein assemblies using crosslinks as distance restraints.

Crosslinking mass spectrometry is increasingly used for structural characterization of multisubunit protein complexes. Chemical crosslinking captures conformational heterogeneity, which typically results in conflicting crosslinks that cannot be satisfied in a single model, making detailed modeling a challenging task. Here we introduce an automated modeling method dedicated to large protein assemblies ('XL-MOD' software is available at http://aria.pasteur.fr/supplementary-data/x-links) that (i) uses a form of spatial restraints that realistically reflects the distribution of experimentally observed crosslinked distances; (ii) automatically deals with ambiguous and/or conflicting crosslinks and identifies alternative conformations within a Bayesian framework; and (iii) allows subunit structures to be flexible during conformational sampling. We demonstrate our method by testing it on known structures and available crosslinking data. We also crosslinked and modeled the 17-subunit yeast RNA polymerase III at atomic resolution; the resulting model agrees remarkably well with recently published cryoelectron microscopy structures and provides additional insights into the polymerase structure.

Exploring the unbinding of Leishmania (L.) amazonensis CPB derived-epitopes from H2 MHC class I proteins.

New strategies to control Leishmania disease demand an extensive knowledge about several aspects of infection including the understanding of its molecular events. In murine models, cysteine proteinase B from Leishmania amazonensis promotes regulation of immune response, and fragments from its C-terminus extension (cyspep) can play a decisive role in the host-parasite interaction. The interaction between cyspep-derived peptides and major histocompatibility complex (MHC) proteins is a crucial factor in Leishmania infections. Seven cyspep-derived peptides, previously identified as capable of interacting with H-2 (murine) MHC class I proteins, were studied in this work. We established a protocol to simulate the unbinding of these peptides from the cleft of H-2 receptors. From the simulations, we estimated the corresponding free energy of dissociation (ΔGd ) and described the molecular events that occur during the exit of peptides from the cleft. To test the reliability of this method, we first applied it to a calibration set of four crystallographic MHC/peptide complexes. Next, we explored the unbinding of the seven complexes mentioned above. Results were consistent with ΔGd values obtained from surface plasmon resonance (SPR) experiments. We also identified some of the primary interactions between peptides and H-2 receptors, and we detected three regions of influence for the interaction. This pattern was systematically observed for the peptides and helped determine a minimum distance for the real interaction between peptides and H-2 proteins occurring at ∼ 25 Å.

Gedunin Binds to Myeloid Differentiation Protein 2 and Impairs Lipopolysaccharide-Induced Toll-Like Receptor 4 Signaling in Macrophages.

Recognition of bacterial lipopolysaccharide (LPS) by innate immune system is mediated by the cluster of differentiation 14/Toll-like receptor 4/myeloid differentiation protein 2 (MD-2) complex. In this study, we investigated the modulatory effect of gedunin, a limonoid from species of the Meliaceae family described as a heat shock protein Hsp90 inhibitor, on LPS-induced response in immortalized murine macrophages. The pretreatment of wild-type (WT) macrophages with gedunin (0.01-100 µM, noncytotoxic concentrations) inhibited LPS (50 ng/ml)-induced calcium influx, tumor necrosis factor-α, and nitric oxide production in a concentration-dependent manner. The selective effect of gedunin on MyD88-adapter-like/myeloid differentiation primary response 88- and TRIF-related adaptor molecule/TIR domain-containing adapter-inducing interferon-ß-dependent signaling pathways was further investigated. The pretreatment of WT, TIR domain-containing adapter-inducing interferon-ß knockout, and MyD88 adapter-like knockout macrophages with gedunin (10 µM) significantly inhibited LPS (50 ng/ml)-induced tumor necrosis factor-α and interleukin-6 production, at 6 hours and 24 hours, suggesting that gedunin modulates a common event between both signaling pathways. Furthermore, gedunin (10 µM) inhibited LPS-induced prostaglandin E2 production, cyclooxygenase-2 expression, and nuclear factor κB translocation into the nucleus of WT macrophages, demonstrating a wide-range effect of this chemical compound. In addition to the ability to inhibit LPS-induced proinflammatory mediators, gedunin also triggered anti-inflammatory factors interleukin-10, heme oxygenase-1, and Hsp70 in macrophages stimulated or not with LPS. In silico modeling studies revealed that gedunin efficiently docked into the MD-2 LPS binding site, a phenomenon further confirmed by surface plasmon resonance. Our results reveal that, in addition to Hsp90 modulation, gedunin acts as a competitive inhibitor of LPS, blocking the formation of the Toll-like receptor 4/MD-2/LPS complex.

Molecular mechanism of cellulose depolymerization by the two-domain BlCel9A enzyme from the glycoside hydrolase family 9.

Carbohydrate-active enzymes from the glycoside hydrolase family 9 (GH9) play a key role in processing lignocellulosic biomass. Although the structural features of some GH9 enzymes are known, the molecular mechanisms that drive their interactions with cellulosic substrates remain unclear. To investigate the molecular mechanisms that the two-domain Bacillus licheniformis BlCel9A enzyme utilizes to depolymerize cellulosic substrates, we used a combination of biochemical assays, X-ray crystallography, small-angle X-ray scattering, and molecular dynamics simulations. The results reveal that BlCel9A breaks down cellulosic substrates, releasing cellobiose and glucose as the major products, but is highly inefficient in cleaving oligosaccharides shorter than cellotetraose. In addition, fungal lytic polysaccharide oxygenase (LPMO) TtLPMO9H enhances depolymerization of crystalline cellulose by BlCel9A, while exhibiting minimal impact on amorphous cellulose. The crystal structures of BlCel9A in both apo form and bound to cellotriose and cellohexaose were elucidated, unveiling the interactions of BlCel9A with the ligands and their contribution to substrate binding and products release. MD simulation analysis reveals that BlCel9A exhibits higher interdomain flexibility under acidic conditions, and SAXS experiments indicate that the enzyme flexibility is induced by pH and/or temperature. Our findings provide new insights into BlCel9A substrate specificity and binding, and synergy with the LPMOs.

Perillyl Alcohol Promotes Relaxation in Human Umbilical Artery.

BACKGROUND: Perillyl alcohol (POH) is a monoterpenoid found in plant essential oils and has been shown to relax murine vessels, but its effect on human vessels remains poorly studied. OBJECTIVE: The study aimed to characterize the effect of POH on human umbilical arteries (HUA). METHODS: Rings of HUA were obtained from uncomplicated patients and suspended in an organ bath for isometric recording. The vasorelaxant effect of POH in HUA was evaluated on basal tone and electromechanical or pharmacomechanical contractions, and possible mechanisms of action were also investigated. RESULTS: POH (1-1000 µM) altered the basal tone of HUA and completely relaxed HUA rings precontracted with KCl (60 mM) or 5-HT (10 µM), obtaining greater potency in the pharmacomechanical pathway (EC50 110.1 µM), suggesting a complex interference in the mobilization of extra- and intracellular Ca2+. POH (1000 µM) inhibited contractions induced by BaCl2 (0.1-30 mM) in a similar way to nifedipine (10 µM), indicating a possible blockade of L-type VOCC. In the presence of potassium channel blockers, tetraethylammonium (1 mM), 4-aminopyridine (1 mM), or glibenclamide (10 µM), an increase in the EC50 value of the POH was observed, suggesting a modulation of the activity of BKCa, KV, and KATP channels. CONCLUSION: The data from this study suggest that POH modulates Ca2+ and K+ ion channels to induce a relaxant response in HUA.

Vasorelaxant effect of phenylpropanoids: Methyl eugenol and eugenol in human umbilical cord vein.

Methyl-eugenol (ME) and eugenol (EUG) are phenylpropanoids with vasodilatory effects. While EUG's vasorelaxant effect in human umbilical artery (HUA) is known, their action in veins is unclear. This study aimed to evaluate ME and EUG in human umbilical vein (HUV). Isolated HUV underwent tension recordings. ME and EUG caused 100 % relaxation in HUV, with EC50 values corresponding to: 174.3 ± 7.3 and 217.3 ± 6.2 µM for ME and EUG respectively in presence of K+; 362.3 ± 5.4 and 227.7 ± 4.9 µM for ME and EUG respectively and in presence of serotonin (5-HT). It was observed that in presence of BaCl2 and CaCl2 evoked contractions, ME (800 and 1000 µM) and EUG (1000 and 1400 µM) prevent the contractions. In presence of K+ channel blockers it was observed that ME promoted relaxation compared to its control, except in presence of 4-AP, suggesting a possible Ca2+-dependent K+ channel activation for this molecule; EUG increased all EC50 in presence of the K+ blockers except in presence of TEA 1 mM. Greater pharmacological potency was observed for ME. This study highlights natural substances' effects on HUV contractile parameters, suggesting ME and EUG as potential vasodilators in maintaining fetal oxygenation and venous flow during gestational hypertensive syndromes.

Vasodilation promoted by (E,E)-farnesol involving ion channels in human umbilical arteries.

Background: (E,E)-farnesol is a sesquiterpene alcohol derived from plants and animals that exhibits pharmacological properties in the cardiovascular system. However, its effects on human umbilical vessels remain unknown. Purpose: Thus, this study aims to characterize the vasodilatory effect of (E,E)-farnesol in human umbilical arteries (HUA). Study design: The tissue is obtained from pregnant women over 18 years of age, normotensive, and without prepartum complications. After collected, the tissue was segmented and dissected to remove Wharton's jelly and obtain the umbilical arteries segments. Methods: HUA segments were isolated and sectioned into rings that were subjected to isometric tension recordings in an organ bath. Results: (E,E)-farnesol (1 µmol/L to 1 mmol/L) promoted vasodilatory effect in HUA preparations, affecting basal tone, and inhibiting the electromechanical coupling induced by KCl 60 mmol/L with greater potency (EC50 225.3 µmol/L) than the pharmacomechanical coupling induced by 5-HT 10 µmol/L (EC50 363.5 µmol/L). In the absence of extracellular calcium, pharmacomechanical coupling was also abolished, and contractions induced by CaCl2 or BaCl2 were attenuated by (E,E)-farnesol indicating a possible direct inhibition of L-type VOCC as a mechanism of the vasodilatory effect. The vasodilator efficacy of (E,E)-farnesol on reduction of vasocontraction induced by the presence of tetraethylammonium (1 or 10 mmol/L), 4-aminopyridine (1 mmol/L) and glibenclamide (10 µmol/L) suggesting a possible influence of different potassium channels (BKCa, KV and KATP). Conclusion: These results suggest that (E,E)-farnesol may be a promising pharmacological candidate for obstetric hypertensive disorders.

Vasorelaxant effect of (E,E)-farnesol in human umbilical vein ex vivo assays.

(E,E)-farnesol is a sesquiterpene acyclic alcohol produced by bacteria, protozoa, fungi, plants, and animals. The literature describes its applications in food, pharmaceutical, and cosmetic industries, and also in the pharmacological context with a vasorelaxant effect. However, its effects on human umbilical vessels remain poorly investigated. Thus, this study aims to investigate, in a new way, the vasorelaxant effect of (E,E)-farnesol in human umbilical veins (HUV) from healthy donors. Rings obtained from isolated HUV were suspended in an organ bath to record their isometric tension in different experimental sections. (E,E)-farnesol (1 µmol/L to 1 mmol/L) promoted vasorelaxant effect in venous preparations contracted by depolarization (KCl 60 mmol/L) or pharmacological agonism (5-HT 10 µmol/L), with EC50 values of 239.9 µmol/L and 424 µmol/L, respectively. In calcium-free solution, this effect was also observable. (E,E)-farnesol was able to suppress contractions evoked by CaCl2 and BaCl2 suggesting a blockade of voltage-dependent (especially L-type) calcium channels. The vasorelaxant efficacy and potency of (E,E)-farnesol were affected in the presence of tetraethylammonium (1 and 10 mmol/L), glibenclamide (10 µmol/L) and BaCl2 (1 mmol/L) indicating a possible involvement of potassium channels (BKCa, KATP and KIR) in this effect. Our data suggest that (E,E)-farnesol has a promising potential to be applicable as a vasodilator in hypertensive conditions in pregnancy that alter HUV reactivity.

Possible mechanisms involved in the neuroprotective effect of Trans,trans-farnesol on pilocarpine-induced seizures in mice.

This study aimed to investigate, through in vivo and in vitro methodologies, the effect of acute trans,trans-farnesol (12.5, 25, 50 or 100 mg/kg, p.o.) administration on behavioral and neurochemical parameters associated with pilocarpine-induced epileptic seizure (300 mg/kg, i.p.) in mice. The initial results showed that the compound in question presents no anxiolytic-like or myorelaxant effects, despite reducing locomotor activity in the animals at all doses tested. In addition, the lowest dose increased the latency to onset of the first epileptic seizure, and the time to death. In addition to decreasing the mortality percentage in mice submitted to the pilocarpine model. In this same model, pretreatment with the lowest dose of the compound decreased the hippocampal concentrations of thiobarbituric acid and nitrite, and partially restored striatal concentrations of noradrenaline, dopamine, and serotonin. Taken together, the results suggest that trans,trans-farnesol presents a central depressant effect which contributes to its antiepileptic action which, in turn, seems to be mediated by the antagonism of muscarinic cholinergic receptors, reduction of oxidative stress. and modulation of noradrenaline, dopamine and serotonin concentrations in the central nervous system.

High temperatures enhance cooperative motions between CBM and catalytic domains of a thermostable cellulase: mechanism insights from essential dynamics.

Cellulases from thermophiles are capable of cleaving sugar chains from cellulose efficiently at high temperatures. The thermo-resistant Cel9A-68 cellulase possesses two important domains: CBM and a catalytic domain connected by a Pro/Ser/Thr rich linker. These domains act cooperatively to allow efficient catalysis. Despite exhaustive efforts to characterize cellulase binding and mechanism of action, a detailed description of the cellulose intrinsic flexibility is still lacking. From computational simulations we studied the temperature influence on the enzyme plasticity, prior to substrate binding. Interestingly, we observed an enhancement of collective motions at high temperatures. These motions are the most representative and describe an intrinsic hinge bending transition. A detailed analysis of these motions revealed an interdomain approximation where D459 and G460, located at the linker region, are the hinge residues. Therefore, we propose a new putative site for mutagenesis targeting the modulation of such conformational transition that may be crucial for activity.

Consensus modes, a robust description of protein collective motions from multiple-minima normal mode analysis--application to the HIV-1 protease.

Protein flexibility is essential for enzymatic function, ligand binding, and protein-protein or protein-nucleic acid interactions. Normal mode analysis has increasingly been shown to be well suited for studying such flexibility, as it can be used to identify favorable structural deformations that correspond to functional motions. However, normal modes are strictly relevant to a single structure, reflecting a particular minimum on a complex energy surface, and are thus susceptible to artifacts. We describe a new theoretical framework for determining "consensus" normal modes from a set of related structures, such as those issuing from a short molecular dynamics simulation. This approach is more robust than standard normal mode analysis, and provides higher collectivity and symmetry properties. In an application to HIV-1 protease, the low-frequency consensus modes describe biologically relevant motions including flap opening and closing that can be used in interpreting structural changes accompanying the binding of widely differing inhibitors.

Glycosylation effects on the structure and dynamics of a full-length Cel7A cellulase.

Fungi cellulases are used to degrade cellulose-containing biomass for bioethanol production. Industrial cellulases such as Cel7A from Trichoderma reesei (TrCel7A) are critical in this process. Thus, the understanding of structure and dynamics is crucial for engineering variants with improved cellulolytic activity. This cellulase consists of two domains connected by a flexible and highly glycosylated linker. However, the linker flexibility has hindered the determination of Cel7A complete structure. Herein, based on atomic and sparse data, we applied integrative modelling to build a model of the complete enzyme structure. Next, through simulations, we studied the glycosylation effects on the structure and dynamics of a solubilized TrCel7A. Essential dynamics analysis showed that O-glycosylation in the linker led to the stabilization of protein overall dynamics. O-linked glycans seem to restrict protein dihedral angles distribution in this region, selecting more elongated conformations. Besides the reduced flexibility, functional interdomain motions occurred in a more concerted way in the glycosylated system. In contrast, in the absence of glycosylation, we observed vast conformational plasticity with the functional domains frequently collapsing. We report here evidence that targeting Cel7A linker flexibility by point mutations including modification of glycosylation sites could be a promising design strategy to improve cellulase activity.

Gallic acid modulates phenotypic behavior and gene expression in oral squamous cell carcinoma cells by interfering with leptin pathway.

Gallic acid is a polyphenolic compost appointed to interfere with neoplastic cells behavior. Evidence suggests an important role of leptin in carcinogenesis pathways, inducing a proliferative phenotype. We investigated the potential of gallic acid to modulate leptin-induced cell proliferation and migration of oral squamous cell carcinoma cell lines. The gallic acid effect on leptin secretion by oral squamous cell carcinoma cells, as well as the underlying molecular mechanisms, was also assessed. For this, we performed proliferation, migration, immunocytochemical and qPCR assays. The expression levels of cell migration-related genes (MMP2, MMP9, Col1A1, and E-cadherin), angiogenesis (HIF-1α, mir210), leptin signaling (LepR, p44/42 MAPK), apoptosis (casp-3), and secreted leptin levels by oral squamous cell carcinoma cells were also measured. Gallic acid decreased proliferation and migration of leptin-treated oral squamous cell carcinoma cells, and reduced mRNA expression of MMP2, MMP9, Col1A1, mir210, but did not change HIF-1α. Gallic acid decreased levels of leptin secreted by oral squamous cell carcinoma cells, accordingly with downregulation of p44/42 MAPK expression. Thus, gallic acid appears to break down neoplastic phenotype of oral squamous cell carcinoma cells by interfering with leptin pathway.

Molecular dynamics simulations of peptide inhibitors complexed with Trypanosoma cruzi trypanothione reductase.

The drugs against tropical neglected diseases, especially Chagas' Disease, were launched more than 30 years ago, and the development of resistance requires the discovery of new and more effective chemotherapeutic agents. Trypanosoma cruzi has a redox enzyme called trypanothione reductase which was successfully inhibited for peptide derivatives (McKie et al., Amino Acids, 2001, 20: 145). This work aims at studying the mechanism of inhibition of this enzyme through molecular dynamics simulations and evaluating the behavior of some derivatives when inhibiting this protein. We should affirm that any particular molecular dynamics analysis tools (Hbond pattern, 3-D root-mean-square deviation, solvent accessible surface area, etc.) cannot be used apart from the others to justify completely these peptides inhibitory patterns. Based on our results, we reproduced the experimental data and, moreover, we discriminated against a new site in enzyme aperture, which can assist the development of powerful inhibitors against trypanothione reductase enzyme.