Peng C.,Tongji University |
Peng C.,Shanghai JiaoTong University |
Ye M.,Tongji University |
Wang Y.,Tongji University |
And 7 more authors.
Peptides | Year: 2010
Two novel conotoxins from vermivorous cone snails Conus pulicarius and Conus tessulatus, designated as Pu14.1 and ts14a, were identified by cDNA cloning and peptide purification, respectively. The signal sequence of Pu14.1 is identical to that of α-conotoxins, while its predicted mature peptide, pu14a, shares high sequence similarity with ts14a, with only one residue different in their first intercysteine loop, which contains 10 residues and is rich in proline. Both pu14a and ts14a contain four separate cysteines in framework 14 (C-C-C-C). Peptide pu14a was chemically synthesized, air oxidized, and the connectivity of its two disulfide bonds was determined to be C1-C3, C2-C4, which is the same as found in α-conotoxins. The synthetic pu14a induced a sleeping symptom in mice and was toxic to freshwater goldfish upon intramuscular injection. Using the Xenopus oocyte heterologous expression system, 1 μM of pu14a demonstrated to inhibit the rat neuronal α3β2-containing as well as the mouse neuromuscular α1β1γδ subtypes of nicotinic acetylcholine receptors, and then rapidly dissociated from the receptors. However, this toxin had no inhibitory effect on potassium channels in mouse superior cervical ganglion neurons. According to the identical signal sequence to α-conotoxins, the unique cysteine framework and molecular target of pu14a, we propose that pu14a and ts14a may represent a novel subfamily in the A-superfamily, designated as α1-conotoxins. © 2010 Elsevier Inc. All rights reserved.
Kim Y.,Texas A&M University |
Wang X.,Texas A&M University |
Zhang X.-S.,Texas A&M University |
Grigoriu S.,Physiology and Biotechnology |
And 3 more authors.
Environmental Microbiology | Year: 2010
Previously we identified that the Escherichia coli protein MqsR (YgiU) functions as a toxin and that it is involved in the regulation of motility by quorum sensing signal autoinducer-2 (AI-2). Furthermore, MqsR is directly associated with biofilm development and is linked to the development of persister cells. Here we show that MqsR and MqsA (YgiT) are a toxin/antitoxin (TA) pair, which, in significant difference to other TA pairs, regulates additional loci besides its own. We have recently identified that MqsR functions as an RNase. However, using three sets of whole-transcriptome studies and two nickel-enrichment DNA binding microarrays coupled with cell survival studies in which MqsR was overproduced in isogenic mutants, we identified eight genes (cspD, clpX, clpP, lon, yfjZ, relB, relE and hokA) that are involved in a mode of MqsR toxicity in addition to its RNase activity. Quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) showed that (i) the MqsR/MqsA complex (and MqsA alone) represses the toxin gene cspD, (ii) MqsR overproduction induces cspD, (iii) stress induces cspD, and (iv) stress fails to induce cspD when MqsR/MqsA are overproduced or when mqsRA is deleted. Electrophoretic mobility shift assays show that the MqsA/MqsR complex binds the promoter of cspD. In addition, proteases Lon and ClpXP are necessary for MqsR toxicity. Together, these results indicate the MqsR/MqsA complex represses cspD which may be derepressed by titrating MqsA with MqsR or by degrading MqsA via stress conditions through proteases Lon and ClpXP. Hence, we demonstrate that the MqsR/MqsA TA system controls cell physiology via its own toxicity as well as through its regulation of another toxin, CspD. © 2010 Society for Applied Microbiology and Blackwell Publishing Ltd.
Lopez-Fagundo C.,Physiology and Biotechnology |
Lopez-Fagundo C.,Brown University |
Lopez-Fagundo C.,University of Zürich |
Bar-Kochba E.,Brown University |
And 6 more authors.
Journal of the Royal Society Interface | Year: 2014
The mechanical interaction between Schwann cells (SCs) and their microenvironment is crucial for the development, maintenance and repair of the peripheral nervous system. In this paper, we present a detailed investigation on the mechanosensitivity of SCs across a physiologically relevant substrate stiffness range. Contrary to many other cell types, we find that the SC spreading area and cytoskeletal actin architecture were relatively insensitive to substrate stiffness with pronounced stress fibre formation across all moduli tested (0.24-4.80 kPa). Consistent with the presence of stress fibres, we found that SCs generated large surface tractions on stiff substrates and large, finite material deformations on soft substrates. When quantifying the three-dimensional characteristics of the SC traction profiles,we observed a significant contribution from the out-of-plane traction component, locally giving rise to rotational moments similar to those observed in mesenchymal embryonic fibroblasts. Taken together, these measurements provide the first set of quantitative biophysical metrics of howSCs interact with their physical microenvironment, which are anticipated to aid in the development of tissue engineering scaffolds designed to promote functional integration of SCs into post-injury in vivo environments. © 2014 The Author(s) Published by the Royal Society.
Achilli T.-M.,Physiology and Biotechnology |
Achilli T.-M.,Center for Biomedical Engineering |
McCalla S.,Center for Biomedical Engineering |
McCalla S.,Brown University |
And 6 more authors.
Molecular Pharmaceutics | Year: 2014
There is a need for new quantitative in vitro models of drug uptake and diffusion to help assess drug toxicity/efficacy as well as new more predictive models for drug discovery. We report a three-dimensional (3D) multilayer spheroid model and a new algorithm to quantitatively study uptake and inward diffusion of fluorescent calcein via gap junction intercellular communication (GJIC). When incubated with calcein-AM, a substrate of the efflux transporter P-glycoprotein (Pgp), spheroids from a variety of cell types accumulated calcein over time. Accumulation decreased in spheroids overexpressing Pgp (HEK-MDR) and was increased in the presence of Pgp inhibitors (verapamil, loperamide, cyclosporin A). Inward diffusion of calcein was negligible in spheroids that lacked GJIC (OVCAR-3, SK-OV-3) and was reduced in the presence of an inhibitor of GJIC (carbenoxolone). In addition to inhibiting Pgp, verapamil and loperamide, but not cyclosporin A, inhibited inward diffusion of calcein, suggesting that they also inhibit GJIC. The dose response curves of verapamils inhibition of Pgp and GJIC were similar (IC50: 8 μM). The method is amenable to many different cell types and may serve as a quantitative 3D model that more accurately replicates in vivo barriers to drug uptake and diffusion. © 2014 American Chemical Society.
Helou Y.A.,Physiology and Biotechnology |
Petrashen A.P.,Brown University |
Salomon A.R.,Brown University
Journal of Proteome Research | Year: 2015
Vav1, a Rac/Rho guanine nucleotide exchange factor and a critical component of the T-cell receptor (TCR) signaling cascade is tyrosine phosphorylated rapidly in response to T-cell activation. Vav1 has established roles in proliferation, cytokine secretion, Ca2+ responses, and actin cytoskeleton regulation; however, its function in the regulation of phosphorylation of TCR components, including the ζ chain, the CD3 δ, ε, γ chains, and the associated kinases Lck and ZAP-70, is not well established. To obtain a more comprehensive picture of the role of Vav1 in receptor proximal signaling, we performed a wide-scale characterization of Vav1-dependent tyrosine phosphorylation events using quantitative phosphoproteomic analysis of Vav1-deficient T cells across a time course of TCR stimulation. Importantly, this study revealed a new function for Vav1 in the negative feedback regulation of the phosphorylation of immunoreceptor tyrosine-based activation motifs within the ζ chains, CD3 δ, ε, γ chains, as well as activation sites on the critical T cell tyrosine kinases Itk, Lck, and ZAP-70. Our study also uncovered a previously unappreciated role for Vav1 in crosstalk between the CD28 and TCR signaling pathways. © 2015 American Chemical Society.
PubMed | Physiology and Biotechnology.
Type: Journal Article | Journal: BioTechniques | Year: 2016
Hundreds of commercially available fluorescent dyes are used to quantify a wide range of biological functions of cells in culture, and their use has been a mainstay of basic research, toxicity testing, and drug discovery. However, nearly all of these dyes have been optimized for use on cells cultured as two-dimensional monolayers. Three-dimensional culture systems more accurately recapitulate native tissues, but their size and complexity present a new set of challenges for the use of fluorescent dyes, especially with regards to accurate quantitation. We determined the most accurate method to quantify fluorescence as a function of whether cells were uniformly labeled with dye prior to spheroid formation or if the dye was diffused into the spheroid after its formation. Using multicellular spheroids labeled with calcein-AM via these two different staining methods, we performed time-lapse fluorescence microscopy. For uniformly labeled spheroids, fluorescence was best normalized to volume, whereas for spheroids labeled via dye diffusion, fluorescence was best normalized to surface area. This framework for evaluating dyes can easily be extended to other applications. Utilizing the appropriate size-based normalization strategy enhanced our ability to detect statistically significant differences between experimental conditions.
PubMed | Physiology and Biotechnology.
Type: Journal Article | Journal: The Journal of biological chemistry | Year: 2013
Mitogen-activated protein kinases (MAPKs) fulfill essential biological functions and are key pharmaceutical targets. Regulation of MAPKs is achieved via a plethora of regulatory proteins including activating MAPKKs and an abundance of deactivating phosphatases. Although all regulatory proteins use an identical interaction site on MAPKs, the common docking and hydrophobic pocket, they use distinct kinase interaction motif (KIM or D-motif) sequences that are present in linear, peptide-like, or well folded protein domains. It has been recently shown that a KIM-containing MAPK-specific dual specificity phosphatase DUSP10 uses a unique binding mode to interact with p38. Here we describe the interaction of the MAPK binding domain of DUSP16 with p38 and show that despite belonging to the same dual specificity phosphatase (DUSP) family, its interaction mode differs from that of DUSP10. Indeed, the DUSP16 MAPK binding domain uses an additional helix, -helix 4, to further engage p38. This leads to an additional interaction surface on p38. Together, these structural and energetic differences in p38 engagement highlight the fine-tuning necessary to achieve MAPK specificity and regulation among multiple regulatory proteins.