RESUMO
A complete understanding of how exposure to environmental substances promotes cancer formation is lacking. More than 70 years ago, tumorigenesis was proposed to occur in a two-step process: an initiating step that induces mutations in healthy cells, followed by a promoter step that triggers cancer development1. Here we propose that environmental particulate matter measuring ≤2.5 µm (PM2.5), known to be associated with lung cancer risk, promotes lung cancer by acting on cells that harbour pre-existing oncogenic mutations in healthy lung tissue. Focusing on EGFR-driven lung cancer, which is more common in never-smokers or light smokers, we found a significant association between PM2.5 levels and the incidence of lung cancer for 32,957 EGFR-driven lung cancer cases in four within-country cohorts. Functional mouse models revealed that air pollutants cause an influx of macrophages into the lung and release of interleukin-1ß. This process results in a progenitor-like cell state within EGFR mutant lung alveolar type II epithelial cells that fuels tumorigenesis. Ultradeep mutational profiling of histologically normal lung tissue from 295 individuals across 3 clinical cohorts revealed oncogenic EGFR and KRAS driver mutations in 18% and 53% of healthy tissue samples, respectively. These findings collectively support a tumour-promoting role for PM2.5 air pollutants and provide impetus for public health policy initiatives to address air pollution to reduce disease burden.
Assuntos
Adenocarcinoma de Pulmão , Poluentes Atmosféricos , Poluição do Ar , Transformação Celular Neoplásica , Neoplasias Pulmonares , Animais , Camundongos , Adenocarcinoma de Pulmão/induzido quimicamente , Adenocarcinoma de Pulmão/genética , Poluentes Atmosféricos/efeitos adversos , Poluentes Atmosféricos/análise , Poluição do Ar/efeitos adversos , Poluição do Ar/análise , Transformação Celular Neoplásica/induzido quimicamente , Transformação Celular Neoplásica/efeitos dos fármacos , Transformação Celular Neoplásica/genética , Exposição Ambiental , Receptores ErbB/genética , Neoplasias Pulmonares/induzido quimicamente , Neoplasias Pulmonares/genética , Material Particulado/efeitos adversos , Material Particulado/análise , Tamanho da Partícula , Estudos de Coortes , Macrófagos Alveolares/efeitos dos fármacos , Células Epiteliais Alveolares/efeitos dos fármacos , Células Epiteliais Alveolares/patologiaRESUMO
The αß T-cell coreceptor CD4 enhances immune responses more than 1 million-fold in some assays, and yet the affinity of CD4 for its ligand, peptide-major histocompatibility class II (pMHC II) on antigen-presenting cells, is so weak that it was previously unquantifiable. Here, we report that a soluble form of CD4 failed to bind detectably to pMHC II in surface plasmon resonance-based assays, establishing a new upper limit for the solution affinity at 2.5 mM. However, when presented multivalently on magnetic beads, soluble CD4 bound pMHC II-expressing B cells, confirming that it is active and allowing mapping of the native coreceptor binding site on pMHC II. Whereas binding was undetectable in solution, the affinity of the CD4/pMHC II interaction could be measured in 2D using CD4- and adhesion molecule-functionalized, supported lipid bilayers, yielding a 2D Kd of â¼5,000 molecules/µm(2) This value is two to three orders of magnitude higher than previously measured 2D Kd values for interacting leukocyte surface proteins. Calculations indicated, however, that CD4/pMHC II binding would increase rates of T-cell receptor (TCR) complex phosphorylation by threefold via the recruitment of Lck, with only a small, 2-20% increase in the effective affinity of the TCR for pMHC II. The affinity of CD4/pMHC II therefore seems to be set at a value that increases T-cell sensitivity by enhancing phosphorylation, without compromising ligand discrimination.
Assuntos
Antígenos CD4/química , Antígeno HLA-A24/química , Cadeias HLA-DRB1/química , Sítios de Ligação , Antígenos CD4/metabolismo , Células HEK293 , Antígeno HLA-A24/metabolismo , Cadeias HLA-DRB1/metabolismo , Humanos , Proteínas Ligantes de Maltose/química , Modelos Moleculares , Fosforilação , Ligação Proteica , Domínios e Motivos de Interação entre Proteínas , Mapeamento de Interação de Proteínas , Processamento de Proteína Pós-Traducional , Estabilidade Proteica , Ressonância de Plasmônio de SuperfícieRESUMO
It has been reported that Pd-Au bimetallic catalysts display improved catalytic performance after adequate calcination. In this study, a model catalyst study was conducted to investigate the effects of annealing in oxygen on the surface structures of Pd-Au alloys by comparing the physicochemical properties of Pd/Au(111) surfaces that were annealed in ultrahigh vacuum (UHV) versus in an oxygen ambient. Auger electron spectroscopy (AES) and Basin hopping simulations reveal that the presence of oxygen can inhibit the diffusion of surface Pd atoms into the subsurface of the Au(111) sample. Reflection-absorption infrared spectroscopy using CO as a probe molecule (CO-RAIRS) and King-Wells measurements of O2 uptake suggest that surfaces annealed in an oxygen ambient possess more contiguous Pd sites than surfaces annealed under UHV conditions. The oxygen-annealed Pd/Au(111) surface exhibited a higher activity for CO oxidation in reactive molecular beam scattering (RMBS) experiments. This enhanced activity likely results from the higher oxygen uptake and relatively facile dissociation of oxygen admolecules due to stronger adsorbate-surface interactions as suggested by temperature-programmed desorption (TPD) measurements. These observations provide fundamental insights into the surface phenomena of Pd-Au alloys, which may prove beneficial in the design of future Pd-Au catalysts.
RESUMO
Gold catalysts display high activity and good selectivity for partial oxidation of a number of alcohol species. In this work, we discuss the effects of oxygen adatoms and surface hydroxyls on the selectivity for oxidation of allylic alcohols (allyl alcohol and crotyl alcohol) on gold surfaces. Utilizing temperature programmed desorption (TPD), reactive molecular beam scattering (RMBS), and density functional theory (DFT) techniques, we provide evidence to suggest that the selectivity displayed towards partial oxidation versus combustion pathways is dependent on the type of oxidant species present on the gold surface. TPD and RMBS results suggest that surface hydroxyls promote partial oxidation of allylic alcohols to their corresponding aldehydes with very high selectivity, while oxygen adatoms promote both partial oxidation and combustion pathways. DFT calculations indicate that oxygen adatoms can react with acrolein to promote the formation of a bidentate surface intermediate, similar to structures that have been shown to decompose to generate combustion products over other transition metal surfaces. Surface hydroxyls do not readily promote such a process. Our results help explain phenomena observed in previous studies and may prove useful in the design of future catalysts for partial oxidation of alcohols.
RESUMO
PD-1, a receptor expressed by T cells, B cells, and monocytes, is a potent regulator of immune responses and a promising therapeutic target. The structure and interactions of human PD-1 are, however, incompletely characterized. We present the solution nuclear magnetic resonance (NMR)-based structure of the human PD-1 extracellular region and detailed analyses of its interactions with its ligands, PD-L1 and PD-L2. PD-1 has typical immunoglobulin superfamily topology but differs at the edge of the GFCC' sheet, which is flexible and completely lacks a C" strand. Changes in PD-1 backbone NMR signals induced by ligand binding suggest that, whereas binding is centered on the GFCC' sheet, PD-1 is engaged by its two ligands differently and in ways incompletely explained by crystal structures of mouse PD-1 · ligand complexes. The affinities of these interactions and that of PD-L1 with the costimulatory protein B7-1, measured using surface plasmon resonance, are significantly weaker than expected. The 3-4-fold greater affinity of PD-L2 versus PD-L1 for human PD-1 is principally due to the 3-fold smaller dissociation rate for PD-L2 binding. Isothermal titration calorimetry revealed that the PD-1/PD-L1 interaction is entropically driven, whereas PD-1/PD-L2 binding has a large enthalpic component. Mathematical simulations based on the biophysical data and quantitative expression data suggest an unexpectedly limited contribution of PD-L2 to PD-1 ligation during interactions of activated T cells with antigen-presenting cells. These findings provide a rigorous structural and biophysical framework for interpreting the important functions of PD-1 and reveal that potent inhibitory signaling can be initiated by weakly interacting receptors.
Assuntos
Células Apresentadoras de Antígenos , Antígeno B7-H1 , Comunicação Celular , Proteína 2 Ligante de Morte Celular Programada 1 , Receptor de Morte Celular Programada 1 , Linfócitos T , Animais , Células Apresentadoras de Antígenos/química , Células Apresentadoras de Antígenos/imunologia , Células Apresentadoras de Antígenos/metabolismo , Antígeno B7-1/química , Antígeno B7-1/genética , Antígeno B7-1/imunologia , Antígeno B7-1/metabolismo , Antígeno B7-H1/química , Antígeno B7-H1/genética , Antígeno B7-H1/imunologia , Antígeno B7-H1/metabolismo , Comunicação Celular/imunologia , Humanos , Camundongos , Modelos Imunológicos , Ressonância Magnética Nuclear Biomolecular , Proteína 2 Ligante de Morte Celular Programada 1/química , Proteína 2 Ligante de Morte Celular Programada 1/genética , Proteína 2 Ligante de Morte Celular Programada 1/imunologia , Proteína 2 Ligante de Morte Celular Programada 1/metabolismo , Receptor de Morte Celular Programada 1/química , Receptor de Morte Celular Programada 1/genética , Receptor de Morte Celular Programada 1/imunologia , Receptor de Morte Celular Programada 1/metabolismo , Ligação Proteica , Estrutura Secundária de Proteína , Relação Estrutura-Atividade , Ressonância de Plasmônio de Superfície , Linfócitos T/química , Linfócitos T/imunologia , Linfócitos T/metabolismoRESUMO
Partial oxidation of alcohols is a topic of great interest in the field of gold catalysis. In this work, we provide evidence that the partial oxidation of allyl alcohol to its corresponding aldehyde, acrolein, over oxygen-precovered gold surfaces occurs via multiple reaction pathways. Utilizing temperature-programmed desorption (TPD) with isotopically labeled water and oxygen species, reactive molecular beam scattering, and density functional theory (DFT) calculations, we demonstrate that the reaction mechanism for allyl alcohol oxidation is influenced by the relative proportions of atomic oxygen and hydroxyl species on the gold surface. Both atomic oxygen and hydroxyl species are shown to be active for allyl alcohol oxidation, but each displays a different pathway of oxidation, as indicated by TPD measurements and DFT calculations. The hydroxyl hydrogen of allyl alcohol is readily abstracted by either oxygen adatoms or adsorbed hydroxyl species on the gold surface to generate a surface-bound allyloxide intermediate, which then undergoes α-dehydrogenation via interaction with an oxygen adatom or surface hydroxyl species to generate acrolein. Mediation of a second allyloxide with the hydroxyl species lowers the activation barrier for the α-dehydrogenation process. A third pathway exists in which two hydroxyl species recombine to generate water and an oxygen adatom, which subsequently dehydrogenates allyloxide. This work may aid in the understanding of oxidative catalysis over gold and the effect of water therein.
RESUMO
Native and non-native ligands of the T cell receptor (TCR), including antibodies, have been proposed to induce signaling in T cells via intra- or intersubunit conformational rearrangements within the extracellular regions of TCR complexes. We have investigated whether any signatures can be found for such postulated structural changes during TCR triggering induced by antibodies, using crystallographic and mutagenesis-based approaches. The crystal structure of murine CD3ε complexed with the mitogenic anti-CD3ε antibody 2C11 enabled the first direct structural comparisons of antibody-liganded and unliganded forms of CD3ε from a single species, which revealed that antibody binding does not induce any substantial rearrangements within CD3ε. Saturation mutagenesis of surface-exposed CD3ε residues, coupled with assays of antibody-induced signaling by the mutated complexes, suggests a new configuration for the complex within which CD3ε is highly exposed and reveals that no large new CD3ε interfaces are required to form during antibody-induced signaling. The TCR complex therefore appears to be a structure that is capable of initiating intracellular signaling in T cells without substantial structural rearrangements within or between the component subunits. Our findings raise the possibility that signaling by native ligands might also be initiated in the absence of large structural rearrangements in the receptor.
Assuntos
Complexo CD3 , Receptores de Antígenos de Linfócitos T , Transdução de Sinais/imunologia , Animais , Anticorpos Monoclonais/imunologia , Complexo CD3/química , Complexo CD3/genética , Complexo CD3/imunologia , Cristalografia por Raios X , Dimerização , Epitopos de Linfócito T/imunologia , Humanos , Fragmentos Fab das Imunoglobulinas/imunologia , Células Jurkat , Camundongos , Mutagênese Sítio-Dirigida , Conformação Proteica , Estrutura Terciária de Proteína , Receptores de Antígenos de Linfócitos T/química , Receptores de Antígenos de Linfócitos T/imunologia , Receptores de Antígenos de Linfócitos T/metabolismo , Relação Estrutura-AtividadeRESUMO
The inhibitory T-cell surface-expressed receptor, cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), which belongs to the class of cell surface proteins phosphorylated by extrinsic tyrosine kinases that also includes antigen receptors, binds the related ligands, B7-1 and B7-2, expressed on antigen-presenting cells. Conformational changes are commonly invoked to explain ligand-induced "triggering" of this class of receptors. Crystal structures of ligand-bound CTLA-4 have been reported, but not the apo form, precluding analysis of the structural changes accompanying ligand binding. The 1.8-Å resolution structure of an apo human CTLA-4 homodimer emphasizes the shared evolutionary history of the CTLA-4/CD28 subgroup of the immunoglobulin superfamily and the antigen receptors. The ligand-bound and unbound forms of both CTLA-4 and B7-1 are remarkably similar, in marked contrast to B7-2, whose binding to CTLA-4 has elements of induced fit. Isothermal titration calorimetry reveals that ligand binding by CTLA-4 is enthalpically driven and accompanied by unfavorable entropic changes. The similarity of the thermodynamic parameters determined for the interactions of CTLA-4 with B7-1 and B7-2 suggests that the binding is not highly specific, but the conformational changes observed for B7-2 binding suggest some level of selectivity. The new structure establishes that rigid-body ligand interactions are capable of triggering CTLA-4 phosphorylation by extrinsic kinase(s).
Assuntos
Antígenos CD/química , Antígeno B7-1/química , Antígeno B7-2/química , Receptores de Antígenos de Linfócitos T/química , Animais , Antígenos CD/genética , Antígenos CD/imunologia , Antígeno B7-1/genética , Antígeno B7-1/imunologia , Antígeno B7-2/genética , Antígeno B7-2/imunologia , Sítios de Ligação , Células CHO , Antígeno CTLA-4 , Cricetinae , Cricetulus , Cristalografia por Raios X , Humanos , Estrutura Terciária de Proteína , Receptores de Antígenos de Linfócitos T/genética , Receptores de Antígenos de Linfócitos T/imunologia , TermodinâmicaRESUMO
Mutations within MHC class I-restricted epitopes have been studied in relation to T cell-mediated immune escape, but their impact on NK cells via interaction with killer Ig-like receptors (KIRs) during early HIV infection is poorly understood. In two patients acutely infected with HIV-1, we observed the appearance of a mutation within the B*57-restricted TW10 epitope (G9E) that did not facilitate strong escape from T cell recognition. The NK cell receptor KIR3DL1, carried by these patients, is known to recognize HLA-B*5703 and is associated with good control of HIV-1. Therefore, we tested whether the G9E mutation influenced the binding of HLA-B*5703 to soluble KIR3DL1 protein by surface plasmon resonance, and while the wild-type sequence and a second (T3N) variant were recognized, the G9E variant abrogated KIR3DL1 binding. We extended the study to determine the peptide sensitivity of KIR3DL1 interaction with epitopes carrying mutations near the C termini of TW10 and a second HLA-B*57-restricted epitope, IW9. Several amino acid changes interfered with KIR3DL1 binding, the most extreme of which included the G9E mutation commonly selected by HLA-B*57. Our results imply that during HIV-1 infection, some early-emerging variants could affect KIR-HLA interaction, with possible implications for immune recognition.
Assuntos
Epitopos de Linfócito T/imunologia , Infecções por HIV/imunologia , Infecções por HIV/virologia , HIV-1/imunologia , Mutação de Sentido Incorreto , Receptores KIR3DL1/metabolismo , Substituição de Aminoácidos/genética , Epitopos de Linfócito T/genética , Epitopos de Linfócito T/metabolismo , HIV-1/genética , HIV-1/metabolismo , Antígenos HLA-B , Humanos , Evasão da Resposta Imune , Ligação Proteica , Ressonância de Plasmônio de SuperfícieRESUMO
Individuals with Down syndrome (DS) have more than 100-fold increased risk of acute megakaryoblastic leukemia (AMKL), but its pathogenesis is poorly understood. In this issue of the JCI, Arkoun et al. engineered stepwise DS-AMKL-associated mutations in GATA1, MPL, and SMC3 in human induced pluripotent stem cell (iPSC) clones from individuals with DS to dissect how each mutation affects gene expression control and megakaryocytic differentiation. The authors showed that the mutations cooperatively promote progression from transient myeloproliferative disorder to DS-AMKL. This study highlights the importance of mutation order and context in the perturbations of transcriptional and differentiation pathways involved in the evolution of hematologic malignancies, which will be critical for the development of preventative and therapeutic interventions.
Assuntos
Síndrome de Down , Células-Tronco Pluripotentes Induzidas , Leucemia Megacarioblástica Aguda , Leucemia , Criança , Síndrome de Down/complicações , Síndrome de Down/genética , Fator de Transcrição GATA1/genética , Humanos , Leucemia Megacarioblástica Aguda/genética , MutaçãoRESUMO
Glycoproteins present problems for structural analysis since they often have to be glycosylated in order to fold correctly and because their chemical and conformational heterogeneity generally inhibits crystallization. It is shown that the α-mannosidase I inhibitor kifunensine, which has previously been used for the purpose of glycoprotein crystallization in short-term (3-5â d) cultures, is apparently stable enough to be used to produce highly endoglycosidase H-sensitive glycoprotein in long-term (3-4â week) cultures of stably transfected Chinese hamster ovary (CHO) cells. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry-based analysis of the extracellular region of the cytotoxic T-lymphocyte antigen 4 (CTLA-4; CD152) homodimer expressed in long-term CHO cell cultures in the presence of kifunensine revealed that the inhibitor restricted CTLA-4 glycan processing to Man9GlcNAc2 and Man5GlcNAc2 structures. Complex-type glycans were undetectable, suggesting that the inhibitor was active for the entire duration of the cultures. Endoglycosidase treatment of the homodimer yielded protein that readily formed orthorhombic crystals with unit-cell parameters a=43.9, b=51.5, c=102.9â Å and space group P2(1)2(1)2(1) that diffracted to Bragg spacings of 1.8â Å. The results indicate that kifunensine will be effective in most, if not all, transient and long-term mammalian cell-based expression systems.
Assuntos
Alcaloides/química , Antígenos CD/química , Apoproteínas/química , Multimerização Proteica , Alcaloides/metabolismo , Animais , Antígenos CD/metabolismo , Apoproteínas/metabolismo , Células CHO , Antígeno CTLA-4 , Cricetinae , Cricetulus , Cristalização , Humanos , Polissacarídeos , Ligação Proteica , alfa-Manosidase/antagonistas & inibidoresRESUMO
BACKGROUND: To shed light on the earliest events in oncogenesis, there is growing interest in understanding the mutational landscapes of normal tissues across ages. In the last decade, next-generation sequencing of human tissues has revealed a surprising abundance of cells with what would be considered oncogenic mutations. AIMS: We performed meta-analysis on previously published sequencing data on normal tissues to categorize mutations based on their presence in cancer and showcase the quantity of cells with cancer-associated mutations in cancer-free individuals. METHODS AND RESULTS: We analyzed sequencing data from these studies of normal tissues to determine the prevalence of cells with mutations in three different categories across multiple age groups: 1) mutations in genes designated as drivers, 2) mutations that are in the Cancer Gene Census (CGC), and 3) mutations in the CGC that are considered pathogenic. As we age, the percentage of cells in all three levels increase significantly, reaching over 50% of cells having oncogenic mutations for multiple tissues in the older age groups. The clear enrichment for these mutations, particularly at older ages, likely indicates strong selection for the resulting phenotypes. Combined with an estimation of the number of cells in tissues, we calculate that most older, cancer-free individuals possess at least a 100 billion cells that harbor at least one oncogenic mutation, presumably emanating from a fitness advantage conferred by these mutations that promotes clonal expansion. CONCLUSIONS: These studies of normal tissues have highlighted the specific drivers of clonal expansion and how frequently they appear in us. Their high prevalence throughout cancer-free individuals necessitates reconsideration of the oncogenicity of these mutations, which could shape methods of detection, prevention and treatment of cancer, as well as of the potential impact of these mutations on tissue function and our health.
RESUMO
A full understanding of leukocyte responses to external stimuli requires knowledge of the full complement of proteins found on their surfaces. Systematic examination of the mammalian cell surfaces at the protein level is hampered by technical difficulties associated with proteomic analysis of so many membrane proteins and the large amounts of starting material required. The use of transcriptomic analyses avoids challenges associated with protein stability and separation and enables the inclusion of an amplification step; thus allowing the use of cell numbers applicable to the study of sub populations of, for example, primary lymphocytes. Here we present a transcriptomic methodology based on Serial Analysis of Gene Expression (SAGE) to recover an essentially complete and quantitative profile of mRNA species in a particular cell. We discuss how, using bioinformatic tools accessible to standard desktop computers, plasma membrane proteins can be identified in silico, from this list. While we describe the use of this approach to characterise the cell surface protein complement of a resting CD8(+) T-cell clone, it is theoretically applicable to any cell surface, where a suitable pure population of cells is available.
Assuntos
Biologia Computacional/métodos , Perfilação da Expressão Gênica/métodos , Proteínas de Membrana/análise , Proteínas de Membrana/genética , Antígenos CD8/análise , Antígenos CD8/genética , Linhagem Celular , Membrana Celular/química , Membrana Celular/genética , Bases de Dados Genéticas , Expressão Gênica , Humanos , RNA Mensageiro/genética , Software , Linfócitos T/química , Linfócitos T/citologiaRESUMO
Glycoproteins present special problems for structural genomic analysis because they often require glycosylation in order to fold correctly, whereas their chemical and conformational heterogeneity generally inhibits crystallization. We show that the "glycosylation problem" can be solved by expressing glycoproteins transiently in mammalian cells in the presence of the N-glycosylation processing inhibitors, kifunensine or swainsonine. This allows the correct folding of the glycoproteins, but leaves them sensitive to enzymes, such as endoglycosidase H, that reduce the N-glycans to single residues, enhancing crystallization. Since the scalability of transient mammalian expression is now comparable to that of bacterial systems, this approach should relieve one of the major bottlenecks in structural genomic analysis.
Assuntos
Genômica , Glicoproteínas/química , Glicoproteínas/metabolismo , Alcaloides/química , Alcaloides/genética , Alcaloides/metabolismo , Linhagem Celular , Clonagem Molecular , Inibidores Enzimáticos , Genômica/métodos , Glicoproteínas/antagonistas & inibidores , Glicoproteínas/genética , Glicosilação/efeitos dos fármacos , Humanos , Swainsonina/química , Swainsonina/metabolismoRESUMO
BACKGROUND: Deep transcriptome analysis will underpin a large fraction of post-genomic biology. 'Closed' technologies, such as microarray analysis, only detect the set of transcripts chosen for analysis, whereas 'open' e.g. tag-based technologies are capable of identifying all possible transcripts, including those that were previously uncharacterized. Although new technologies are now emerging, at present the major resources for open-type analysis are the many publicly available SAGE (serial analysis of gene expression) and MPSS (massively parallel signature sequencing) libraries. These technologies have never been compared for their utility in the context of deep transcriptome mining. RESULTS: We used a single LongSAGE library of 503,431 tags and a "classic" MPSS library of 1,744,173 tags, both prepared from the same T cell-derived RNA sample, to compare the ability of each method to probe, at considerable depth, a human cellular transcriptome. We show that even though LongSAGE is more error-prone than MPSS, our LongSAGE library nevertheless generated 6.3-fold more genome-matching (and therefore likely error-free) tags than the MPSS library. An analysis of a set of 8,132 known genes detectable by both methods, and for which there is no ambiguity about tag matching, shows that MPSS detects only half (54%) the number of transcripts identified by SAGE (3,617 versus 1,955). Analysis of two additional MPSS libraries shows that each library samples a different subset of transcripts, and that in combination the three MPSS libraries (4,274,992 tags in total) still only detect 73% of the genes identified in our test set using SAGE. The fraction of transcripts detected by MPSS is likely to be even lower for uncharacterized transcripts, which tend to be more weakly expressed. The source of the loss of complexity in MPSS libraries compared to SAGE is unclear, but its effects become more severe with each sequencing cycle (i.e. as MPSS tag length increases). CONCLUSION: We show that MPSS libraries are significantly less complex than much smaller SAGE libraries, revealing a serious bias in the generation of MPSS data unlikely to have been circumvented by later technological improvements. Our results emphasize the need for the rigorous testing of new expression profiling technologies.
Assuntos
Perfilação da Expressão Gênica , Mapeamento Cromossômico , Biologia Computacional , Bases de Dados Genéticas , Etiquetas de Sequências Expressas , Genoma Humano , HumanosRESUMO
Improved activation of adsorbed O2 by co-adsorbed H2O on the Pd-Au(111) surface has been observed. When co-adsorbed with H2O, O2 admolecules on the Pd-Au surface are more strongly bound via their interactions with H2O. This interaction leads to large enhancements in the dissociation of O2 as determined via the generation of CO2 upon exposure to CO.
RESUMO
There has been debate on whether Ni(OH)2 is truly catalytically active for the photo/electrocatalytic oxygen evolution reaction. In this report, we synthesized a Ni(OH)2 cocatalyst on a hematite photoanode and showed that, as has been proposed in other studies, the current density varies as a function of scan rate, which arises due to a photoinduced capacitive charging effect. We discovered that this photoinduced charging of Ni2+/3+ can be overcome by mixing cerium nitrate into the Ni precursor solution. Under illumination, the NiCeOx cocatalyst on a hematite photoanode exhibited an approximately 200 mV cathodic shift in onset potential and a â¼53% enhancement in photocurrent at 1.23 V vs RHE. Material characterization by electrochemical impedance spectroscopy revealed that the Ni species create a p-n junction across the charge space region, which facilitates collection of the photogenerated holes by the cocatalyst layer, and core level X-ray photoelectron spectroscopy showed that Ce incorporated into the Ni-based cocatalyst layer may possibly induce the oxidation of the Ni species. In addition, we observed a reduction in binding energies of Ni after photoelectrochemical water splitting reactions, which suggests that the lattice oxygen of the NiCeOx is consumed in the catalytic cycle, forming oxygen vacancies. The NiCeOx cocatalyst, however, was incapable of passivating the surface recombination centers of the hematite photoanode, as indicated by the unaltered flat-band potential determined with Mott-Schottky analysis.
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We present the crystal structure of an immunoglobulin light-chain-like domain, CTLA-4, as a strand-swapped dimer displaying cis-trans proline isomerisation and native-like hydrogen bonding. We also show that CTLA-4 can form amyloid-like fibres and amorphous deposits explainable by the same strand swapping. Our results suggest a molecular basis for the pathological aggregation of immunoglobulin domains and why amyloid-like fibres are more often composed of homologous rather than heterologous subunits.