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1.
Sci Rep ; 14(1): 1901, 2024 01 22.
Artigo em Inglês | MEDLINE | ID: mdl-38253624

RESUMO

To motivate contributions to public goods, should policy makers employ financial incentives like taxes, fines, subsidies, and rewards? While these are widely considered as the classic policy approach, a substantial academic literature suggests the impact of financial incentives is not always positive; they can sometimes fail or even backfire. To test whether policy makers are overly bullish about financial incentives, we asked county heads, mayors, and municipal government representatives of medium-to-large towns in Germany to predict the effects of a financial incentive on COVID-19 vaccination, and tested the exact same incentive in a field experiment involving all 41,548 inhabitants (clustered in 10,032 addresses) of the German town of Ravensburg. Whereas policy makers overwhelmingly predict that the financial incentive will increase vaccination-by 15.3 percentage points on average-the same financial incentive yielded a precisely estimated null effect on vaccination. We discuss when financial incentives are most likely to fail, and conclude that it is critical to educate policy makers on the potential pitfalls of employing financial incentives to promote contributions to public goods.


Assuntos
Pessoal Administrativo , Vacinas contra COVID-19 , Humanos , Alemanha , Governo Local , Políticas
2.
J Am Chem Soc ; 145(51): 27958-27974, 2023 12 27.
Artigo em Inglês | MEDLINE | ID: mdl-38104324

RESUMO

Lassa virus is a negative-strand RNA virus with only four structural proteins that causes periodic outbreaks in West Africa. The nucleoprotein (NP) encapsidates the viral genome, forming ribonucleoprotein complexes (RNPs) together with the viral RNA and the L protein. RNPs must be continuously restructured during viral genome replication and transcription. The Z protein is important for membrane recruitment of RNPs, viral particle assembly, and budding and has also been shown to interact with the L protein. However, the interaction of NP, viral RNA, and Z is poorly understood. Here, we characterize the interactions between Lassa virus NP, Z, and RNA using structural mass spectrometry. We identify the presence of RNA as the driver for the disassembly of ring-like NP trimers, a storage form, into monomers to subsequently form higher order RNA-bound NP assemblies. We locate the interaction site of Z and NP and demonstrate that while NP binds Z independently of the presence of RNA, this interaction is pH-dependent. These data improve our understanding of RNP assembly, recruitment, and release in Lassa virus.


Assuntos
Vírus Lassa , Ribonucleoproteínas , Vírus Lassa/genética , Vírus Lassa/metabolismo , Ribonucleoproteínas/química , Nucleoproteínas , Montagem de Vírus , RNA Viral/genética , RNA Viral/metabolismo
3.
Sci Rep ; 13(1): 22820, 2023 12 20.
Artigo em Inglês | MEDLINE | ID: mdl-38129678

RESUMO

Bunyaviruses constitute a large and diverse group of viruses encompassing many emerging pathogens, such as Rift Valley fever virus (family Phenuiviridae), with public and veterinary health relevance but with very limited medical countermeasures are available. For the development of antiviral strategies, the identification and validation of virus-specific targets would be of high value. The cap-snatching mechanism is an essential process in the life cycle of bunyaviruses to produce capped mRNAs, which are then recognized and translated into viral proteins by the host cell translation machinery. Cap-snatching involves cap-binding as well as endonuclease functions and both activities have been demonstrated to be druggable in related influenza viruses. Here, we explore the suitability of the phenuivirus cap-binding function as a target in medium- and high-throughput drug discovery approaches. We developed a range of in vitro assays aiming to detect the interaction between the cap-binding domain (CBD) and the analogue of its natural cap-ligand m7GTP. However, constricted by its shallow binding pocket and low affinity for m7GTP, we conclude that the CBD has limited small molecule targeting potential using classical in vitro drug discovery approaches.


Assuntos
Orthobunyavirus , Orthomyxoviridae , Vírus de RNA , Animais , Capuzes de RNA/metabolismo , Ensaios de Triagem em Larga Escala , RNA Mensageiro/metabolismo , Vírus de RNA/metabolismo , Orthomyxoviridae/metabolismo
4.
PLoS Pathog ; 19(8): e1011533, 2023 08.
Artigo em Inglês | MEDLINE | ID: mdl-37549153

RESUMO

The Bunyavirales order is a large and diverse group of segmented negative-strand RNA viruses. Several virus families within this order contain important human pathogens, including Sin Nombre virus (SNV) of the Hantaviridae. Despite the high epidemic potential of bunyaviruses, specific medical countermeasures such as vaccines or antivirals are missing. The multifunctional ~250 kDa L protein of hantaviruses, amongst other functional domains, harbors the RNA-dependent RNA polymerase (RdRp) and an endonuclease and catalyzes transcription as well as replication of the viral RNA genome, making it a promising therapeutic target. The development of inhibitors targeting these key processes requires a profound understanding of the catalytic mechanisms. Here, we established expression and purification protocols of the full-length SNV L protein bearing the endonuclease mutation K124A. We applied different biochemical in vitro assays to provide an extensive characterization of the different enzymatic functions as well as the capacity of the hantavirus L protein to interact with the viral RNA. By using single-particle cryo-EM, we obtained a 3D model including the L protein core region containing the RdRp, in complex with the 5' promoter RNA. This first high-resolution model of a New World hantavirus L protein shows striking similarity to related bunyavirus L proteins. The interaction of the L protein with the 5' RNA observed in the structural model confirms our hypothesis of protein-RNA binding based on our biochemical data. Taken together, this study provides an excellent basis for future structural and functional studies on the hantavirus L protein and for the development of antiviral compounds.


Assuntos
Bunyaviridae , Orthohantavírus , Vírus de RNA , Vírus Sin Nombre , Humanos , Vírus Sin Nombre/genética , Vírus Sin Nombre/metabolismo , Orthohantavírus/genética , RNA Polimerase Dependente de RNA/genética , Bunyaviridae/metabolismo , RNA Viral/genética , Vírus de RNA/genética , Endonucleases/genética , Endonucleases/metabolismo
5.
Front Med (Lausanne) ; 10: 1098547, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-36923010

RESUMO

An impressive effect of the infection with SARS-Co-19 is the impairment of oxygen uptake due to lung injury. The reduced oxygen diffusion may potentially be counteracted by an increase in oxygen affinity of hemoglobin. However, hypoxia and anemia associated with COVID-19 usually decrease oxygen affinity due to a rise in [2,3-bisphosphoglycerate]. As such, COVID-19 related changes in the oxygen dissociation curve may be critical for oxygen uptake and supply, but are hard to predict. A Pubmed search lists 14 publications on oxygen affinity in COVID-19. While some investigations show no changes, three large studies found an increased affinity that was related to a good prognosis. Exact causes remain unknown. The cause of the associated anemia in COVID-19 is under discussion. Erythrocytes with structural alterations of membrane and cytoskeleton have been observed, and virus binding to Band 3 and also to ACE2 receptors in erythroblasts has been proposed. COVID-19 presentation is moderate in many subjects suffering from sickle cell disease. A possible explanation is that COVID-19 counteracts the unfavorable large right shift of the oxygen dissociation curve in these patients. Under discussion for therapy are mainly affinity-increasing drugs.

6.
Nucleic Acids Res ; 51(3): 1424-1442, 2023 02 22.
Artigo em Inglês | MEDLINE | ID: mdl-36651274

RESUMO

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a phenuivirus that has rapidly become endemic in several East Asian countries. The large (L) protein of SFTSV, which includes the RNA-dependent RNA polymerase (RdRp), is responsible for catalysing viral genome replication and transcription. Here, we present 5 cryo-electron microscopy (cryo-EM) structures of the L protein in several states of the genome replication process, from pre-initiation to late-stage elongation, at a resolution of up to 2.6 Å. We identify how the L protein binds the 5' viral RNA in a hook-like conformation and show how the distal 5' and 3' RNA ends form a duplex positioning the 3' RNA terminus in the RdRp active site ready for initiation. We also observe the L protein stalled in the early and late stages of elongation with the RdRp core accommodating a 10-bp product-template duplex. This duplex ultimately splits with the template binding to a designated 3' secondary binding site. The structural data and observations are complemented by in vitro biochemical and cell-based mini-replicon assays. Altogether, our data provide novel key insights into the mechanism of viral genome replication by the SFTSV L protein and will aid drug development against segmented negative-strand RNA viruses.


Assuntos
Phlebovirus , Febre Grave com Síndrome de Trombocitopenia , Humanos , Febre Grave com Síndrome de Trombocitopenia/genética , Microscopia Crioeletrônica , RNA Viral/genética , RNA Polimerase Dependente de RNA/metabolismo , Phlebovirus/genética , Replicação Viral , Genoma Viral
7.
Public Adm Rev ; 2023 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-36718222

RESUMO

During a global pandemic, individual views of government can be linked to citizens' trust and cooperation with government and their propensity to resist state policies or to take action that influences the course of a pandemic. This article explores citizens' assessments of government responses to COVID-19 as a function of policy substance (restrictions on civil liberties), information about performance, and socioeconomic inequity in outcomes. We conducted a survey experiment and analyzed data on over 7000 respondents from eight democratic countries. We find that across countries, citizens are less favorable toward COVID-19 policies that are more restrictive of civil liberties. Additionally, citizens' views of government performance are significantly influenced by objective performance information from reputable sources and information on the disproportionate impacts of COVID-19 on low-income groups. This study reinforces the importance of policy design and outcomes and the consideration of multiple public values in the implementation of public policies.

8.
Nat Commun ; 12(1): 7018, 2021 12 02.
Artigo em Inglês | MEDLINE | ID: mdl-34857749

RESUMO

Lassa virus is endemic in West Africa and can cause severe hemorrhagic fever. The viral L protein transcribes and replicates the RNA genome via its RNA-dependent RNA polymerase activity. Here, we present nine cryo-EM structures of the L protein in the apo-, promoter-bound pre-initiation and active RNA synthesis states. We characterize distinct binding pockets for the conserved 3' and 5' promoter RNAs and show how full-promoter binding induces a distinct pre-initiation conformation. In the apo- and early elongation states, the endonuclease is inhibited by two distinct L protein peptides, whereas in the pre-initiation state it is uninhibited. In the early elongation state, a template-product duplex is bound in the active site cavity together with an incoming non-hydrolysable nucleotide and the full C-terminal region of the L protein, including the putative cap-binding domain, is well-ordered. These data advance our mechanistic understanding of how this flexible and multifunctional molecular machine is activated.


Assuntos
Vírus Lassa/genética , RNA Viral/química , RNA Polimerase Dependente de RNA/química , Transcrição Gênica , Proteínas Virais/química , Motivos de Aminoácidos , Domínio Catalítico , Clonagem Molecular , Escherichia coli/genética , Escherichia coli/metabolismo , Expressão Gênica , Vetores Genéticos/química , Vetores Genéticos/metabolismo , Vírus Lassa/química , Vírus Lassa/enzimologia , Modelos Moleculares , Regiões Promotoras Genéticas , Ligação Proteica , Conformação Proteica em alfa-Hélice , Conformação Proteica em Folha beta , Domínios e Motivos de Interação entre Proteínas , RNA Viral/biossíntese , RNA Viral/genética , RNA Polimerase Dependente de RNA/genética , RNA Polimerase Dependente de RNA/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Especificidade por Substrato , Proteínas Virais/genética , Proteínas Virais/metabolismo
11.
Crit Care Explor ; 3(2): e0345, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33634265

RESUMO

OBJECTIVES: Changes in right ventricular size and function are frequently observed in patients with severe acute respiratory distress syndrome. The majority of patients who receive venovenous extracorporeal membrane oxygenation undergo chest CT and transthoracic echocardiography. The aims of this study were to compare the use of CT and transthoracic echocardiography to evaluate the right ventricular function and to determine the prevalence of acute cor pulmonale in this patient population. DESIGN: Observational, retrospective, single-center, cohort study. SETTING: Severe respiratory failure and extracorporeal membrane oxygenation center. PATIENTS: About 107 patients with severe acute respiratory distress syndrome managed with venovenous extracorporeal membrane oxygenation. INTERVENTIONS: Chest CT to evaluate right ventricular size and transthoracic echocardiography to evaluate right ventricular size and function. MEASUREMENTS AND MAIN RESULTS: All 107 patients had a qualitative assessment of right ventricular size and function on transthoracic echocardiography. Quantitative measurements were available in 54 patients (50%) who underwent transthoracic echocardiography and in 107 of patients (100%) who received CT. Right ventricular dilatation was defined as a right ventricle end-diastolic diameter greater than left ventricular end-diastolic diameter upon visual assessment or an right ventricle end-diastolic diameter/left ventricular end-diastolic diameter and/or right ventricle cavity area/left ventricular cavity area of greater than 0.9. Right ventricle systolic function was visually estimated as being normal or impaired (visual right ventricular systolic impairment). The right ventricle was found to be dilated in 38/107 patients (36%) and in 58/107 patients (54%), using transthoracic echocardiography or CT right ventricle end-diastolic diameter/left ventricular end-diastolic diameter, respectively. When the CT right ventricle cavity/left ventricular cavity area criterion was used, the right ventricle was dilated in 19/107 patients (18%). About 33/107 patients (31%) exhibited visual right ventricular systolic impairment. Transthoracic echocardiography right ventricle end-diastolic diameter/left ventricular end-diastolic diameter showed good agreement with CT right ventricle cavity/left ventricular cavity area (R 2 = 0.57; p < 0.01). A CT right ventricle cavity/left ventricular cavity area greater than 0.9 provided the optimal cutoff for acute cor pulmonale on transthoracic echocardiography with an AUC of 0.78. Acute cor pulmonale was defined by the presence of a right ventricle "D-shape" and quantitative right ventricle dilatation on transthoracic echocardiography or a right ventricle cavity/left ventricular cavity area greater than 0.9 on CT. A diagnosis of acute cor pulmonale was made in 9/54 (14% patients) on transthoracic echocardiography and in 19/107 (18%) on CT. CONCLUSIONS: Changes in right ventricular size and function are common in patients with severe acute respiratory distress syndrome requiring venovenous extracorporeal membrane oxygenation with up to 18% showing imaging evidence of acute cor pulmonale. A CT right ventricular cavity /left ventricular cavity area greater than 0.9 is indicative of impaired right ventricular systolic function.

12.
Respir Med Case Rep ; 32: 101351, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33537201

RESUMO

A broncho-cutaneous fistula (BCF) is a communicating tract between the bronchus and the cutaneous surface of the thoracic wall and can be the primary presenting sign of several disease processes. It has been associated with positive pressure ventilation (PPV), post pneumonectomy, thoracostomy tubes, perforating chest trauma, neoplasia and chronic empyema. We report a case of a 45-year-old immunocompetent man presenting with severe hypercapnic respiratory failure secondary to a BCF as a result of tuberculosis (TB)-related empyema necessitans. Veno-venous extracorporeal membrane oxygenation (VV ECMO) was employed during spontaneous breathing to mitigate the risks of PPV, to facilitate diagnostics and enable targeted treatment. Awake VV ECMO is an effective supportive therapy for complex, destructive lung pathologies with a known reversible aetiology in which PPV would be potentially detrimental.

14.
Br J Haematol ; 191(3): 390-393, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-33037620

RESUMO

Critically ill patients with coronavirus disease 2019 (COVID-19) present with hypoxaemia and are mechanically ventilated to support gas exchange. We performed a retrospective, observational study of blood gas analyses (n = 3518) obtained from patients with COVID-19 to investigate changes in haemoglobin oxygen (Hb-O2 ) affinity. Calculated oxygen tension at half-saturation (p50 ) was on average (±SD) 3·3 (3·13) mmHg lower than the normal p50 value (23·4 vs. 26·7 mmHg; P < 0·0001). Compared to an unmatched historic control of patients with other causes of severe respiratory failure, patients with COVID-19 had a significantly higher Hb-O2 affinity (mean [SD] p50 23·4 [3·13] vs. 24·6 [5.4] mmHg; P < 0·0001). We hypothesise that, due to the long disease process, acclimatisation to hypoxaemia could play a role.


Assuntos
Betacoronavirus , Infecções por Coronavirus/sangue , Oxiemoglobinas/metabolismo , Pneumonia Viral/sangue , Adulto , Idoso , COVID-19 , Dióxido de Carbono/sangue , Dispneia/sangue , Dispneia/etiologia , Feminino , Humanos , Concentração de Íons de Hidrogênio , Hipóxia/sangue , Hipóxia/etiologia , Masculino , Pessoa de Meia-Idade , Modelos Cardiovasculares , Oxigênio/sangue , Pandemias , Pressão Parcial , Estudos Retrospectivos , SARS-CoV-2
15.
Nucleic Acids Res ; 48(10): 5749-5765, 2020 06 04.
Artigo em Inglês | MEDLINE | ID: mdl-32313945

RESUMO

The Bunyavirales order contains several emerging viruses with high epidemic potential, including Severe fever with thrombocytopenia syndrome virus (SFTSV). The lack of medical countermeasures, such as vaccines and antivirals, is a limiting factor for the containment of any virus outbreak. To develop such antivirals a profound understanding of the viral replication process is essential. The L protein of bunyaviruses is a multi-functional and multi-domain protein performing both virus transcription and genome replication and, therefore, is an ideal drug target. We established expression and purification procedures for the full-length L protein of SFTSV. By combining single-particle electron cryo-microscopy and X-ray crystallography, we obtained 3D models covering ∼70% of the SFTSV L protein in the apo-conformation including the polymerase core region, the endonuclease and the cap-binding domain. We compared this first L structure of the Phenuiviridae family to the structures of La Crosse peribunyavirus L protein and influenza orthomyxovirus polymerase. Together with a comprehensive biochemical characterization of the distinct functions of SFTSV L protein, this work provides a solid framework for future structural and functional studies of L protein-RNA interactions and the development of antiviral strategies against this group of emerging human pathogens.


Assuntos
RNA Polimerases Dirigidas por DNA/química , Phlebovirus/enzimologia , Proteínas Virais/química , Microscopia Crioeletrônica , RNA Polimerases Dirigidas por DNA/metabolismo , Endorribonucleases/metabolismo , Modelos Moleculares , Phlebovirus/genética , Regiões Promotoras Genéticas , Domínios Proteicos , Vírus de RNA/enzimologia , Proteínas Virais/metabolismo , Replicação Viral
16.
J Biol Chem ; 294(20): 8088-8100, 2019 05 17.
Artigo em Inglês | MEDLINE | ID: mdl-30926610

RESUMO

The L protein of arena- and bunyaviruses is structurally and functionally related to the orthomyxovirus polymerase complex. It plays a central role in the viral life cycle, as it replicates the virus genome and generates viral mRNA via a cap-snatching mechanism. Here, we aimed to biochemically characterize the L protein of Lassa virus, a human-pathogenic arenavirus endemic in West Africa. Full-length 250-kDa L protein was expressed using a baculovirus expression system. A low-resolution structure calculated from small-angle X-ray scattering data revealed a conformation similar to that in the crystal structure of the orthomyxovirus polymerase complex. Although the L protein did not exhibit cap-snatching endonuclease activity, it synthesized RNA in vitro RNA polymerization required manganese rather than magnesium ions, was independent of nucleotide primers, and was inhibited by viral Z protein. Maximum activity was mediated by double-stranded promoter sequences with a minimum length of 17 nucleotides, containing a nontemplated 5'-G overhang, as in the natural genome context, as well as the naturally occurring base mismatches between the complementary promoter strands. Experiments with various short primers revealed the presence of two replication initiation sites at the template strand and evidence for primer translocation as proposed by the prime-and-realign hypothesis. Overall, our findings provide the foundation for a detailed understanding of the mechanistic differences and communalities in the polymerase proteins of segmented negative-strand RNA viruses and for the search for antiviral compounds targeting the RNA polymerase of Lassa virus.


Assuntos
Vírus Lassa , Regiões Promotoras Genéticas , RNA Viral , DNA Polimerase Dirigida por RNA , Proteínas Virais , Cristalografia por Raios X , Humanos , Vírus Lassa/enzimologia , Vírus Lassa/genética , RNA Viral/biossíntese , RNA Viral/química , RNA Viral/genética , DNA Polimerase Dirigida por RNA/química , DNA Polimerase Dirigida por RNA/genética , DNA Polimerase Dirigida por RNA/metabolismo , Proteínas Virais/química , Proteínas Virais/genética , Proteínas Virais/metabolismo
17.
Brain Cogn ; 131: 10-21, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-30502227

RESUMO

BACKGROUND: Functional connectivity (fcMRI) analyses of resting state functional magnetic resonance imaging (fMRI) data revealed substantial differences between states of consciousness. The underlying cause-effect linkage, however, remains unknown to the present day. The aim of this study was to examine the relationship between fcMRI measures and Disorders of Consciousness (DOC) in resting state and under adequate stimulation. METHODS AND FINDINGS: fMRI data from thirteen patients with unresponsive wakefulness syndrome, eight patients in minimally conscious state, and eleven healthy controls were acquired in rest and during the application of nociceptive and emotional acoustic stimuli. We compared spatial characteristics and anatomical topography of seed-based fcMRI networks on group and individual levels. The anatomical topography of fcMRI networks of patients was altered in all three conditions as compared with healthy controls. Spread and distribution of individual fcMRI networks, however, differed significantly between patients and healthy controls in stimulation conditions only. The exploration of individual metric values identified two patients whose spatial metrics did not deviate from metric distributions of healthy controls in a statistically meaningful manner. CONCLUSIONS: These findings suggest that the disturbance of consciousness in DOC is related to deficits in global topographical network organization rather than a principal inability to establish long-distance connections. In addition, the results question the claim that task-free measurements are particularly valuable as a tool for individual diagnostics in severe neurological disorders. Further studies comparing connectivity indices with outcome of DOC patients are needed to determine the clinical relevance of spatial metrics and stimulation paradigms for individual diagnosis, prognosis and treatment in DOC.


Assuntos
Encéfalo/diagnóstico por imagem , Transtornos da Consciência/diagnóstico por imagem , Estado de Consciência/fisiologia , Rede Nervosa/diagnóstico por imagem , Estimulação Acústica , Adolescente , Adulto , Idoso , Encéfalo/fisiopatologia , Transtornos da Consciência/fisiopatologia , Eletroencefalografia , Feminino , Humanos , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Rede Nervosa/fisiopatologia , Descanso , Adulto Jovem
18.
Perfusion ; 33(1_suppl): 57-64, 2018 05.
Artigo em Inglês | MEDLINE | ID: mdl-29788842

RESUMO

INTRODUCTION: The role of extracorporeal support for patients with septic shock remains unclear. METHODS: We conducted a retrospective analysis of our single-centre experience with veno-arterio-venous extracorporeal membrane oxygenation (VAV ECMO) in adult patients with severe respiratory failure and septic cardiomyopathy. Clinical data was extracted from electronic medical records including a dedicated ECMO referral and follow-up database. RESULTS: Twelve patients were commenced on VAV ECMO for septic cardiomyopathy for a median of four days (IQR 3.0 to 5.3) between 01/2014 and 12/2017. Five patients (41.7%) had a cardiac arrest prior to initiation of ECMO support. At baseline, median left ventricular ejection fraction was 16.25% (IQR 13.13 to 17.5) and median PaO2/FiO2 ratio was 9 kPa (IQR 6.5 to 12.0) [67.50 mmHg (IQR 48.75 to 90.00)]. The survival rate to hospital discharge for VAV ECMO was 75% in this cohort. None of the surviving patients died within the follow-up period (median six month). CONCLUSION: VAV ECMO is a feasible rescue strategy for a small proportion of patients with combined respiratory and cardiac failure secondary to septic shock with septic cardiomyopathy. We provide a detailed report of our experience with this technique. Further research is required comparing the different extracorporeal strategies directly to conventional resuscitation and against each other.


Assuntos
Cardiomiopatias/terapia , Oxigenação por Membrana Extracorpórea/métodos , Adulto , Cardiomiopatias/patologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Resultado do Tratamento , Adulto Jovem
19.
Phys Rev Lett ; 118(24): 240403, 2017 Jun 16.
Artigo em Inglês | MEDLINE | ID: mdl-28665652

RESUMO

Topological defects in Bloch bands, such as Dirac points in graphene, and their resulting Berry phases play an important role for the electronic dynamics in solid state crystals. Such defects can arise in systems with a two-atomic basis due to the momentum-dependent coupling of the two sublattice states, which gives rise to a pseudospin texture. The topological defects appear as vortices in the azimuthal phase of this pseudospin texture. Here, we demonstrate a complete measurement of the azimuthal phase in a hexagonal optical lattice employing a versatile method based on time-of-flight imaging after off-resonant lattice modulation. Furthermore, we map out the merging transition of the two Dirac points induced by beam imbalance. Our work paves the way to accessing geometric properties in optical lattices also with spin-orbit coupling and interactions.

20.
PLoS Pathog ; 13(5): e1006400, 2017 May.
Artigo em Inglês | MEDLINE | ID: mdl-28505175

RESUMO

Cap-snatching was first discovered in influenza virus. Structures of the involved domains of the influenza virus polymerase, namely the endonuclease in the PA subunit and the cap-binding domain in the PB2 subunit, have been solved. Cap-snatching endonucleases have also been demonstrated at the very N-terminus of the L proteins of mammarena-, orthobunya-, and hantaviruses. However, a cap-binding domain has not been identified in an arena- or bunyavirus L protein so far. We solved the structure of the 326 C-terminal residues of the L protein of California Academy of Sciences virus (CASV), a reptarenavirus, by X-ray crystallography. The individual domains of this 37-kDa fragment (L-Cterm) as well as the domain arrangement are structurally similar to the cap-binding and adjacent domains of influenza virus polymerase PB2 subunit, despite the absence of sequence homology, suggesting a common evolutionary origin. This enabled identification of a region in CASV L-Cterm with similarity to a cap-binding site; however, the typical sandwich of two aromatic residues was missing. Consistent with this, cap-binding to CASV L-Cterm could not be detected biochemically. In addition, we solved the crystal structure of the corresponding endonuclease in the N-terminus of CASV L protein. It shows a typical endonuclease fold with an active site configuration that is essentially identical to that of known mammarenavirus endonuclease structures. In conclusion, we provide evidence for a presumably functional cap-snatching endonuclease in the N-terminus and a degenerate cap-binding domain in the C-terminus of a reptarenavirus L protein. Implications of these findings for the cap-snatching mechanism in arenaviruses are discussed.


Assuntos
Infecções por Arenaviridae/virologia , Arenaviridae/enzimologia , Endonucleases/metabolismo , Modelos Moleculares , Arenaviridae/química , Arenaviridae/genética , Cristalografia por Raios X , Endonucleases/química , Endonucleases/genética , Conformação Proteica , Domínios Proteicos , Capuzes de RNA , Proteínas Virais/química , Proteínas Virais/genética , Proteínas Virais/metabolismo
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