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1.
Cell ; 186(19): 4059-4073.e27, 2023 09 14.
Artigo em Inglês | MEDLINE | ID: mdl-37611581

RESUMO

Antimicrobial resistance is a leading mortality factor worldwide. Here, we report the discovery of clovibactin, an antibiotic isolated from uncultured soil bacteria. Clovibactin efficiently kills drug-resistant Gram-positive bacterial pathogens without detectable resistance. Using biochemical assays, solid-state nuclear magnetic resonance, and atomic force microscopy, we dissect its mode of action. Clovibactin blocks cell wall synthesis by targeting pyrophosphate of multiple essential peptidoglycan precursors (C55PP, lipid II, and lipid IIIWTA). Clovibactin uses an unusual hydrophobic interface to tightly wrap around pyrophosphate but bypasses the variable structural elements of precursors, accounting for the lack of resistance. Selective and efficient target binding is achieved by the sequestration of precursors into supramolecular fibrils that only form on bacterial membranes that contain lipid-anchored pyrophosphate groups. This potent antibiotic holds the promise of enabling the design of improved therapeutics that kill bacterial pathogens without resistance development.


Assuntos
Antibacterianos , Bactérias , Microbiologia do Solo , Antibacterianos/isolamento & purificação , Antibacterianos/farmacologia , Bioensaio , Difosfatos
2.
Cell ; 173(5): 1244-1253.e10, 2018 05 17.
Artigo em Inglês | MEDLINE | ID: mdl-29681455

RESUMO

The RIPK1-RIPK3 necrosome is an amyloid signaling complex that initiates TNF-induced necroptosis, serving in human immune defense, cancer, and neurodegenerative diseases. RIPK1 and RIPK3 associate through their RIP homotypic interaction motifs with consensus sequences IQIG (RIPK1) and VQVG (RIPK3). Using solid-state nuclear magnetic resonance, we determined the high-resolution structure of the RIPK1-RIPK3 core. RIPK1 and RIPK3 alternately stack (RIPK1, RIPK3, RIPK1, RIPK3, etc.) to form heterotypic ß sheets. Two such ß sheets bind together along a compact hydrophobic interface featuring an unusual ladder of alternating Ser (from RIPK1) and Cys (from RIPK3). The crystal structure of a four-residue RIPK3 consensus sequence is consistent with the architecture determined by NMR. The RIPK1-RIPK3 core is the first detailed structure of a hetero-amyloid and provides a potential explanation for the specificity of hetero- over homo-amyloid formation and a structural basis for understanding the mechanisms of signal transduction.


Assuntos
Amiloide/química , Proteína Serina-Treonina Quinases de Interação com Receptores/química , Sequência de Aminoácidos , Cristalografia por Raios X , Humanos , Ressonância Magnética Nuclear Biomolecular , Domínios e Motivos de Interação entre Proteínas , Estrutura Secundária de Proteína , Proteína Serina-Treonina Quinases de Interação com Receptores/metabolismo , Alinhamento de Sequência
3.
Annu Rev Biochem ; 86: 69-95, 2017 06 20.
Artigo em Inglês | MEDLINE | ID: mdl-28125289

RESUMO

Dozens of proteins are known to convert to the aggregated amyloid state. These include fibrils associated with systemic and neurodegenerative diseases and cancer, functional amyloid fibrils in microorganisms and animals, and many denatured proteins. Amyloid fibrils can be much more stable than other protein assemblies. In contrast to globular proteins, a single protein sequence can aggregate into several distinctly different amyloid structures, termed polymorphs, and a given polymorph can reproduce itself by seeding. Amyloid polymorphs may be the molecular basis of prion strains. Whereas the Protein Data Bank contains some 100,000 globular protein and 3,000 membrane protein structures, only a few dozen amyloid protein structures have been determined, and most of these are short segments of full amyloid-forming proteins. Regardless, these amyloid structures illuminate the architecture of the amyloid state, including its stability and its capacity for formation of polymorphs.


Assuntos
Proteínas Amiloidogênicas/química , Proteínas Priônicas/química , Agregação Patológica de Proteínas/metabolismo , Motivos de Aminoácidos , Proteínas Amiloidogênicas/genética , Proteínas Amiloidogênicas/metabolismo , Animais , Microscopia Crioeletrônica , Expressão Gênica , Humanos , Ressonância Magnética Nuclear Biomolecular , Proteínas Priônicas/genética , Proteínas Priônicas/metabolismo , Agregação Patológica de Proteínas/genética , Agregação Patológica de Proteínas/patologia , Desnaturação Proteica , Multimerização Proteica , Estabilidade Proteica , Estrutura Secundária de Proteína , Difração de Raios X
4.
Cell ; 171(3): 615-627.e16, 2017 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-28942918

RESUMO

Polymerization and phase separation of proteins containing low-complexity (LC) domains are important factors in gene expression, mRNA processing and trafficking, and localization of translation. We have used solid-state nuclear magnetic resonance methods to characterize the molecular structure of self-assembling fibrils formed by the LC domain of the fused in sarcoma (FUS) RNA-binding protein. From the 214-residue LC domain of FUS (FUS-LC), a segment of only 57 residues forms the fibril core, while other segments remain dynamically disordered. Unlike pathogenic amyloid fibrils, FUS-LC fibrils lack hydrophobic interactions within the core and are not polymorphic at the molecular structural level. Phosphorylation of core-forming residues by DNA-dependent protein kinase blocks binding of soluble FUS-LC to FUS-LC hydrogels and dissolves phase-separated, liquid-like FUS-LC droplets. These studies offer a structural basis for understanding LC domain self-assembly, phase separation, and regulation by post-translational modification.


Assuntos
Proteína FUS de Ligação a RNA/química , Sequência de Aminoácidos , Humanos , Microscopia de Força Atômica , Microscopia Eletrônica de Transmissão , Modelos Moleculares , Ressonância Magnética Nuclear Biomolecular , Fosforilação , Domínios Proteicos , Proteína FUS de Ligação a RNA/metabolismo
5.
Cell ; 167(5): 1241-1251.e11, 2016 11 17.
Artigo em Inglês | MEDLINE | ID: mdl-27839865

RESUMO

The epidermal growth factor receptor (EGFR) represents one of the most common target proteins in anti-cancer therapy. To directly examine the structural and dynamical properties of EGFR activation by the epidermal growth factor (EGF) in native membranes, we have developed a solid-state nuclear magnetic resonance (ssNMR)-based approach supported by dynamic nuclear polarization (DNP). In contrast to previous crystallographic results, our experiments show that the ligand-free state of the extracellular domain (ECD) is highly dynamic, while the intracellular kinase domain (KD) is rigid. Ligand binding restricts the overall and local motion of EGFR domains, including the ECD and the C-terminal region. We propose that the reduction in conformational entropy of the ECD by ligand binding favors the cooperative binding required for receptor dimerization, causing allosteric activation of the intracellular tyrosine kinase.


Assuntos
Receptores ErbB/química , Receptores ErbB/metabolismo , Linhagem Celular Tumoral , Fator de Crescimento Epidérmico/metabolismo , Receptores ErbB/isolamento & purificação , Humanos , Membranas Intracelulares/química , Ressonância Magnética Nuclear Biomolecular , Multimerização Proteica , Termodinâmica , Vesículas Transportadoras/química
6.
Proc Natl Acad Sci U S A ; 121(9): e2316922121, 2024 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-38381790

RESUMO

The self-assembly of proteins into curved structures plays an important role in many cellular processes. One good example of this phenomenon is observed in the septum-forming protein (SepF), which forms polymerized structures with uniform curvatures. SepF is essential for regulating the thickness of the septum during bacteria cell division. In Bacillus subtilis, SepF polymerization involves two distinct interfaces, the ß-ß and α-α interfaces, which define the assembly unit and contact interfaces, respectively. However, the mechanism of curvature formation in this step is not yet fully understood. In this study, we employed solid-state NMR (SSNMR) to compare the structures of cyclic wild-type SepF assemblies with linear assemblies resulting from a mutation of G137 on the ß-ß interface. Our results demonstrate that while the sequence differences arise from the internal assembly unit, the dramatic changes in the shape of the assemblies depend on the α-α interface between the units. We further provide atomic-level insights into how the angular variation of the α2 helix on the α-α interface affects the curvature of the assemblies, using a combination of SSNMR, cryo-electron microscopy, and simulation methods. Our findings shed light on the shape control of protein assemblies and emphasize the importance of interhelical contacts in retaining curvature.


Assuntos
Citocinese , Microscopia Crioeletrônica , Polimerização , Divisão Celular , Mutação
7.
Proc Natl Acad Sci U S A ; 121(12): e2321540121, 2024 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-38483993

RESUMO

Nitrogen doped lutetium hydride has drawn global attention in the pursuit of room-temperature superconductivity near ambient pressure and temperature. However, variable synthesis techniques and uncertainty surrounding nitrogen concentration have contributed to extensive debate within the scientific community about this material and its properties. We used a solid-state approach to synthesize nitrogen doped lutetium hydride at high pressure and temperature (HPT) and analyzed the residual starting materials to determine its nitrogen content. High temperature oxide melt solution calorimetry determined the formation enthalpy of LuH1.96N0.02 (LHN) from LuH2 and LuN to be -28.4 ± 11.4 kJ/mol. Magnetic measurements indicated diamagnetism which increased with nitrogen content. Ambient pressure conductivity measurements observed metallic behavior from 5 to 350 K, and the constant and parabolic magnetoresistance changed with increasing temperature. High pressure conductivity measurements revealed that LHN does not exhibit superconductivity up to 26.6 GPa. We compressed LHN in a diamond anvil cell to 13.7 GPa and measured the Raman signal at each step, with no evidence of any phase transition. Despite the absence of superconductivity, a color change from blue to purple to red was observed with increasing pressure. Thus, our findings confirm the thermodynamic stability of LHN, do not support superconductivity, and provide insights into the origins of its diamagnetism.

8.
Proc Natl Acad Sci U S A ; 121(29): e2400898121, 2024 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-38980900

RESUMO

Precise electrochemical synthesis of commodity chemicals and fuels from CO2 building blocks provides a promising route to close the anthropogenic carbon cycle, in which renewable but intermittent electricity could be stored within the greenhouse gas molecules. Here, we report state-of-the-art CO2-to-HCOOH valorization performance over a multiscale optimized Cu-Bi cathodic architecture, delivering a formate Faradaic efficiency exceeding 95% within an aqueous electrolyzer, a C-basis HCOOH purity above 99.8% within a solid-state electrolyzer operated at 100 mA cm-2 for 200 h and an energy efficiency of 39.2%, as well as a tunable aqueous HCOOH concentration ranging from 2.7 to 92.1 wt%. Via a combined two-dimensional reaction phase diagram and finite element analysis, we highlight the role of local geometries of Cu and Bi in branching the adsorption strength for key intermediates like *COOH and *OCHO for CO2 reduction, while the crystal orbital Hamiltonian population analysis rationalizes the vital contribution from moderate binding strength of η2(O,O)-OCHO on Cu-doped Bi surface in promoting HCOOH electrosynthesis. The findings of this study not only shed light on the tuning knobs for precise CO2 valorization, but also provide a different research paradigm for advancing the activity and selectivity optimization in a broad range of electrosynthetic systems.

9.
Proc Natl Acad Sci U S A ; 121(23): e2401458121, 2024 Jun 04.
Artigo em Inglês | MEDLINE | ID: mdl-38809711

RESUMO

Patients with type 1 diabetes mellitus who are dependent on an external supply of insulin develop insulin-derived amyloidosis at the sites of insulin injection. A major component of these plaques is identified as full-length insulin consisting of the two chains A and B. While there have been several reports that characterize insulin misfolding and the biophysical properties of the fibrils, atomic-level information on the insulin fibril architecture remains elusive. We present here an atomic resolution structure of a monomorphic insulin amyloid fibril that has been determined using magic angle spinning solid-state NMR spectroscopy. The structure of the insulin monomer yields a U-shaped fold in which the two chains A and B are arranged in parallel to each other and are oriented perpendicular to the fibril axis. Each chain contains two ß-strands. We identify two hydrophobic clusters that together with the three preserved disulfide bridges define the amyloid core structure. The surface of the monomeric amyloid unit cell is hydrophobic implicating a potential dimerization and oligomerization interface for the assembly of several protofilaments in the mature fibril. The structure provides a starting point for the development of drugs that bind to the fibril surface and disrupt secondary nucleation as well as for other therapeutic approaches to attenuate insulin aggregation.


Assuntos
Amiloide , Insulina , Humanos , Amiloide/química , Amiloide/metabolismo , Insulina/química , Insulina/metabolismo , Modelos Moleculares , Interações Hidrofóbicas e Hidrofílicas , Diabetes Mellitus Tipo 1/tratamento farmacológico , Conformação Proteica , Espectroscopia de Ressonância Magnética
10.
Proc Natl Acad Sci U S A ; 121(33): e2401109121, 2024 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-39116136

RESUMO

Na5YSi4O12 (NYSO) is demonstrated as a promising electrolyte with high ionic conductivity and low activation energy for practical use in solid Na-ion batteries. Solid-state NMR was employed to identify the six types of coordination of Na+ ions and migration pathway, which is vital to master working mechanism and enhance performance. The assignment of each sodium site is clearly determined from high-quality 23Na NMR spectra by the aid of Density Functional Theory calculation. Well-resolved 23Na exchangespectroscopy and electrochemical tracer exchange spectra provide the first experimental evidence to show the existence of ionic exchange between sodium at Na5 and Na6 sites, revealing that Na transport route is possibly along three-dimensional chain of open channel-Na4-open channel. Variable-temperature NMR relaxometry is developed to evaluate Na jump rates and self-diffusion coefficient to probe the sodium-ion dynamics in NYSO. Furthermore, NYSO works well as a dual ion conductor in Na and Li metal batteries with Na3V2(PO4)3 and LiFePO4 as cathodes, respectively.

11.
Proc Natl Acad Sci U S A ; 121(10): e2316175121, 2024 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-38408247

RESUMO

The microtubule-associated protein tau aggregates into amyloid fibrils in Alzheimer's disease and other neurodegenerative diseases. In these tauopathies, tau is hyperphosphorylated, suggesting that this posttranslational modification (PTM) may induce tau aggregation. Tau is also phosphorylated in normal developing brains. To investigate how tau phosphorylation induces amyloid fibrils, here we report the atomic structures of two phosphomimetic full-length tau fibrils assembled without anionic cofactors. We mutated key Ser and Thr residues to Glu in two regions of the protein. One construct contains three Glu mutations at the epitope of the anti-phospho-tau antibody AT8 (AT8-3E tau), whereas the other construct contains four Glu mutations at the epitope of the antibody PHF1 (PHF1-4E tau). Solid-state NMR data show that both phosphomimetic tau mutants form homogeneous fibrils with a single set of chemical shifts. The AT8-3E tau rigid core extends from the R3 repeat to the C terminus, whereas the PHF1-4E tau rigid core spans R2, R3, and R4 repeats. Cryoelectron microscopy data show that AT8-3E tau forms a triangular multi-layered core, whereas PHF1-4E tau forms a triple-stranded core. Interestingly, a construct combining all seven Glu mutations exhibits the same conformation as PHF1-4E tau. Scalar-coupled NMR data additionally reveal the dynamics and shape of the fuzzy coat surrounding the rigid cores. These results demonstrate that specific PTMs induce structurally specific tau aggregates, and the phosphorylation code of tau contains redundancy.


Assuntos
Doença de Alzheimer , Proteínas tau , Humanos , Microscopia Crioeletrônica , Proteínas tau/metabolismo , Doença de Alzheimer/genética , Doença de Alzheimer/metabolismo , Anticorpos/genética , Epitopos , Processamento de Proteína Pós-Traducional , Fosforilação , Proteínas de Ligação a DNA/metabolismo , Proteínas do Grupo Polycomb/genética
12.
Proc Natl Acad Sci U S A ; 121(14): e2401982121, 2024 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-38536753

RESUMO

Photochemical valence bond isomerization of a crystalline Dewar benzene (DB) diacid monoanion salt with an acetophenone-linked piperazinium cation that serves as an intramolecular triplet energy sensitizer (DB-AcPh-Pz) exhibits a quantum chain reaction with as many as 450 product molecules per photon absorbed (Φ ≈ 450). By contrast, isomorphous crystals of the DB diacid monosalt of an ethylbenzene-linked piperazinium (DB-EtPh-Pz) lacking a triplet sensitizer showed a less impressive quantum yield of ca. Φ ≈ 22. To establish the critical importance of a triplet excited state carrier in the adiabatic photochemical reaction we prepared mixed crystals with DB-AcPh-Pz as a dilute triplet sensitizer guest in crystals of DB-EtPh-Pz. As expected from their high structural similarities, solid solutions were easily formed with the triplet sensitizer salt in the range of 0.1 to 10%. Experiments carried out under conditions where light is absorbed by the triplet sensitizer-linked DB-AcPh-Pz can be used to initiate a triplet state adiabatic reaction from 3DB-AcPh-Pz to 3HB*-AcPh-Pz, which can serve as a chain carrier and transfer energy to an unreacted DB-EtPh-Pz where exciton delocalization in the crystalline solid solution can help carry out an efficient energy transfer and enable a quantum chain employing the photoproduct as a triplet chain carrier. Excitation of mixed crystals with as little as 0.1% triplet sensitizer resulted in an extraordinarily high quantum yield Φ ≈ 517.

13.
Proc Natl Acad Sci U S A ; 121(6): e2312959121, 2024 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-38300865

RESUMO

The incorporation of multiple metal ions in metal-organic frameworks (MOFs) through one-pot synthesis can induce unique properties originating from specific atomic-scale spatial apportionment, but the extraction of this crucial information poses challenges. Herein, nondestructive solid-state NMR spectroscopy was used to discern the atomic-scale metal apportionment in a series of bulk Mg1-xCox-MOF-74 samples via identification and quantification of eight distinct arrangements of Mg/Co ions labeled with a 13C-carboxylate, relative to Co content. Due to the structural characteristics of metal-oxygen chains, the number of metal permutations is infinite for Mg1-xCox-MOF-74, making the resolution of atomic-scale metal apportionment particularly challenging. The results were then employed in density functional theory calculations to unravel the molecular mechanism underlying the macroscopic adsorption properties of several industrially significant gases. It is found that the incorporation of weak adsorption sites (Mg2+ for CO and Co2+ for CO2 adsorption) into the MOF structure counterintuitively boosts the gas adsorption energy on strong sites (Co2+ for CO and Mg2+ for CO2 adsorption). Such effect is significant even for Co2+ remote from Mg2+ in the metal-oxygen chain, resulting in a greater enhancement of CO adsorption across a broad composition range, while the enhancement of CO2 adsorption is restricted to Mg2+ with adjacent Co2+. Dynamic breakthrough measurements unambiguously verified the trend in gas adsorption as a function of metal composition. This research thus illuminates the interplay between atomic-scale structures and macroscopic gas adsorption properties in mixed-metal MOFs and derived materials, paving the way for developing superior functional materials.

14.
Proc Natl Acad Sci U S A ; 121(16): e2400203121, 2024 Apr 16.
Artigo em Inglês | MEDLINE | ID: mdl-38598338

RESUMO

Viral outbreaks can cause widespread disruption, creating the need for diagnostic tools that provide high performance and sample versatility at the point of use with moderate complexity. Current gold standards such as PCR and rapid antigen tests fall short in one or more of these aspects. Here, we report a label-free and amplification-free nanopore sensor platform that overcomes these challenges via direct detection and quantification of viral RNA in clinical samples from a variety of biological fluids. The assay uses an optofluidic chip that combines optical waveguides with a fluidic channel and integrates a solid-state nanopore for sensing of individual biomolecules upon translocation through the pore. High specificity and low limit of detection are ensured by capturing RNA targets on microbeads and collecting them by optical trapping at the nanopore location where targets are released and rapidly detected. We use this device for longitudinal studies of the viral load progression for Zika and Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) infections in marmoset and baboon animal models, respectively. The up to million-fold trapping-based target concentration enhancement enables amplification-free RNA quantification across the clinically relevant concentration range down to the assay limit of RT-qPCR as well as cases in which PCR failed. The assay operates across all relevant biofluids, including semen, urine, and whole blood for Zika and nasopharyngeal and throat swab, rectal swab, and bronchoalveolar lavage for SARS-CoV-2. The versatility, performance, simplicity, and potential for full microfluidic integration of the amplification-free nanopore assay points toward a unique approach to molecular diagnostics for nucleic acids, proteins, and other targets.


Assuntos
Nanoporos , Infecção por Zika virus , Zika virus , Animais , RNA Viral/genética , RNA Viral/metabolismo , SARS-CoV-2/genética , SARS-CoV-2/metabolismo , Primatas/genética , Zika virus/genética , Sensibilidade e Especificidade , Técnicas de Amplificação de Ácido Nucleico
15.
Proc Natl Acad Sci U S A ; 121(8): e2301053120, 2024 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-38346186

RESUMO

While low-temperature Nuclear Magnetic Resonance (NMR) holds great promise for the analysis of unstable samples and for sensitizing NMR detection, spectral broadening in frozen protein samples is a common experimental challenge. One hypothesis explaining the additional linewidth is that a variety of conformations are in rapid equilibrium at room temperature and become frozen, creating an inhomogeneous distribution at cryogenic temperatures. Here, we investigate conformational heterogeneity by measuring the backbone torsion angle (Ψ) in Escherichia coli Dihydrofolate Reductase (DHFR) at 105 K. Motivated by the particularly broad N chemical shift distribution in this and other examples, we modified an established NCCN Ψ experiment to correlate the chemical shift of Ni+1 to Ψi. With selective 15N and 13C enrichment of Ile, only the unique I60-I61 pair was expected to be detected in 13C'-15N correlation spectrum. For this unique amide, we detected three different conformation basins based on dispersed chemical shifts. Backbone torsion angles Ψ were determined for each basin: 114 ± 7° for the major peak and 150 ± 8° and 164 ± 16° for the minor peaks as contrasted with 118° for the X-ray crystal structure (and 118° to 130° for various previously reported structures). These studies support the hypothesis that inhomogeneous distributions of protein backbone torsion angles contribute to the lineshape broadening in low-temperature NMR spectra.


Assuntos
Temperatura Baixa , Proteínas , Temperatura , Espectroscopia de Ressonância Magnética , Conformação Proteica , Proteínas/química , Ressonância Magnética Nuclear Biomolecular
16.
Proc Natl Acad Sci U S A ; 120(44): e2310067120, 2023 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-37878719

RESUMO

The microtubule-associated protein tau aggregates into neurofibrillary tangles in Alzheimer's disease (AD). The main type of aggregates, the paired helical filaments (PHF), incorporate about 20% of the full-length protein into the rigid core. Recently, cryo-electron microscopy data showed that a protease-resistant fragment of tau (residues 297-391) self-assembles in vitro in the presence of divalent cations to form twisted filaments whose molecular structure resembles that of AD PHF tau [S. Lövestam et al., Elife 11, e76494 (2022)]. To investigate whether this tau construct is uniquely predisposed to this morphology and structure, we fibrillized tau (297-391) under the reported conditions and determined its structure using solid-state NMR spectroscopy. Unexpectedly, the protein assembled predominantly into nontwisting ribbons whose rigid core spans residues 305-357. This rigid core forms a ß-arch that turns at residues 322CGS324. Two protofilaments stack together via a long interface that stretches from G323 to I354. Together, these two protofilaments form a four-layered ß-sheet core whose sidechains are stabilized by numerous polar and hydrophobic interactions. This structure gives insight into the fibril morphologies and molecular conformations that can be adopted by this protease-resistant core of AD tau under different pH and ionic conditions.


Assuntos
Proteínas tau , Humanos , Doença de Alzheimer/metabolismo , Microscopia Crioeletrônica , Citoesqueleto/metabolismo , Emaranhados Neurofibrilares/metabolismo , Peptídeo Hidrolases , Proteínas tau/química , Proteínas tau/metabolismo
17.
Proc Natl Acad Sci U S A ; 120(43): e2308741120, 2023 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-37862383

RESUMO

Macromolecules bearing open-shell entities offer unique transport properties for both electronic and spintronic devices. This work demonstrates that, unlike their conjugated polymer counterparts, the charge carriers in radical polymers (i.e., macromolecules with nonconjugated backbones and with stable open-shell sites present at their pendant groups) are singlet cations, which opens significant avenues for manipulating macromolecular design for advanced solid-state transport in these highly transparent conductors. Despite this key point, magnetoresistive effects are present in radical polymer thin films under applied magnetic fields due to the presence of impurity sites in low (i.e., <1%) concentrations. Additionally, thermal annealing of poly(4-glycidyloxy-2,2,6,6- tetramethylpiperidine-1-oxyl) (PTEO), a nonconjugated polymer with stable open-shell pendant groups, facilitated better electron exchange and pairwise spin interactions resulting in an unexpected magnetoresistance signal at relatively low field strengths (i.e., <2 T). The addition of 4-hydroxy-2,2,6,6-tetramethylpiperidin-N-oxy (TEMPO-OH), a paramagnetic species, increased the magnitude of the MR effect when the small molecule was added to the radical polymer matrix. These macroscopic experimental observables are explained using computational approaches that detail the fundamental molecular principles. This intrinsic localized charge transport behavior differs from the current state of the art regarding closed-shell conjugated macromolecules, and it opens an avenue towards next-generation transport in organic electronic materials.

18.
Proc Natl Acad Sci U S A ; 120(6): e2212003120, 2023 02 07.
Artigo em Inglês | MEDLINE | ID: mdl-36719915

RESUMO

While establishing an invasive infection, the dormant conidia of Aspergillus fumigatus transit through swollen and germinating stages, to form hyphae. During this morphotype transition, the conidial cell wall undergoes dynamic remodeling, which poses challenges to the host immune system and antifungal drugs. However, such cell wall reorganization during conidial germination has not been studied so far. Here, we explored the molecular rearrangement of Aspergillus fumigatus cell wall polysaccharides during different stages of germination. We took advantage of magic-angle spinning NMR to investigate the cell wall polysaccharides, without employing any destructive method for sample preparation. The breaking of dormancy was associated with a significant change in the molar ratio between the major polysaccharides ß-1,3-glucan and α-1,3-glucan, while chitin remained equally abundant. The use of various polarization transfers allowed the detection of rigid and mobile polysaccharides; the appearance of mobile galactosaminogalactan was a molecular hallmark of germinating conidia. We also report for the first time highly abundant triglyceride lipids in the mobile matrix of conidial cell walls. Water to polysaccharides polarization transfers revealed an increased surface exposure of glucans during germination, while chitin remained embedded deeper in the cell wall, suggesting a molecular compensation mechanism to keep the cell wall rigidity. We complement the NMR analysis with confocal and atomic force microscopies to explore the role of melanin and RodA hydrophobin on the dormant conidial surface. Exemplified here using Aspergillus fumigatus as a model, our approach provides a powerful tool to decipher the molecular remodeling of fungal cell walls during their morphotype switching.


Assuntos
Aspergillus fumigatus , Proteínas Fúngicas , Aspergillus fumigatus/metabolismo , Esporos Fúngicos/metabolismo , Proteínas Fúngicas/metabolismo , Polissacarídeos/metabolismo , Quitina/metabolismo , Glucanos/metabolismo , Parede Celular/metabolismo
19.
Proc Natl Acad Sci U S A ; 120(11): e2218831120, 2023 03 14.
Artigo em Inglês | MEDLINE | ID: mdl-36893281

RESUMO

Fibrils formed by the 42-residue amyloid-ß peptide (Aß42), a main component of amyloid deposits in Alzheimer's disease (AD), are known to be polymorphic, i.e., to contain multiple possible molecular structures. Previous studies of Aß42 fibrils, including fibrils prepared entirely in vitro or extracted from brain tissue and using solid-state NMR (ssNMR) or cryogenic electron microscopy (cryo-EM) methods, have found polymorphs with differences in amino acid sidechain orientations, lengths of structurally ordered segments, and contacts between cross-ß subunit pairs within a single filament. Despite these differences, Aß42 molecules adopt a common S-shaped conformation in all previously described high-resolution Aß42 fibril structures. Here we report two cryo-EM-based structures of Aß42 fibrils that are qualitatively different, in samples derived from AD brain tissue by seeded growth. In type A fibrils, residues 12 to 42 adopt a ν-shaped conformation, with both intra-subunit and intersubunit hydrophobic contacts to form a compact core. In type B fibrils, residues 2 to 42 adopt an υ-shaped conformation, with only intersubunit contacts and internal pores. Type A and type B fibrils have opposite helical handedness. Cryo-EM density maps and molecular dynamics simulations indicate intersubunit K16-A42 salt bridges in type B fibrils and partially occupied K28-A42 salt bridges in type A fibrils. The coexistence of two predominant polymorphs, with differences in N-terminal dynamics, is supported by ssNMR data, as is faithful propagation of structures from first-generation to second-generation brain-seeded Aß42 fibril samples. These results demonstrate that Aß42 fibrils can exhibit a greater range of structural variations than seen in previous studies.


Assuntos
Doença de Alzheimer , Peptídeos beta-Amiloides , Humanos , Peptídeos beta-Amiloides/metabolismo , Doença de Alzheimer/metabolismo , Espectroscopia de Ressonância Magnética , Encéfalo/metabolismo , Conformação Molecular , Amiloide/química , Fragmentos de Peptídeos/metabolismo
20.
Proc Natl Acad Sci U S A ; 120(15): e2300197120, 2023 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-37018192

RESUMO

Composite-polymer-electrolytes (CPEs) embedded with advanced filler materials offer great promise for fast and preferential Li+ conduction. The filler surface chemistry determines the interaction with electrolyte molecules and thus critically regulates the Li+ behaviors at the interfaces. Herein, we probe into the role of electrolyte/filler interfaces (EFI) in CPEs and promote Li+ conduction by introducing an unsaturated coordination Prussian blue analog (UCPBA) filler. Combining scanning transmission X-ray microscope stack imaging studies and first-principle calculations, fast Li+ conduction is revealed only achievable at a chemically stable EFI, which can be established by the unsaturated Co-O coordination in UCPBA to circumvent the side reactions. Moreover, the as-exposed Lewis-acid metal centers in UCPBA efficiently attract the Lewis-base anions of Li salts, which facilitates the Li+ disassociation and enhances its transference number (tLi+). Attributed to these superiorities, the obtained CPEs realize high room-temperature ionic conductivity up to 0.36 mS cm-1 and tLi+ of 0.6, enabling an excellent cyclability of lithium metal electrodes over 4,000 h as well as remarkable capacity retention of 97.6% over 180 cycles at 0.5 C for solid-state lithium-sulfur batteries. This work highlights the crucial role of EFI chemistry in developing highly conductive CPEs and high-performance solid-state batteries.

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