RESUMEN
The dynamic regulation of mitochondria shape via fission and fusion is critical for cellular responses to stimuli. In homeostatic cells, two modes of mitochondrial fission, midzone and peripheral, provide a decision fork between either proliferation or clearance of mitochondria. However, the relationship between specific mitochondria shapes and functions remains unclear in many biological contexts. While commonly associated with decreased bioenergetics, fragmented mitochondria paradoxically exhibit elevated respiration in several disease states, including infection with the prevalent pathogen human cytomegalovirus (HCMV) and metastatic melanoma. Here, incorporating super-resolution microscopy with mass spectrometry and metabolic assays, we use HCMV infection to establish a molecular mechanism for maintaining respiration within a fragmented mitochondria population. We establish that HCMV induces fragmentation through peripheral mitochondrial fission coupled with suppression of mitochondria fusion. Unlike uninfected cells, the progeny of peripheral fission enter mitochondria-ER encapsulations (MENCs) where they are protected from degradation and bioenergetically stabilized during infection. MENCs also stabilize pro-viral inter-mitochondria contacts (IMCs), which electrochemically link mitochondria and promote respiration. Demonstrating a broader relevance, we show that the fragmented mitochondria within metastatic melanoma cells also form MENCs. Our findings establish a mechanism where mitochondria fragmentation can promote increased respiration, a feature relevant in the context of human diseases.
Asunto(s)
Citomegalovirus , Retículo Endoplásmico , Metabolismo Energético , Mitocondrias , Dinámicas Mitocondriales , Humanos , Mitocondrias/metabolismo , Citomegalovirus/fisiología , Retículo Endoplásmico/metabolismo , Infecciones por Citomegalovirus/metabolismo , Infecciones por Citomegalovirus/virología , Melanoma/metabolismo , Melanoma/patología , Melanoma/virología , Línea Celular TumoralRESUMEN
The viral nuclear egress complex (NEC) allows herpesvirus capsids to escape from the nucleus without compromising the nuclear envelope integrity. The NEC lattice assembles on the inner nuclear membrane and mediates the budding of nascent nucleocapsids into the perinuclear space and their subsequent release into the cytosol. Its essential role makes it a potent antiviral target, necessitating structural information in the context of a cellular infection. Here we determined structures of NEC-capsid interfaces in situ using electron cryo-tomography, showing a substantial structural heterogeneity. In addition, while the capsid is associated with budding initiation, it is not required for curvature formation. By determining the NEC structure in several conformations, we show that curvature arises from an asymmetric assembly of disordered and hexagonally ordered lattice domains independent of pUL25 or other viral capsid vertex components. Our results advance our understanding of the mechanism of nuclear egress in the context of a living cell.
Asunto(s)
Cápside , Núcleo Celular , Microscopía por Crioelectrón , Membrana Nuclear , Liberación del Virus , Núcleo Celular/metabolismo , Núcleo Celular/virología , Humanos , Membrana Nuclear/metabolismo , Cápside/metabolismo , Proteínas de la Cápside/metabolismo , Proteínas de la Cápside/genética , Nucleocápside/metabolismo , Tomografía con Microscopio Electrónico , Proteínas Virales/metabolismo , Proteínas Virales/genética , Herpesviridae/fisiología , Herpesviridae/genéticaRESUMEN
Due to its asymmetric shape, size and compactness, the structure of the infectious mature virus (MV) of vaccinia virus (VACV), the best-studied poxvirus, remains poorly understood. Instead, subviral particles, in particular membrane-free viral cores, have been studied with cryo-electron microscopy. Here, we compared viral cores obtained by detergent stripping of MVs with cores in the cellular cytoplasm, early in infection. We focused on the prominent palisade layer on the core surface, combining cryo-electron tomography, subtomogram averaging and AlphaFold2 structure prediction. We showed that the palisade is composed of densely packed trimers of the major core protein A10. Trimers display a random order and their classification indicates structural flexibility. A10 on cytoplasmic cores is organized in a similar manner, indicating that the structures obtained in vitro are physiologically relevant. We discuss our results in the context of the VACV replicative cycle, and the assembly and disassembly of the infectious MV.
Asunto(s)
Microscopía por Crioelectrón , Virus Vaccinia , Virus Vaccinia/ultraestructura , Humanos , Multimerización de Proteína , Tomografía con Microscopio Electrónico , Modelos Moleculares , Virión/ultraestructura , Virión/metabolismoRESUMEN
Microtubules are a ubiquitous eukaryotic cytoskeletal element typically consisting of 13 protofilaments arranged in a hollow cylinder. This arrangement is considered the canonical form and is adopted by most organisms, with rare exceptions. Here, we use in situ electron cryo-tomography and subvolume averaging to analyse the changing microtubule cytoskeleton of Plasmodium falciparum, the causative agent of malaria, throughout its life cycle. Unexpectedly, different parasite forms have distinct microtubule structures coordinated by unique organising centres. In merozoites, the most widely studied form, we observe canonical microtubules. In migrating mosquito forms, the 13 protofilament structure is further reinforced by interrupted luminal helices. Surprisingly, gametocytes contain a wide distribution of microtubule structures ranging from 13 to 18 protofilaments, doublets and triplets. Such a diversity of microtubule structures has not been observed in any other organism to date and is likely evidence of a distinct role in each life cycle form. This data provides a unique view into an unusual microtubule cytoskeleton of a relevant human pathogen.
Asunto(s)
Culicidae , Pabellón Auricular , Parásitos , Humanos , Animales , Microtúbulos , CitoesqueletoRESUMEN
Mimivirus is the prototype of the Mimiviridae family of giant dsDNA viruses. Little is known about the organization of the 1.2 Mb genome inside the membrane-limited nucleoid filling the ~0.5 µm icosahedral capsids. Cryo-electron microscopy, cryo-electron tomography, and proteomics revealed that it is encased into a ~30-nm diameter helical protein shell surprisingly composed of two GMC-type oxidoreductases, which also form the glycosylated fibrils decorating the capsid. The genome is arranged in 5- or 6-start left-handed super-helices, with each DNA-strand lining the central channel. This luminal channel of the nucleoprotein fiber is wide enough to accommodate oxidative stress proteins and RNA polymerase subunits identified by proteomics. Such elegant supramolecular organization would represent a remarkable evolutionary strategy for packaging and protecting the genome, in a state ready for immediate transcription upon unwinding in the host cytoplasm. The parsimonious use of the same protein in two unrelated substructures of the virion is unexpected for a giant virus with thousand genes at its disposal.
Asunto(s)
Virus Gigantes , Mimiviridae , Cápside/metabolismo , Microscopía por Crioelectrón/métodos , Genoma Viral , Virus Gigantes/genética , Mimiviridae/genética , Nucleoproteínas/genética , Nucleoproteínas/metabolismo , Oxidorreductasas/metabolismoRESUMEN
The combination of super-resolution fluorescence microscopy and electron microscopy at ambient temperatures has become an established technique and a broad variety of modalities are now available to the cell biology community. In contrast, correlative cryogenic super-resolution fluorescence and electron microscopy (super-resolution cryo-CLEM) is just emerging. Aside from technical challenges, one of the major issues is the risk of devitrification of the specimen caused by the laser intensities required for super-resolution imaging. Cryo-SOFI (cryogenic super-resolution optical fluctuation imaging) allows the reconstruction of super-resolution images at particularly low laser intensities. It is fully compatible with the standard sample preparation for cryogenic electron microscopy (cryo-EM) and fairly easy to implement in any standard cryogenic fluorescence microscope.
Asunto(s)
Electrones , Luz , Microscopía por Crioelectrón , Microscopía Electrónica , Microscopía FluorescenteRESUMEN
Electron cryotomography (cryoET), an electron cryomicroscopy (cryoEM) modality, has changed our understanding of biological function by revealing the native molecular details of membranes, viruses, and cells. However, identification of individual molecules within tomograms from cryoET is challenging because of sample crowding and low signal-to-noise ratios. Here, we present a tagging strategy for cryoET that precisely identifies individual protein complexes in tomograms without relying on metal clusters. Our method makes use of DNA origami to produce "molecular signposts" that target molecules of interest, here via fluorescent fusion proteins, providing a platform generally applicable to biological surfaces. We demonstrate the specificity of signpost origami tags (SPOTs) in vitro as well as their suitability for cryoET of membrane vesicles, enveloped viruses, and the exterior of intact mammalian cells.
Asunto(s)
Membrana Celular/ultraestructura , Microscopía por Crioelectrón , ADN/ultraestructura , Tomografía con Microscopio Electrónico , Animales , Aptámeros de Nucleótidos/química , Fenómenos Biofísicos , Línea Celular , Femenino , Fluorescencia , Humanos , Nanopartículas/ultraestructuraRESUMEN
Viruses are obligatory intracellular parasites that reprogram host cells upon infection to produce viral progeny. Here, we review recent structural insights into virus-host interactions in bacteria, archaea, and eukaryotes unveiled by cellular electron cryo-tomography (cryoET). This advanced three-dimensional imaging technique of vitreous samples in near-native state has matured over the past two decades and proven powerful in revealing molecular mechanisms underlying viral replication. Initial studies were restricted to cell peripheries and typically focused on early infection steps, analyzing surface proteins and viral entry. Recent developments including cryo-thinning techniques, phase-plate imaging, and correlative approaches have been instrumental in also targeting rare events inside infected cells. When combined with advances in dedicated image analyses and processing methods, details of virus assembly and egress at (sub)nanometer resolution were uncovered. Altogether, we provide a historical and technical perspective and discuss future directions and impacts of cryoET for integrative structural cell biology analyses of viruses.
Asunto(s)
Microscopía por Crioelectrón/métodos , Tomografía con Microscopio Electrónico/métodos , Interacciones Microbiota-Huesped , Imagenología Tridimensional/métodos , Humanos , Procesamiento de Imagen Asistido por Computador , Imagenología Tridimensional/instrumentación , Replicación Viral , Virus/ultraestructuraRESUMEN
Perforin-2 (MPEG1) is thought to enable the killing of invading microbes engulfed by macrophages and other phagocytes, forming pores in their membranes. Loss of perforin-2 renders individual phagocytes and whole organisms significantly more susceptible to bacterial pathogens. Here, we reveal the mechanism of perforin-2 activation and activity using atomic structures of pre-pore and pore assemblies, high-speed atomic force microscopy, and functional assays. Perforin-2 forms a pre-pore assembly in which its pore-forming domain points in the opposite direction to its membrane-targeting domain. Acidification then triggers pore formation, via a 180° conformational change. This novel and unexpected mechanism prevents premature bactericidal attack and may have played a key role in the evolution of all perforin family proteins.
Asunto(s)
Bacterias/inmunología , Evolución Molecular , Profilinas/ultraestructura , Conformación Proteica , Animales , Bacterias/patogenicidad , Humanos , Inmunidad Innata/inmunología , Macrófagos/química , Macrófagos/microbiología , Mamíferos/microbiología , Ratones , Fagocitos/química , Fagocitos/microbiología , Profilinas/químicaRESUMEN
Rabies virus is an important zoonotic pathogen. Its bullet shaped particle contains a helical nucleocapsid. We used cryo-electron tomography and subsequent subtomogram averaging to determine the structure of its ribonucleoprotein. The resulting electron density map allowed for confident fitting of the N-protein crystal structure, indicating that interactions between neighbouring N-proteins are only mediated by N- and C-terminal protruding subdomains (aa 1-27 and aa 355-372). Additional connecting densities, likely stabilizing the ribonucleoprotein complex, are present between neighbouring M-protein densities on the same helical turn and between M- and N-protein densities located on neighbouring helical turns, but not between M-proteins of different turns, as is observed for the related Vesicular stomatitis virus (VSV). This insight into the architecture of the rabies virus nucleocapsid highlights the surprising structural divergence of large biological assemblies even if the building blocks - here exemplified by VSV M- and N-protein - are structurally closely related.
Asunto(s)
Microscopía por Crioelectrón/métodos , Virus de la Rabia/metabolismo , Virus de la Rabia/ultraestructura , Rabia/virología , Ribonucleoproteínas/metabolismo , Ribonucleoproteínas/ultraestructura , Virión/ultraestructura , Células HEK293 , Humanos , ARN Viral/análisis , ARN Viral/metabolismoRESUMEN
Correlative light and electron cryo-microscopy (cryo-CLEM) combines information from the specific labeling of fluorescence cryo-microscopy (cryo-FM) with the high resolution in environmental context of electron cryo-microscopy (cryo-EM). Exploiting super-resolution methods for cryo-FM is advantageous, as it enables the identification of rare events within the environmental background of cryo-EM at a sensitivity and resolution beyond that of conventional methods. However, due to the need for relatively high laser intensities, current super-resolution cryo-CLEM methods require cryo-protectants or support films which can severely reduce image quality in cryo-EM and are not compatible with many samples, such as mammalian cells. Here, we introduce cryogenic super-resolution optical fluctuation imaging (cryo-SOFI), a low-dose super-resolution imaging scheme based on the SOFI principle. As cryo-SOFI does not require special sample preparation, it is fully compatible with conventional cryo-EM specimens, and importantly, it does not affect the quality of cryo-EM imaging. By applying cryo-SOFI to a variety of biological application examples, we demonstrate resolutions up to â¼135 nm, an improvement of up to three times compared with conventional cryo-FM, while maintaining the specimen in a vitrified state for subsequent cryo-EM. Cryo-SOFI presents a general solution to the problem of specimen devitrification in super-resolution cryo-CLEM. It does not require a complex optical setup and can easily be implemented in any existing cryo-FM system.
Asunto(s)
Microscopía por Crioelectrón/métodos , Animales , Línea Celular , Retículo Endoplásmico/ultraestructura , Humanos , Microscopía Fluorescente , Mitocondrias/ultraestructuraRESUMEN
Mechanosensitive channels protect bacteria against lysis caused by a sudden drop in osmolarity in their surroundings. Besides the channel of large conductance (MscL) and small conductance (MscS), Escherichia coli has five additional paralogs of MscS that are functional and widespread in the bacterial kingdom. Here, we present the structure of YnaI by cryo-electron microscopy to a resolution of 13 Å. While the cytosolic vestibule is structurally similar to that in MscS, additional density is seen in the transmembrane (TM) region consistent with the presence of two additional TM helices predicted for YnaI. The location of this density suggests that the extra TM helices are tilted, which could induce local membrane curvature extending the tension-sensing paddles seen in MscS. Off-center lipid-accessible cavities are seen that resemble gaps between the sensor paddles in MscS. The conservation of the tapered shape and the cavities in YnaI suggest a mechanism similar to that of MscS.