PML nuclear bodies (PML-NBs) are enigmatic structures of the cell nucleus that act as key mediators of intrinsic immunity against viral pathogens. PML itself is a member of the E3-ligase TRIM family ...of proteins that regulates a variety of innate immune signaling pathways. Consequently, viruses have evolved effector proteins to modify PML-NBs; however, little is known concerning structure-function relationships of viral antagonists. The herpesvirus human cytomegalovirus (HCMV) expresses the abundant immediate-early protein IE1 that colocalizes with PML-NBs and induces their dispersal, which correlates with the antagonization of NB-mediated intrinsic immunity. Here, we delineate the molecular basis for this antagonization by presenting the first crystal structure for the evolutionary conserved primate cytomegalovirus IE1 proteins. We show that IE1 consists of a globular core (IE1CORE) flanked by intrinsically disordered regions. The 2.3 Å crystal structure of IE1CORE displays an all α-helical, femur-shaped fold, which lacks overall fold similarity with known protein structures, but shares secondary structure features recently observed in the coiled-coil domain of TRIM proteins. Yeast two-hybrid and coimmunoprecipitation experiments demonstrate that IE1CORE binds efficiently to the TRIM family member PML, and is able to induce PML deSUMOylation. Intriguingly, this results in the release of NB-associated proteins into the nucleoplasm, but not of PML itself. Importantly, we show that PML deSUMOylation by IE1CORE is sufficient to antagonize PML-NB-instituted intrinsic immunity. Moreover, co-immunoprecipitation experiments demonstrate that IE1CORE binds via the coiled-coil domain to PML and also interacts with TRIM5α We propose that IE1CORE sequesters PML and possibly other TRIM family members via structural mimicry using an extended binding surface formed by the coiled-coil region. This mode of interaction might render the antagonizing activity less susceptible to mutational escape.
Poly-3-hydroxybutyrate (PHB) is a polyester with thermoplastic properties that is naturally occurring and produced by such bacteria as Ralstonia eutropha H16 and Bacillus megaterium. In contrast to ...currently utilized plastics and most synthetic polymers, PHB is biodegradable, and its production is not dependent on fossil resources making this bioplastic interesting for various industrial applications.
In this study, we report on introducing the bacterial PHB pathway of R. eutropha H16 into the diatom Phaeodactylum tricornutum, thereby demonstrating for the first time that PHB production is feasible in a microalgal system. Expression of the bacterial enzymes was sufficient to result in PHB levels of up to 10.6% of algal dry weight. The bioplastic accumulated in granule-like structures in the cytosol of the cells, as shown by light and electron microscopy.
Our studies demonstrate the great potential of microalgae like the diatom P. tricornutum to serve as solar-powered expression factories and reveal great advantages compared to plant based production systems.
Impact statement
Methane oxidizing microbes play a key role in reducing the emission of this potent greenhouse gas to the atmosphere. The known versatility of the recently discovered anaerobic ...Methylomirabilota methanotrophs is limited. Here, we report a novel uncultured Methylomirabilis species, Candidatus Methylomirabilis iodofontis, with the genetic potential of iodate respiration from biofilm in iodine‐rich cavern spring water. Star‐like cells resembling Methylomirabilis oxyfera were directly observed from the biofilm and a high‐quality metagenome‐assembled genome (MAG) of Ca. M. iodofontis was assembled. In addition to oxygenic denitrification and aerobic methane oxidation pathways, the M. iodofontis MAG also indicated its iodate‐reducing potential, a capability that would enable the bacterium to use iodate other than nitrite as an electron acceptor, a hitherto unrecognized metabolic potential of Methylomirabilota methanotrophs. The results advance the current understanding of the ecophysiology of anaerobic Methylomirabilota methanotrophs and may suggest an additional methane sink, especially in iodate‐rich ecosystems.
Extracellular vesicles (EVs) are endogenous membrane‐derived vesicles that shuttle bioactive molecules between glia and neurons, thereby promoting neuronal survival and plasticity in the central ...nervous system (CNS) and contributing to neurodegenerative conditions. Although EVs hold great potential as CNS theranostic nanocarriers, the specific molecular factors that regulate neuronal EV uptake and release are currently unknown. A combination of patch‐clamp electrophysiology and pH‐sensitive dye imaging is used to examine stimulus‐evoked EV release in individual neurons in real time. Whereas spontaneous electrical activity and the application of a high‐frequency stimulus induce a slow and prolonged fusion of multivesicular bodies (MVBs) with the plasma membrane (PM) in a subset of cells, the neurotrophic factor basic fibroblast growth factor (bFGF) greatly increases the rate of stimulus‐evoked MVB‐PM fusion events and, consequently, the abundance of EVs in the culture medium. Proteomic analysis of neuronal EVs demonstrates bFGF increases the abundance of the v‐SNARE vesicle‐associated membrane protein 3 (VAMP3, cellubrevin) on EVs. Conversely, knocking‐down VAMP3 in cultured neurons attenuates the effect of bFGF on EV release. The results determine the temporal characteristics of MVB‐PM fusion in hippocampal neurons and reveal a new function for bFGF signaling in controlling neuronal EV release.
Extracellular vesicles (EVs) are endogenous membrane‐derived vesicles that shuttle biomolecules from cell to cell. The molecular mechanisms that modulate EV release in the central nervous system are poorly understood. Here, it is demonstrated that fibroblast growth factor 2 increases the expression of VAMP3/cellubrevin to enhance the release of EVs from hippocampal neurons.
Diatoms are unicellular organisms evolved by secondary endosymbiosis. Although studied in many aspects, the functions of vacuolar-like structures of these organisms are rarely investigated. One of ...these structures is a dominant central vacuole-like compartment with a marbled phenotype, which is supposed to represent a chrysolaminarin-storing and carbohydrate mobilization compartment. However, other functions as well as targeting of proteins to this compartment are not shown experimentally. In order to study trafficking of membrane proteins to the vacuolar membrane, we scanned the genome for intrinsic vacuolar membrane proteins and used one representative for targeting studies. Our work led to the identification of several proteins located in the vacuolar membrane as well as the sub-compartmentalized localization of one protein. In addition, we show that a di-leucine-based motif is an important signal for correct targeting to the central vacuole of diatoms, like it is in plants.
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