The dynamin superfamily

Endogenous interactomes of MFN1 and MFN2 provide novel insights into interorganelle communication and autophagy

MFN1 (mitofusin 1) and MFN2 are key players in mitochondrial fusion, endoplasmic reticulum (ER)-mitochondria juxtaposition, and macroautophagy/autophagy. However, the mechanisms by which these proteins participate in these processes are poorly understood. Here, we studied the interactomes of these two proteins by using CRISPR-Cas9 technology to insert an HA-tag at the C terminus of MFN1 and MFN2, and thus generating HeLa cell lines that endogenously expressed MFN1-HA or MFN2-HA. HA-affinity isolation followed by mass spectrometry identified potential interactors of MFN1 and MFN2. A substantial proportion of interactors were common for MFN1 and MFN2 and were regulated by nutrient deprivation. We validated novel ER and endosomal partners of MFN1 and/or MFN2 with a potential role in interorganelle communication. We characterized RAB5C (RAB5C, member RAS oncogene family) as an endosomal modulator of mitochondrial homeostasis, and SLC27A2 (solute carrier family 27 (fatty acid transporter), member 2) as a novel partner of MFN2 relevant in autophagy. We conclude that MFN proteins participate in nutrient-modulated pathways involved in organelle communication and autophagy.Abbreviations: ACTB: actin, beta; ATG2: autophagy related 2; ATG5: autophagy related 5; ATG12: autophagy related 12; ATG14: autophagy related 14; ATG16L1: autophagy related 16 like 1; Baf A1: bafilomycin A1; BECN1: beclin 1, autophagy related; BFDR: Bayesian false discovery rate; Cas9: CRISPR-associated endonuclease Cas9; CRISPR: clustered regularly interspaced short palindromic repeats; DNM1L/DRP1: dynamin 1-like; ER: endoplasmic reticulum; Faa1: fatty acid activation 1; FC: fold change; FDR: false discovery rate; FIS1: fission, mitochondrial 1; GABARAP: gamma-aminobutyric acid receptor associated protein; GABARAPL2: GABA type A receptor associated protein like 2; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; HA: hemagglutinin; KO: knockout; LIR: LC3-interacting region; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MARCHF5: membrane associated ring-CH-type finger 5; MDVs: mitochondria-derived vesicles; MFN1: mitofusin 1; MFN2: mitofusin 2; NDFIP2: Nedd4 family interacting protein 2; OMM: outer mitochondrial membrane; OPA1: OPA1, mitochondrial dynamin like GTPase; OXPHOS: oxidative phosphorylation; PE: phosphatidylethanolamine; PINK1: PTEN induced putative kinase 1; PS: phosphatidylserine; RAB5C: RAB5C, member RAS oncogene family; S100A8: S100 calcium binding protein A8 (calgranulin A); S100A9: S100 calcium binding protein A9 (calgranulin B); SLC27A2: solute carrier family 27 (fatty acid transporter), member 2; TIMM44: translocase of inner mitochondrial membrane 44; TOMM20: translocase of outer mitochondrial membrane 20; ULK1: unc-51 like kinase 1; VCL: vinculin; VDAC1: voltage-dependent anion channel 1; WT: wild type.

Phylogenomics and adaptive evolution of the Colletotrichum gloeosporioides species complex

The Colletotrichum gloeosporioides species complex (CGSC) is one of the most devastating fungal phytopathogens, and is composed of three main clades: Kahawae, Musae, and Theobromicola. Despite the diversity of CGSC, there is limited understanding on their evolutionary mechanisms. By analysing 49 newly assembled genomes, we found that the expansion of transposable elements, especially long terminal repeat retrotransposons, facilitates the expansion of genome size and genetic variation. In-depth analyses suggested that an intra-chromosomal inversion may have been the driving force behind the divergence of Kahawae clade from its ancestor. Within the Kahawae clade, the narrow-hosted quarantine species C. kahawae has undergone extensive chromosomal rearrangements mediated by repetitive sequences, generating highly dynamic lineage-specific genomic regions compared to the closely related broad-hosted species C. cigarro. The findings of this study highlight the role of chromosomal rearrangements in promoting genetic diversification and host adaptation, and provide new perspectives for understanding the evolution of phytopathogenic fungi.

Bringing together but staying apart: decisive differences in animal and fungal mitochondrial inner membrane fusion

Mitochondria are dynamic and plastic, undergoing continuous fission and fusion and rearrangement of their bioenergetic sub-compartments called cristae. These fascinating processes are best understood in animal and fungal models, which are taxonomically grouped together in the expansive Opisthokonta supergroup. In opisthokonts, crista remodelling and inner membrane fusion are linked by dynamin-related proteins (DRPs). Animal Opa1 (optical atrophy 1) and fungal Mgm1 (mitochondrial genome maintenance 1) are tacitly considered orthologs because their similar mitochondria-shaping roles are mediated by seemingly shared biochemical properties, and due to their presence in the two major opisthokontan subdivisions, Holozoa and Holomycota, respectively. However, molecular phylogenetics challenges this notion, suggesting that Opa1 and Mgm1 likely had separate, albeit convergent, evolutionary paths. Herein, we illuminate disparities in proteolytic processing, structure, and interaction network that may have bestowed on Opa1 and Mgm1 distinct mechanisms of membrane remodelling. A key disparity is that, unlike Mgm1, Opa1 directly recruits the mitochondrial phospholipid cardiolipin to remodel membranes. The differences outlined herein between the two DRPs could have broader impacts on mitochondrial morphogenesis. Outer and inner membrane fusion are autonomous in animals, which may have freed Opa1 to repurpose its intrinsic activity to remodel cristae, thereby regulating the formation of respiratory chain supercomplexes. More significantly, Opa1-mediated crista remodelling has emerged as an integral part of cytochrome c-regulated apoptosis in vertebrates, and perhaps in the cenancestor of animals. By contrast, outer and inner membrane fusion are coupled in budding yeast. Consequently, Mgm1 membrane-fusion activity is inextricable from its role in the biogenesis of fungal lamellar cristae. These disparate mitochondrial DRPs ultimately may have contributed to the different modes of multicellularity that have evolved within Opisthokonta.

A new member of the dynamin superfamily modulates mitochondrial membrane branching in Trypanosoma brucei

Unlike most other eukaryotes, where mitochondria continuously fuse and divide, the mitochondrion of trypanosome cells forms a single and continuously interconnected network that divides only during cytokinesis. However, the machinery governing mitochondrial remodeling and interconnection of trypanosome mitochondrion remain largely unknown. We functionally characterize a new member of the dynamin superfamily protein (DSP) from T. brucei (TbMfnL), which shares similarity with a family of homologs present in various eukaryotic and prokaryotic phyla but not in opisthokonts like mammals and budding yeast. The sequence and domain organization of TbMfnL is distinct, and it is phylogenetically very distant from the yeast and mammalian dynamin-related proteins involved in mitochondrial fusion/fission dynamics, such as optic atrophy 1 (Opa1) and mitofusin (Mfn). TbMfnL localizes to the inner mitochondrial membrane facing the matrix and, upon overexpression, induces a strong increase in the interconnection and branching of mitochondrial filaments in a GTPase-dependent manner. TbMfnL is a component of a novel membrane remodeling machinery with an unprecedented matrix-side localization that is able to modulate the degree of inter-mitochondrial connections.

Evolution of ubiquitin, cytoskeleton, and vesicular trafficking machinery in giant viruses

Members of the phylum Nucleocytoviricota, which include "giant viruses" known for their large physical dimensions and genome lengths, are a diverse group of dsDNA viruses that infect a wide range of eukaryotic hosts. The genomes of nucleocytoviruses frequently encode eukaryotic signature proteins (ESPs) such as RNA- and DNA-processing proteins, vesicular trafficking factors, cytoskeletal components, and proteins involved in ubiquitin signaling. Despite the prevalence of these genes in many nucleocytoviruses, the timing and number of gene acquisitions remains unclear. While the presence of DNA- and RNA-processing proteins in nucleocytoviruses likely reflects ancient gene transfers, the origins and evolutionary history of other proteins are largely unknown. In this study, we examined the distribution and evolutionary history of a subset of viral-encoded ESPs (vESPs) that are widespread in nucleocytoviruses. Our results demonstrate that most vESPs involved in vesicular trafficking were acquired multiple times independently by nucleocytoviruses at different time points after the emergence of the eukaryotic supergroups, while viral proteins associated with cytoskeletal and ubiquitin system proteins exhibited a more complex evolutionary pattern exhibited by both shallow and deep branching viral clades. This pattern reveals a dynamic interplay between the co-evoluton of eukaryotes and their viruses, suggesting that the viral acquisition of many genes involved in cellular processes has occurred both through ancient and more recent horizontal gene transfers. The timing and frequency of these gene acquisitions may provide insight into their role and functional significance during viral infection.IMPORTANCEThis research is pertinent for understanding the evolution of nucleocytoviruses and their interactions with eukaryotic hosts. By investigating the distribution and evolutionary history of viral-encoded eukaryotic signature proteins, the study reveals gene transfer patterns, highlighting how viruses acquire genes that allow them to manipulate host cellular processes. Identifying the timing and frequency of gene acquisitions related to essential cellular functions provides insights into their roles during viral infections. This work expands our understanding of viral diversity and adaptability, contributing valuable knowledge to virology and evolutionary biology, while offering new perspectives on the relationship between viruses and their hosts.

Molecular mechanisms of mitochondrial dynamics

Mitochondria not only synthesize energy required for cellular functions but are also involved in numerous cellular pathways including apoptosis, calcium homoeostasis, inflammation and immunity. Mitochondria are dynamic organelles that undergo cycles of fission and fusion, and these transitions between fragmented and hyperfused networks ensure mitochondrial function, enabling adaptations to metabolic changes or cellular stress. Defects in mitochondrial morphology have been associated with numerous diseases, highlighting the importance of elucidating the molecular mechanisms regulating mitochondrial morphology. Here, we discuss recent structural insights into the assembly and mechanism of action of the core mitochondrial dynamics proteins, such as the dynamin-related protein 1 (DRP1) that controls division, and the mitofusins (MFN1 and MFN2) and optic atrophy 1 (OPA1) driving membrane fusion. Furthermore, we provide an updated view of the complex interplay between different proteins, lipids and organelles during the processes of mitochondrial membrane fusion and fission. Overall, we aim to present a valuable framework reflecting current perspectives on how mitochondrial membrane remodelling is regulated.

Antiviral Mx proteins have an ancient origin and widespread distribution among eukaryotes

Mx proteins, first identified in mammals, encode potent antiviral activity against a wide range of viruses. Mx proteins arose within the Dynamin superfamily of proteins (DSP), which mediate critical cellular processes, such as endocytosis and mitochondrial, plastid, and peroxisomal dynamics. Despite their crucial role, the evolutionary origins of Mx proteins are poorly understood. Through comprehensive phylogenomic analyses with progressively expanded taxonomic sampling, we demonstrate that Mx proteins predate the interferon signaling system in vertebrates. Our analyses find an ancient monophyletic DSP lineage in eukaryotes that groups vertebrate and invertebrate Mx proteins with fungal MxF proteins, the largely uncharacterized plant and algal Dynamin 4A/4C proteins, and representatives from several other eukaryotic lineages, suggesting that Mx-like proteins date back close to the origin of Eukarya. Our phylogenetic analyses also find host-encoded and nucleocytoplasmic large DNA viruses-encoded DSPs interspersed in four distinct DSP lineages, indicating recurrent viral theft of host DSPs. Our analyses thus reveal an ancient history of viral and antiviral functions encoded by the Dynamin superfamily in eukaryotes.

SUMOylation modulates mitochondrial dynamics in an in vitro rotenone model of Parkinson's disease

SUMOylation is a post-translational modification essential for various biological processes. SUMO proteins bind to target substrates in a three-step enzymatic pathway, which is rapidly reversible by the action of specific proteases, known as SENPs. Studies have shown that SUMOylation is dysregulated in several human disorders, including neurodegenerative diseases that are characterized by the progressive loss of neurons, mitochondrial dysfunction, deficits in autophagy, and oxidative stress. Considering the potential neuroprotective roles of SUMOylation, the aim of this study was to investigate the effects of SENP3 knockdown in H4 neuroglioma cells exposed to rotenone, an in vitro model of cytotoxicity that mimics dopaminergic loss in Parkinson's disease (PD). The current data show that SENP3 knockdown increases SUMO-2/3 conjugates, which is accompanied by reduced levels of the mitochondrial fission protein Drp1 and increased levels of the mitochondrial fusion protein OPA1. Of high interest, SENP3 knockdown prevented rotenone-induced superoxide production and cellular death. Taken together, these findings highlight the importance of SUMOylation in maintaining mitochondrial homeostasis and the neuroprotective potential of this modification in PD.

Lumpy skin disease virus enters into host cells via dynamin-mediated endocytosis and macropinocytosis

Lumpy skin disease virus (LSDV), a ruminant poxvirus of the Capripoxvirus genus, is the etiologic agent of an economically important cattle disease categorized as a notifiable disease by the World Organization for Animal Health. However, the endocytic pathway and their regulatory molecules have not been characterized for LSDV. In the present study, specific pharmacological inhibitors were used to analyze the mechanism of LSDV entry into Mardin-Darby Bovine Kidney cell (MDBK) and bovine mammary epithelial cell (BMEC). The results showed that LSDV entered MDBK and BMEC cells depends on low-pH conditions and dynamin. However, the inhibitor of caveolae- and clathrin-mediated endocytosis cann't inhibit LSDV entry into MDBK and BMEC cells. Furthermore, treatment with specific inhibitors demonstrated that LSDV entry into MDBK and BMEC cells via macropinocytosis depended on the Na1/H1 exchanger (NHE) but not phosphatidylinositol 3-kinase (PI3K). In addition, results demonstrated that these inhibitors inhibited LSDV entry but did not have effect on LSDV binding. Taken together, our study demonstrated that LSDV enters MDBK and BMEC cells through macropinocytosis pathway in a low-PH- and dynamin-dependent manner while independent on PI3K. Results presented in this study potentially provides insight into the entry mechanisms of LSDV, and it may facilitate the development of therapeutic interventions.

The Large GTPase Guanylate-Binding Protein-1 (GBP-1) Promotes Mitochondrial Fission in Glioblastoma

Glioblastomas (aka Glioblastoma multiformes (GBMs)) are the most deadly of the adult brain tumors. Even with aggressive treatment, the prognosis is extremely poor. The large GTPase Guanylate-Binding Protein-1 (GBP-1) contributes to the poor prognosis of GBM by promoting migration and invasion. GBP-1 is substantially localized to the cytosolic side of the outer membrane of mitochondria in GBM cells. Because mitochondrial dynamics, particularly mitochondrial fission, can drive cell migration and invasion, the potential interactions between GBP-1 and mitochondrial dynamin-related protein 1 (Drp1) were explored. Drp1 is the major driver of mitochondrial fission. While GBP-1 and Drp1 both had punctate distributions within the cytoplasm and localized to regions of the cytoplasmic side of the plasma membrane of GBM cells, the proteins were only molecularly co-localized at the mitochondria. Subcellular fractionation showed that the presence of elevated GBP-1 promoted the movement of Drp1 from the cytosol to the mitochondria. The migration of U251 cells treated with the Drp1 inhibitor, Mdivi-1, was less inhibited in the cells with elevated GBP-1. Elevated GBP-1 in GBM cells resulted in shorter and wider mitochondria, most likely from mitochondrial fission. Mitochondrial fission can drive several important cellular processes, including cell migration, invasion, and metastasis.

MX2 forms nucleoporin-comprising cytoplasmic biomolecular condensates that lure viral capsids

Human myxovirus resistance 2 (MX2) can restrict HIV-1 and herpesviruses at a post-entry step through a process requiring an interaction between MX2 and the viral capsids. The involvement of other host cell factors, however, remains poorly understood. Here, we mapped the proximity interactome of MX2, revealing strong enrichment of phenylalanine-glycine (FG)-rich proteins related to the nuclear pore complex as well as proteins that are part of cytoplasmic ribonucleoprotein granules. MX2 interacted with these proteins to form multiprotein cytoplasmic biomolecular condensates that were essential for its anti-HIV-1 and anti-herpes simplex virus 1 (HSV-1) activity. MX2 condensate formation required the disordered N-terminal region and MX2 dimerization. Incoming HIV-1 and HSV-1 capsids associated with MX2 at these dynamic cytoplasmic biomolecular condensates, preventing nuclear entry of their viral genomes. Thus, MX2 forms cytoplasmic condensates that likely act as nuclear pore decoys, trapping capsids and inducing premature viral genome release to interfere with nuclear targeting of HIV-1 and HSV-1.

Characterization of Myxovirus resistance (Mx) gene from Chinese seabass Lateolabrax maculatus: Insights into the evolution and function of Mx genes

Chinese seabass (Lateolabrax maculatus) stands out as one of the most sought-after and economically significant species in aquaculture within China. Diseases of L. maculatus occur frequently due to the degradation of the germplasm, the aggravation of environmental pollution of water, and the reproduction of pathogenic microorganisms, inflicting considerable economic losses on the Chinese seabass industry. The Myxovirus resistance (Mx) gene plays pivotal roles in the antiviral immune response ranging from mammals to fish. However, the function of the Mx gene in L. maculatus is still unknown. Firstly, the origin and evolutionary history of Mx proteins was elucidated in this study. Subsequently, an Mx gene from L. maculatus (designed as LmMxA gene) was identified, and its functions in combating antiviral and antibacterial threats were investigated. Remarkably, our findings suggested that while Mx group genes were present in chordates, DYN group genes were present in everything from single-celled animals to humans. Furthermore, our investigation revealed that the LmMxA mRNA level increased in the kidney, spleen and liver subsequent to Vibrio anguillarum and poly(I:C) challenged. Immunofluorescence analysis indicated that LmMxA is predominantly localization in the nucleus and the cytoplasm. Notably, the expression of MAVS, IFN1 and Mx1 increased when LmMxA was overexpression within the EPC cells. Moreover, through assessment via cytopathic effect (CPE), virus titer, and antibacterial activity, it becomes evident that LmMxA exerts a dual role in bolstering both antiviral and antibacterial immune responses. These compelling findings laid the foundation for further exploring the mechanism of LmMxA in response to innate immunity of L. maculatus.

Antiviral Mx proteins have an ancient origin and widespread distribution among eukaryotes

First identified in mammals, Mx proteins are potent antivirals against a broad swathe of viruses. Mx proteins arose within the Dynamin superfamily of proteins (DSP), mediating critical cellular processes, such as endocytosis and mitochondrial, plastid, and peroxisomal dynamics. And yet, the evolutionary origins of Mx proteins are poorly understood. Using a series of phylogenomic analyses with stepwise increments in taxonomic coverage, we show that Mx proteins predate the interferon signaling system in vertebrates. Our analyses find an ancient monophyletic DSP lineage in eukaryotes that groups vertebrate and invertebrate Mx proteins with previously undescribed fungal MxF proteins, the relatively uncharacterized plant and algal Dynamin 4A/4C proteins, and representatives from several early-branching eukaryotic lineages. Thus, Mx-like proteins date back close to the origin of Eukarya. Our phylogenetic analyses also reveal that host-encoded and NCLDV (nucleocytoplasmic large DNA viruses)-encoded DSPs are interspersed in four distinct DSP lineages, indicating recurrent viral theft of host DSPs. Our analyses thus reveal an ancient history of viral and antiviral functions encoded by the Dynamin superfamily in eukaryotes.

Structural and Evolutionary Aspects of Plant Endocytosis

Endocytosis is an essential eukaryotic process that maintains the homeostasis of the plasma membrane proteome by vesicle-mediated internalization. Its predominant mode of operation utilizes the polymerization of the scaffold protein clathrin forming a coat around the vesicle; therefore, it is termed clathrin-mediated endocytosis (CME). Throughout evolution, the machinery that mediates CME is marked by losses, multiplications, and innovations. CME employs a limited number of conserved structural domains and folds, whose assembly and connections are species dependent. In plants, many of the domains are grouped into an ancient multimeric complex, the TPLATE complex, which occupies a central position as an interaction hub for the endocytic machinery. In this review, we provide an overview of the current knowledge regarding the structural aspects of plant CME, and we draw comparisons to other model systems. To do so, we have taken advantage of recent developments with respect to artificial intelligence-based protein structure prediction.

Mesoscopic elasticity controls dynamin-driven fission of lipid tubules

Mesoscale physics bridges the gap between the microscopic degrees of freedom of a system and its large-scale continuous behavior and highlights the role of a few key quantities in complex and multiscale phenomena, like dynamin-driven fission of lipid membranes. The dynamin protein wraps the neck formed during clathrin-mediated endocytosis, for instance, and constricts it until severing occurs. Although ubiquitous and fundamental for life, the cooperation between the GTP-consuming conformational changes within the protein and the full-scale response of the underlying lipid substrate is yet to be unraveled. In this work, we build an effective mesoscopic model from constriction to fission of lipid tubules based on continuum membrane elasticity and implicitly accounting for ratchet-like power strokes of dynamins. Localization of the fission event, the overall geometry, and the energy expenditure we predict comply with the major experimental findings. This bolsters the idea that a continuous picture emerges soon enough to relate dynamin polymerization length and membrane rigidity and tension with the optimal pathway to fission. We therefore suggest that dynamins found in in vivo processes may optimize their structure accordingly. Ultimately, we shed light on real-time conductance measurements available in literature and predict the fission time dependency on elastic parameters.

Drp1: Focus on Diseases Triggered by the Mitochondrial Pathway

Drp1 (Dynamin-Related Protein 1) is a cytoplasmic GTPase protein encoded by the DNM1L gene that influences mitochondrial dynamics by mediating mitochondrial fission processes. Drp1 has been demonstrated to play an important role in a variety of life activities such as cell survival, proliferation, migration, and death. Drp1 has been shown to play different physiological roles under different physiological conditions, such as normal and inflammation. Recently studies have revealed that Drp1 plays a critical role in the occurrence, development, and aggravation of a series of diseases, thereby it serves as a potential therapeutic target for them. In this paper, we review the structure and biological properties of Drp1, summarize the biological processes that occur in the inflammatory response to Drp1, discuss its role in various cancers triggered by the mitochondrial pathway and investigate effective methods for targeting Drp1 in cancer treatment. We also synthesized the phenomena of Drp1 involving in the triggering of other diseases. The results discussed herein contribute to our deeper understanding of mitochondrial kinetic pathway-induced diseases and their therapeutic applications. It is critical for advancing the understanding of the mechanisms of Drp1-induced mitochondrial diseases and preventive therapies.

Cell entry of bovine respiratory syncytial virus through clathrin-mediated endocytosis is regulated by PI3K-Akt and Src-JNK pathways

Bovine respiratory syncytial virus (BRSV) is an RNA virus with envelope that causes acute, febrile, and highly infectious respiratory diseases in cattle. However, the manner and mechanism of BRSV entry into cells remain unclear. In this study, we aimed to explore the entry manner of BRSV into MDBK cells and its regulatory mechanism. Our findings, based on virus titer, virus copies, western blot and IFA analysis, indicate that BRSV enters MDBK cells through endocytosis, relying on dynamin, specifically via clathrin-mediated endocytosis rather than caveolin-mediated endocytosis and micropinocytosis. We observed that the entered BRSV initially localizes in early endosomes and subsequently localizes in late endosomes. Additionally, our results of western blot, virus titer and virus copies demonstrate that BRSV entry through clathrin-mediated endocytosis is regulated by PI3K-Akt and Src-JNK signaling pathways. Overall, our study suggests that BRSV enters MDBK cells through clathrin-mediated endocytosis, entered BRSV is trafficked to late endosome via early endosome, BRSV entry through clathrin-mediated endocytosis is regulated by PI3K-Akt and Src-JNK signaling pathways.

Balbiani body of basal insects is potentially involved in multiplication and selective elimination of mitochondria

Oocytes of both vertebrates and invertebrates often contain an intricate organelle assemblage, termed the Balbiani body (Bb). It has previously been suggested that this assemblage is involved in the delivery of organelles and macromolecules to the germ plasm, formation of oocyte reserve materials, and transfer of mitochondria to the next generation. To gain further insight into the function of the Bb, we performed a series of analyses and experiments, including computer-aided 3-dimensional reconstructions, detection of DNA (mtDNA) synthesis as well as immunolocalization studies. We showed that in orthopteran Meconema meridionale, the Bb comprises a network of mitochondria and perinuclear nuage aggregations. As oogenesis progresses, the network expands filling almost entire ooplasm, then partitions into several smaller entities, termed micro-networks, and ultimately into individual mitochondria. As in somatic cells, this process involves microfilaments and elements of endoplasmic reticulum. We showed also that at least some of the individual mitochondria are surrounded by phagophores and eliminated via mitophagy. These findings support the idea that the Bb is implicated in the multiplication and selective elimination of (defective) mitochondria and therefore may participate in the transfer of undamaged (healthy) mitochondria to the next generation.

Membrane fusion and fission during eukaryogenesis

All eukaryotes can be traced back to a single shared ancestral lineage that emerged from interactions between different prokaryotic cells. Current models of eukaryogenesis describe various selective forces and evolutionary mechanisms that contributed to the formation of eukaryotic cells. Central to this process were significant changes in cellular structure, resulting in the configuration of a new cell type characterized by internal membrane compartments. Additionally, eukaryogenesis results in a life cycle that relies on cell-cell fusion. We discuss the potential roles of proteins involved in remodeling cellular membranes, highlighting two critical stages in the evolution of eukaryotes: the internalization of symbiotic partners and a scenario wherein the emergence of sexual reproduction is linked to a polyploid ancestor generated by cell-cell fusion.

Advancements in the study of synaptic plasticity and mitochondrial autophagy relationship

Synapses serve as the points of communication between neurons, consisting primarily of three components: the presynaptic membrane, synaptic cleft, and postsynaptic membrane. They transmit signals through the release and reception of neurotransmitters. Synaptic plasticity, the ability of synapses to undergo structural and functional changes, is influenced by proteins such as growth-associated proteins, synaptic vesicle proteins, postsynaptic density proteins, and neurotrophic growth factors. Furthermore, maintaining synaptic plasticity consumes more than half of the brain's energy, with a significant portion of this energy originating from ATP generated through mitochondrial energy metabolism. Consequently, the quantity, distribution, transport, and function of mitochondria impact the stability of brain energy metabolism, thereby participating in the regulation of fundamental processes in synaptic plasticity, including neuronal differentiation, neurite outgrowth, synapse formation, and neurotransmitter release. This article provides a comprehensive overview of the proteins associated with presynaptic plasticity, postsynaptic plasticity, and common factors between the two, as well as the relationship between mitochondrial energy metabolism and synaptic plasticity.

Allosteric control of dynamin-related protein 1 through a disordered C-terminal Short Linear Motif

The mechanochemical GTPase dynamin-related protein 1 (Drp1) catalyzes mitochondrial and peroxisomal fission, but the regulatory mechanisms remain ambiguous. Here we find that a conserved, intrinsically disordered, six-residue Short Linear Motif at the extreme Drp1 C-terminus, named CT-SLiM, constitutes a critical allosteric site that controls Drp1 structure and function in vitro and in vivo. Extension of the CT-SLiM by non-native residues, or its interaction with the protein partner GIPC-1, constrains Drp1 subunit conformational dynamics, alters self-assembly properties, and limits cooperative GTP hydrolysis, surprisingly leading to the fission of model membranes in vitro. In vivo, the involvement of the native CT-SLiM is critical for productive mitochondrial and peroxisomal fission, as both deletion and non-native extension of the CT-SLiM severely impair their progression. Thus, contrary to prevailing models, Drp1-catalyzed membrane fission relies on allosteric communication mediated by the CT-SLiM, deceleration of GTPase activity, and coupled changes in subunit architecture and assembly-disassembly dynamics.

Insights into the role of the conserved GTPase domain residues T62 and S277 in yeast Dnm1

Mitochondrial division is a highly regulated process. The master regulator of this process is the multi-domain, conserved protein called Dnm1 in yeast. In this study, we systematically analyzed two residues, T62 and S277, reported to be putatively phosphorylated in the GTPase domain of the protein. These residues lie in the G2 and G5 motifs of the GTPase domain. Both residues are important for the function of the protein, as evident from in vivo and in vitro analysis of the non-phosphorylatable and phosphomimetic variants. Dnm1T62A/D and Dnm1S277A/D showed differences with respect to the protein localization and puncta dynamics in vivo, albeit both were non-functional as assessed by mitochondrial morphology and GTPase activity. Overall, the secondary structure of the protein variants was unaltered, but local conformational changes were observed. Interestingly, both Dnm1T62A/D and Dnm1S277A/D exhibited dominant-negative behavior when expressed in cells containing endogenous Dnm1. To our knowledge, we report for the first time a single residue (S277) change that does not alter the localization of Dnm1 but makes it non-functional in a dominant-negative manner. Intriguingly, the two residues analyzed in this study are present in the same domain but exhibit variable effects when mutated to alanine or aspartic acid.

The Chemical Inhibitors of Endocytosis: From Mechanisms to Potential Clinical Applications

Endocytosis is one of the major ways cells communicate with their environment. This process is frequently hijacked by pathogens. Endocytosis also participates in the oncogenic transformation. Here, we review the approaches to inhibit endocytosis, discuss chemical inhibitors of this process, and discuss potential clinical applications of the endocytosis inhibitors.

Clomipramine inhibits dynamin GTPase activity by L-α-phosphatidyl-L-serine stimulation

Three dynamin isoforms play critical roles in clathrin-dependent endocytosis. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters host cells via clathrin-dependent endocytosis. We previously reported that 3-(3-chloro-10,11-dihydro-5H-dibenzo[b,f]azepin-5-yl)-N,N-dimethylpropan-1-amine (clomipramine) inhibits the GTPase activity of dynamin 1, which is in mainly neuron. Therefore, we investigated whether clomipramine inhibits the activity of other dynamin isoforms in this study. We found that, similar to its inhibitory effect on dynamin 1, clomipramine inhibited the l-α-phosphatidyl-l-serine-stimulated GTPase activity of dynamin 2, which is expressed ubiquitously, and dynamin 3, which is expressed in the lung. Inhibition of GTPase activity raises the possibility that clomipramine can suppress SARS-CoV-2 entry into host cells.

SynDLP is a dynamin-like protein of Synechocystis sp. PCC 6803 with eukaryotic features

Dynamin-like proteins are membrane remodeling GTPases with well-understood functions in eukaryotic cells. However, bacterial dynamin-like proteins are still poorly investigated. SynDLP, the dynamin-like protein of the cyanobacterium Synechocystis sp. PCC 6803, forms ordered oligomers in solution. The 3.7 Å resolution cryo-EM structure of SynDLP oligomers reveals the presence of oligomeric stalk interfaces typical for eukaryotic dynamin-like proteins. The bundle signaling element domain shows distinct features, such as an intramolecular disulfide bridge that affects the GTPase activity, or an expanded intermolecular interface with the GTPase domain. In addition to typical GD-GD contacts, such atypical GTPase domain interfaces might be a GTPase activity regulating tool in oligomerized SynDLP. Furthermore, we show that SynDLP interacts with and intercalates into membranes containing negatively charged thylakoid membrane lipids independent of nucleotides. The structural characteristics of SynDLP oligomers suggest it to be the closest known bacterial ancestor of eukaryotic dynamin.

Zebrafish dnm1a gene plays a role in the formation of axons and synapses in the nervous tissue

Classical dynamins (DNMs) are GTPase proteins engaged in endocytosis, a fundamental process for cargo internalization from the plasma membrane. In mammals, three DNM genes are present with different expression patterns. DNM1 is expressed at high levels in neurons, where it takes place in the recycling of synaptic vesicles; DNM2 is ubiquitously expressed, while DNM3 is found in the brain and in the testis. Due to the conservation of genes in comparison to mammals, we took advantage of a zebrafish model for functional characterization of dnm1a, ortholog of mammalian DNM1. Our data strongly demonstrated that dnm1a has a nervous tissue-specific expression pattern and plays a role in the formation of both axon and synapse. This is the first in vivo study that collects evidence about the effects of dnm1a loss of function in zebrafish, thus providing a new excellent model to be used in different scientific fields.

Phage defense origin of animal immunity

The innate immune system is the first line of defense against microbial pathogens. Many of the features of eukaryotic innate immunity have long been viewed as lineage-specific innovations, evolved to deal with the challenges and peculiarities of multicellular life. However, it has become increasingly apparent that in addition to evolving their own unique antiviral immune strategies, all lifeforms have some shared defense strategies in common. Indeed, critical fixtures of animal innate immunity bear striking resemblance in both structure and function to the multitude of diverse bacteriophage (phage) defense pathways discovered hidden in plain sight within the genomes of bacteria and archaea. This review will highlight many surprising examples of the recently revealed connections between prokaryotic and eukaryotic antiviral immune systems.

The Drp1-Mediated Mitochondrial Fission Protein Interactome as an Emerging Core Player in Mitochondrial Dynamics and Cardiovascular Disease Therapy

Mitochondria, the membrane-bound cell organelles that supply most of the energy needed for cell function, are highly regulated, dynamic organelles bearing the ability to alter both form and functionality rapidly to maintain normal physiological events and challenge stress to the cell. This amazingly vibrant movement and distribution of mitochondria within cells is controlled by the highly coordinated interplay between mitochondrial dynamic processes and fission and fusion events, as well as mitochondrial quality-control processes, mainly mitochondrial autophagy (also known as mitophagy). Fusion connects and unites neighboring depolarized mitochondria to derive a healthy and distinct mitochondrion. In contrast, fission segregates damaged mitochondria from intact and healthy counterparts and is followed by selective clearance of the damaged mitochondria via mitochondrial specific autophagy, i.e., mitophagy. Hence, the mitochondrial processes encompass all coordinated events of fusion, fission, mitophagy, and biogenesis for sustaining mitochondrial homeostasis. Accumulated evidence strongly suggests that mitochondrial impairment has already emerged as a core player in the pathogenesis, progression, and development of various human diseases, including cardiovascular ailments, the leading causes of death globally, which take an estimated 17.9 million lives each year. The crucial factor governing the fission process is the recruitment of dynamin-related protein 1 (Drp1), a GTPase that regulates mitochondrial fission, from the cytosol to the outer mitochondrial membrane in a guanosine triphosphate (GTP)-dependent manner, where it is oligomerized and self-assembles into spiral structures. In this review, we first aim to describe the structural elements, functionality, and regulatory mechanisms of the key mitochondrial fission protein, Drp1, and other mitochondrial fission adaptor proteins, including mitochondrial fission 1 (Fis1), mitochondrial fission factor (Mff), mitochondrial dynamics 49 (Mid49), and mitochondrial dynamics 51 (Mid51). The core area of the review focuses on the recent advances in understanding the role of the Drp1-mediated mitochondrial fission adaptor protein interactome to unravel the missing links of mitochondrial fission events. Lastly, we discuss the promising mitochondria-targeted therapeutic approaches that involve fission, as well as current evidence on Drp1-mediated fission protein interactions and their critical roles in the pathogeneses of cardiovascular diseases (CVDs).

Cyanobacterial membrane dynamics in the light of eukaryotic principles

Intracellular compartmentalization is a hallmark of eukaryotic cells. Dynamic membrane remodeling, involving membrane fission/fusion events, clearly is crucial for cell viability and function, as well as membrane stabilization and/or repair, e.g., during or after injury. In recent decades, several proteins involved in membrane stabilization and/or dynamic membrane remodeling have been identified and described in eukaryotes. Yet, while typically not having a cellular organization as complex as eukaryotes, also bacteria can contain extra internal membrane systems besides the cytoplasmic membranes (CMs). Thus, also in bacteria mechanisms must have evolved to stabilize membranes and/or trigger dynamic membrane remodeling processes. In fact, in recent years proteins, which were initially defined being eukaryotic inventions, have been recognized also in bacteria, and likely these proteins shape membranes also in these organisms. One example of a complex prokaryotic inner membrane system is the thylakoid membrane (TM) of cyanobacteria, which contains the complexes of the photosynthesis light reaction. Cyanobacteria are evolutionary closely related to chloroplasts, and extensive remodeling of the internal membrane systems has been observed in chloroplasts and cyanobacteria during membrane biogenesis and/or at changing light conditions. We here discuss common principles guiding eukaryotic and prokaryotic membrane dynamics and the proteins involved, with a special focus on the dynamics of the cyanobacterial TMs and CMs.

Na, K-ATPase α1 cooperates with its endogenous ligand to reprogram immune microenvironment of lung carcinoma and promotes immune escape

Dysregulated endocrine hormones (EHs) contribute to tumorigenesis, but how EHs affect the tumor immune microenvironment (TIM) and the immunotherapy of non-small cell lung cancer (NSCLC) is still unclear. Here, endogenous ouabain (EO), an adrenergic hormone, is elevated in patients with NSCLC and closely related to tumor pathological stage, metastasis, and survival. EO promotes the suppression of TIM in vivo by modulating the expression of immune checkpoint proteins, in which programmed cell death protein ligand 1 (PD-L1) plays a major role. EO increases PD-L1 transcription; however, the EO receptor Na- and K-dependent adenosine triphosphatase (Na, K-ATPase) α1 interacts with PD-L1 to trigger the endocytic degradation of PD-L1. This seemingly contradictory result led us to discover the mechanism whereby EO cooperates with Na, K-ATPase α1 to finely control PD-L1 expression and dampen tumoral immunity. In conclusion, the Na, K-ATPase α1/EO signaling facilitates immune escape in lung cancer, and manipulation of this signaling shows great promise in improving immunotherapy for lung adenocarcinoma.

Wiskostatin and other carbazole scaffolds as off target inhibitors of dynamin I GTPase activity and endocytosis

Wiskostatin (1-(3,6-dibromo-9H-carbazol-9-yl)-3-(dimethylamino)propan-2-ol) (1) is a carbazole-based compound reported as a specific and relatively potent inhibitor of the N-WASP actin remodelling complex (S-isomer EC₅₀ = 4.35 μM; R-isomer EC₅₀ = 3.44 μM). An NMR solution structure showed that wiskostatin interacts with a cleft in the regulatory GTPase binding domain of N-WASP. However, numerous studies have reported wiskostatin's actions on membrane transport and cytokinesis that are independent of the N-WASP-Arp2/3 complex pathway, but offer limited alternative explanation. The large GTPase, dynamin has established functional roles in these pathways. This study reveals that wiskostatin and its analogues, as well as other carbazole-based compounds, are inhibitors of helical dynamin GTPase activity and endocytosis. We characterise the effects of wiskostatin on in vitro dynamin GTPase activity, in-cell endocytosis, and determine the importance of wiskostatin functional groups on these activities through design and synthesis of libraries of wiskostatin analogues. We also examine whether other carbazole-based scaffolds frequently used in research or the clinic also modulate dynamin and endocytosis. Understanding off-targets for compounds used as research tools is important to be able to confidently interpret their action on biological systems, particularly when the target and off-targets affect overlapping mechanisms (e.g. cytokinesis and endocytosis). Herein we demonstrate that wiskostatin is a dynamin inhibitor (IC₅₀ 20.7 ± 1.2 μM) and a potent inhibitor of clathrin mediated endocytosis (IC₅₀ = 6.9 ± 0.3 μM). Synthesis of wiskostatin analogues gave rise to 1-(9H-carbazol-9-yl)-3-((4-methylbenzyl)amino)propan-2-ol (35) and 1-(9H-carbazol-9-yl)-3-((4-chlorobenzyl)amino)propan-2-ol (43) as potent dynamin inhibitors (IC₅₀ = 1.0 ± 0.2 μM), and (S)-1-(3,6-dibromo-9H-carbazol-9-yl)-3-(dimethylamino)propan-2-ol (8a) and (R)-1-(3,6-dibromo-9H-carbazol-9-yl)-3-(dimethylamino)propan-2-ol (8b) that are amongst the most potent inhibitors of clathrin mediated endocytosis yet reported (IC₅₀ = 2.3 ± 3.3 and 2.1 ± 1.7 μM, respectively).

An evolutionarily conserved N-terminal leucine is essential for MX1 GTPase antiviral activity against different families of RNA viruses

Myxovirus resistance protein 1 (MX1) and MX2 are homologous, dynamin-like large GTPases, induced upon interferon exposure. Human MX1 (HsMX1) is known to inhibit many viruses, including influenza A virus, by likely acting at various steps of their life cycles. Despite decades of studies, the mechanism(s) of action with which MX1 proteins manage to inhibit target viruses is not fully understood. MX1 proteins are mechano-enzymes and share a similar organization to dynamin, with a GTPase domain and a carboxy-terminal stalk domain, connected by a bundle signaling element. These three elements are known to be essential for antiviral activity. HsMX1 has two unstructured regions, the L4 loop, also essential for antiviral activity, and a short amino (N)-terminal region, which greatly varies between MX1 proteins of different species. The role of this N-terminal domain in antiviral activity is not known. Herein, using mutagenesis, imaging, and biochemical approaches, we demonstrate that the N-terminal domain of HsMX1 is essential for antiviral activity against influenza A virus, Vesicular Stomatitis Virus, and La Crosse virus. Furthermore, we pinpoint a highly conserved leucine within this region, which is absolutely crucial for human, mouse, and bat MX1 protein antiviral activity. Importantly, mutation of this leucine does not compromise GTPase activity or oligomerization capabilities but does modify MX1 protein subcellular localization. The discovery of this essential and highly conserved residue defines this region as key for antiviral activity and may reveal insights as to the mechanism(s) of action of MX1 proteins.

Prodrugs of the Archetypal Dynamin Inhibitor Bis-T-22

The Bis-T series of compounds comprise some of the most potent inhibitors of dynamin GTPase activity yet reported, e. g., (2E,2'E)-N,N'-(propane-1,3-diyl)bis(2-cyano-3-(3,4-dihydroxyphenyl)acrylamide) (2), Bis-T-22. The catechol moieties are believed to limit cell permeability, rendering these compounds largely inactive in cells. To solve this problem, a prodrug strategy was envisaged and eight ester analogues were synthesised. The shortest and bulkiest esters (acetate and butyl/tert-butyl) were found to be insoluble under physiological conditions, whilst the remaining five were soluble and stable under these conditions. These five were analysed for plasma stability and half-lives ranged from ∼2.3 min (propionic ester 4), increasing with size and bulk, to greater than 24 hr (dimethyl carbamate 10). Similar profiles where observed with the rate of formation of Bis-T-22 with half-lives ranging from ∼25 mins (propionic ester 4). Propionic ester 4 was chosen to undergo further testing and was found to inhibit endocytosis in a dose-dependent manner with IC50 ∼8 μM, suggesting this compound is able to effectively cross the cell membrane where it is rapidly hydrolysed to the desired Bis-T-22 parent compound.

Regulation of fenestra formation via actin-dynamin2 interaction in rat pituitary endothelial cells

Endothelial fenestrae are transcellular pores divided by a diaphragm consisting of plasmalemma vesicle-associated protein (PLVAP). They function as a channel for peptide hormones and other substances. Invagination of the plasma membrane is necessary for the fenestra formation. The actin cytoskeleton is essential for scission of endocytic vesicles from the invaginated plasma membrane. Therefore, we examined the involvement of the actin cytoskeleton in fenestra formation in cultured endothelial cells isolated from the anterior lobe (AL) of the rat pituitary, using immunofluorescence and scanning electron microscopy. Inhibition of polymerization and depolymerization of the actin cytoskeleton by latrunculin A and jasplakinolide, respectively, remarkably increased the PLVAP-positive sieve plate area and number of fenestrae. Jasplakinolide significantly affected the arrangement of the fenestra on the cell surface, resulting in parallel serpentine furrows of the fenestra. These results suggest that the actin cytoskeleton not only induces fenestra formation but also regulates cell arrangement. Dynamin is a scission protein of the invaginated plasma membrane and interacts with the actin cytoskeleton. We found that dynamin2 is mainly expressed in the endothelial cells of the rat AL. We then investigated the function of dynamin2 by the treatment with dyngo-4a, a potent inhibitor of dynamin1 and dynamin2, on the fenestra formation. As a result, the PLVAP-positive area is significantly increased by the treatment. These results show that the actin-dynamin2 interaction is essential for the control of the fenestra formation in endothelial cells of rat AL. In conclusion, the actin cytoskeleton and dynamin2 function as regulators of endothelial fenestra formation.

A dominant negative mitofusin causes mitochondrial perinuclear clusters because of aberrant tethering

In vertebrates, mitochondrial outer membrane fusion is mediated by two mitofusin paralogs, Mfn1 and Mfn2, conserved dynamin superfamily proteins. Here, we characterize a variant of mitofusin reported in patients with CMT2A where a serine is replaced with a proline (Mfn2-S350P and the equivalent in Mfn1, S329P). This serine is in a hinge domain (Hinge 2) that connects the globular GTPase domain to the adjacent extended helical bundle. We find that expression of this variant results in prolific and stable mitochondrial tethering that also blocks mitochondrial fusion by endogenous wild-type mitofusin. The formation of mitochondrial perinuclear clusters by this CMT2A variant requires normal GTPase domain function and formation of a mitofusin complex across two membranes. We propose that conformational dynamics mediated by Hinge 2 and regulated by GTP hydrolysis are disrupted by the substitution of proline at S329/S350 and this prevents progression from tethering to membrane fusion. Thus, our data are consistent with a model for mitofusin-mediated membrane fusion where Hinge 2 supports a power stroke to progress from the tethering complex to membrane fusion.

Asymmetric inheritance of cytoophidia could contribute to determine cell fate and plasticity: The onset of alternative differentiation patterns in daughter cells may rely on the acquisition of either CTPS or IMPDH cytoophidia: The onset of alternative differentiation patterns in daughter cells may rely on the acquisition of either CTPS or IMPDH cytoophidia

Two enzymes involved in the synthesis of pyrimidine and purine nucleotides, CTP synthase (CTPS) and IMP dehydrogenase (IMPDH), can assemble into a single or very few large filaments called rods and rings (RR) or cytoophidia. Most recently, asymmetric cytoplasmic distribution of organelles during cell division has been described as a decisive event in hematopoietic stem cell fate. We propose that cytoophidia, which could be considered as membrane-less organelles, may also be distributed asymmetrically during mammalian cell division as previously described for Schizosaccharomyces pombe. Furthermore, because each type of nucleotide intervenes in distinct processes (e.g., membrane synthesis, glycosylation, and G protein-signaling), alterations in the rate of synthesis of specific nucleotide types could influence cell differentiation in multiple ways. Therefore, we hypothesize that whether a daughter cell inherits or not CTPS or IMPDH filaments determines its fate and that this asymmetric inheritance, together with the dynamic nature of these structures enables plasticity in a cell population.

Cancer as a biophysical disease: Targeting the mechanical-adaptability program

With the number of cancer cases projected to significantly increase over time, researchers are currently exploring "nontraditional" research fields in the pursuit of novel therapeutics. One emerging area that is steadily gathering interest revolves around cellular mechanical machinery. When looking broadly at the physical properties of cancer, it has been debated whether a cancer could be defined as either stiffer or softer across cancer types. With numerous articles supporting both sides, the evidence instead suggests that cancer is not particularly regimented. Instead, cancer is highly adaptable, allowing it to endure the constantly changing microenvironments cancer cells encounter, such as tumor compression and the shear forces in the vascular system and body. What allows cancer cells to achieve this adaptability are the particular proteins that make up the mechanical network, leading to a particular mechanical program of the cancer cell. Coincidentally, some of these proteins, such as myosin II, α-actinins, filamins, and actin, have either altered expression in cancer and/or some type of direct involvement in cancer progression. For this reason, targeting the mechanical system as a therapeutic strategy may lead to more efficacious treatments in the future. However, targeting the mechanical program is far from trivial. As involved as the mechanical program is in cancer development and metastasis, it also helps drive many other key cellular processes, such as cell division, cell adhesion, metabolism, and motility. Therefore, anti-cancer treatments targeting the mechanical program must take great care to avoid potential side effects. Here, we introduce the potential of targeting the mechanical program while also providing its challenges and shortcomings as a strategy for cancer treatment.

Drp1 and the cytoskeleton: mechanistic nexus in mitochondrial division

Dynamin-related protein 1 (Drp1), the master regulator of mitochondrial division (MD), interacts with the cytoskeletal elements, namely filamentous actin (F-actin), microtubules (MT), and septins that coincidentally converge at MD sites. However, the mechanistic contributions of these critical elements to, and their cooperativity in, MD remain poorly characterized. Emergent data indicate that the cytoskeleton plays combinatorial modulator, mediator, and effector roles in MD by 'priming' and 'channeling' Drp1 for mechanoenzymatic membrane remodeling. In this brief review, we will outline our current understanding of Drp1-cytoskeleton interactions, focusing on recent progress in the field and a plausible 'diffusion barrier' role for the cytoskeleton in MD.

Molecular Mechanism and Regulation of Autophagy and Its Potential Role in Epilepsy

Autophagy is an evolutionally conserved degradation mechanism for maintaining cell homeostasis whereby cytoplasmic components are wrapped in autophagosomes and subsequently delivered to lysosomes for degradation. This process requires the concerted actions of multiple autophagy-related proteins and accessory regulators. In neurons, autophagy is dynamically regulated in different compartments including soma, axons, and dendrites. It determines the turnover of selected materials in a spatiotemporal control manner, which facilitates the formation of specialized neuronal functions. It is not surprising, therefore, that dysfunctional autophagy occurs in epilepsy, mainly caused by an imbalance between excitation and inhibition in the brain. In recent years, much attention has been focused on how autophagy may cause the development of epilepsy. In this article, we overview the historical landmarks and distinct types of autophagy, recent progress in the core machinery and regulation of autophagy, and biological roles of autophagy in homeostatic maintenance of neuronal structures and functions, with a particular focus on synaptic plasticity. We also discuss the relevance of autophagy mechanisms to the pathophysiology of epileptogenesis.

Four Mx Genes Identified in Andrias davidianus and Characterization of Their Response to Chinese Giant Salamander Iridovirus Infection

Amphibians, including Andrias davidianus, are declining worldwide partly due to infectious diseases. The Myxovirus resistance (Mx) gene is a typical interferon (IFN)-stimulated gene (ISG) involved in the antiviral immunity. Therefore, knowledge regarding the antiviral immunity of A. davidianus can be used for improved reproduction in captivity and protection in the wild. In this study, we amplified and characterized four different A. davidianus Mx genes (adMx) and generated temporal mRNA expression profiles in healthy and Chinese giant salamander iridovirus (GSIV) infected A. davidianus by qualitative real-time PCR (qPCR). The four adMx genes ranged in length from 2008 to 2840 bp. The sequences revealed conserved protein domains including the dynamin superfamily signature motif and the tripartite guanosine-5-triphosphate (GTP)-binding motif. Gene and deduced amino acid sequence alignment revealed relatively high sequence identity with the Mx genes and proteins of other vertebrates. In phylogenetic analysis, the adMx genes clustered together, but also clustered closely with those of fish species. The four adMx genes were broadly expressed in healthy A. davidianus, but were differentially expressed in the spleen during the GSIV infection. Our results show that the adMx genes share major structural features with their homologs, suggesting similar functions to those in other species.

Assembly of Bacillus subtilis Dynamin into Membrane-Protective Structures in Response to Environmental Stress Is Mediated by Moderate Changes in Dynamics at a Single Molecule Level

Dynamin-like proteins are membrane-associated GTPases, conserved in bacteria and in eukaryotes, that can mediate nucleotide-driven membrane deformation or membrane fusion reactions. Bacillus subtilis' DynA has been shown to play an important role in protecting cells against chemicals that induce membrane leakage, and to form an increased number of membrane-associated structures after induction of membrane stress. We have studied the dynamics of DynA at a single molecule level in real time, to investigate how assembly of stress-induced structures is accompanied by changes in molecule dynamics. We show that DynA molecule displacements are best described by the existence of three distinct populations, a static mode, a low-mobility, and a fast-mobile state. Thus, DynA is most likely freely diffusive within the cytosol, moves along the cell membrane with a low mobility, and arrests at division sites or at stress-induced lesions at the membrane. In response to stress-inducing membrane leakage, but not to general stress, DynA molecules become slightly more static, but largely retain their mobility, suggesting that only few molecules are involved in the repair of membrane lesions, while most molecules remain in a dynamic mode scanning for lesions. Our data suggest that even moderate changes in single molecule dynamics can lead to visible changes in protein localization patterns.

Role of Clathrin and Dynamin in Clathrin Mediated Endocytosis/Synaptic Vesicle Recycling and Implications in Neurological Diseases

Endocytosis is a process essential to the health and well-being of cell. It is required for the internalisation and sorting of “cargo”—the macromolecules, proteins, receptors and lipids of cell signalling. Clathrin mediated endocytosis (CME) is one of the key processes required for cellular well-being and signalling pathway activation. CME is key role to the recycling of synaptic vesicles [synaptic vesicle recycling (SVR)] in the brain, it is pivotal to signalling across synapses enabling intracellular communication in the sensory and nervous systems. In this review we provide an overview of the general process of CME with a particular focus on two key proteins: clathrin and dynamin that have a central role to play in ensuing successful completion of CME. We examine these two proteins as they are the two endocytotic proteins for which small molecule inhibitors, often of known mechanism of action, have been identified. Inhibition of CME offers the potential to develop therapeutic interventions into conditions involving defects in CME. This review will discuss the roles and the current scope of inhibitors of clathrin and dynamin, providing an insight into how further developments could affect neurological disease treatments.

NgCAM and VAMP2 reveal that direct delivery and dendritic degradation maintain axonal polarity

Neurons are polarized cells of extreme scale and compartmentalization. To fulfill their role in electrochemical signaling, axons must maintain a specific complement of membrane proteins. Despite being the subject of considerable attention, the trafficking pathway of axonal membrane proteins is not well understood. Two pathways, direct delivery and transcytosis, have been proposed. Previous studies reached contradictory conclusions about which of these mediates delivery of axonal membrane proteins to their destination, in part because they evaluated long-term distribution changes and not vesicle transport. We developed a novel strategy to selectively label vesicles in different trafficking pathways and determined the trafficking of two canonical axonal membrane proteins, neuron-glia cell adhesion molecule and vesicle-associated membrane protein-2. Results from detailed quantitative analyses of transporting vesicles differed substantially from previous studies and found that axonal membrane proteins overwhelmingly undergo direct delivery. Transcytosis plays only a minor role in axonal delivery of these proteins. In addition, we identified a novel pathway by which wayward axonal proteins that reach the dendritic plasma membrane are targeted to lysosomes. These results redefine how axonal proteins achieve their polarized distribution, a crucial requirement for elucidating the underlying molecular mechanisms.

Blocked O-GlcNAc cycling alters mitochondrial morphology, function, and mass

O-GlcNAcylation is a prevalent form of glycosylation that regulates proteins within the cytosol, nucleus, and mitochondria. The O-GlcNAc modification can affect protein cellular localization, function, and signaling interactions. The specific impact of O-GlcNAcylation on mitochondrial morphology and function has been elusive. In this manuscript, the role of O-GlcNAcylation on mitochondrial fission, oxidative phosphorylation (Oxphos), and the activity of electron transport chain (ETC) complexes were evaluated. In a cellular environment with hyper O-GlcNAcylation due to the deletion of O-GlcNAcase (OGA), mitochondria showed a dramatic reduction in size and a corresponding increase in number and total mitochondrial mass. Because of the increased mitochondrial content, OGA knockout cells exhibited comparable coupled mitochondrial Oxphos and ATP levels when compared to WT cells. However, we observed reduced protein levels for complex I and II when comparing normalized mitochondrial content and reduced linked activity for complexes I and III when examining individual ETC complex activities. In assessing mitochondrial fission, we observed increased amounts of O-GlcNAcylated dynamin-related protein 1 (Drp1) in cells genetically null for OGA and in glioblastoma cells. Individual regions of Drp1 were evaluated for O-GlcNAc modifications, and we found that this post-translational modification (PTM) was not limited to the previously characterized residues in the variable domain (VD). Additional modification sites are predicted in the GTPase domain, which may influence enzyme activity. Collectively, these results highlight the impact of O-GlcNAcylation on mitochondrial dynamics and ETC function and mimic the changes that may occur during glucose toxicity from hyperglycemia.

Dictyostelium Dynamin Superfamily GTPases Implicated in Vesicle Trafficking and Host-Pathogen Interactions

The haploid social amoeba Dictyostelium discoideum is a powerful model organism to study vesicle trafficking, motility and migration, cell division, developmental processes, and host cell-pathogen interactions. Dynamin superfamily proteins (DSPs) are large GTPases, which promote membrane fission and fusion, as well as membrane-independent cellular processes. Accordingly, DSPs play crucial roles for vesicle biogenesis and transport, organelle homeostasis, cytokinesis and cell-autonomous immunity. Major progress has been made over the last years in elucidating the function and structure of mammalian DSPs. D. discoideum produces at least eight DSPs, which are involved in membrane dynamics and other processes. The function and structure of these large GTPases has not been fully explored, despite the elaborate genetic and cell biological tools available for D. discoideum. In this review, we focus on the current knowledge about mammalian and D. discoideum DSPs, and we advocate the use of the genetically tractable amoeba to further study the role of DSPs in cell and infection biology. Particular emphasis is put on the virulence mechanisms of the facultative intracellular bacterium Legionella pneumophila.

Pyrimidyn-Based Dynamin Inhibitors as Novel Cytotoxic Agents

Five focused libraries of pyrimidine-based dynamin GTPase inhibitors, in total 69 compounds were synthesised, and their dynamin inhibition and broad-spectrum cytotoxicity examined. Dynamin plays a crucial role in mitosis, and as such inhibition of dynamin was expected to broadly correlate with the observed cytotoxicity. The pyrimidines synthesised ranged from mono-substituted to trisubstituted. The highest levels of dynamin inhibition were noted with di- and tri- substituted pyrimidines, especially those with pendent amino alkyl chains. Short chains and simple heterocyclic rings reduced dynamin activity. There were three levels of dynamin activity noted: 1-10, 10-25 and 25-60 μM. Screening of these compounds in a panel of cancer cell lines: SW480 (colon), HT29 (colon), SMA (spontaneous murine astrocytoma), MCF-7 (breast), BE2-C (glioblastoma), SJ-G2 (neuroblastoma), MIA (pancreas), A2780 (ovarian), A431 (skin), H460 (lung), U87 (glioblastoma) and DU145 (prostate) cell lines reveal a good correlation between the observed dynamin inhibition and the observed cytotoxicity. The most active analogues (31 a,b) developed returned average GI₅₀ values of 1.0 and 0.78 μM across the twelve cell lines examined. These active analogues were: N² -(3-dimethylaminopropyl)-N⁴ -dodecyl-6-methylpyrimidine-2,4-diamine (31 a) and N⁴ -(3-dimethylaminopropyl)-N² -dodecyl-6-methylpyrimidine-2,4-diamine (31 b).

Shutting the gate: targeting endocytosis in acute leukemia

Endocytosis entails selective packaging of cell surface cargos in cytoplasmic vesicles, thereby controlling key intrinsic cellular processes as well as the response of normal and malignant cells to their microenvironment. The purpose of this review is to outline the latest advances in the development of endocytosis-targeting therapeutic strategies in hematological malignancies.

CryoEM structure of the super-constricted two-start dynamin 1 filament

Dynamin belongs to the large GTPase superfamily, and mediates the fission of vesicles during endocytosis. Dynamin molecules are recruited to the neck of budding vesicles to assemble into a helical collar and to constrict the underlying membrane. Two helical forms were observed: the one-start helix in the constricted state and the two-start helix in the super-constricted state. Here we report the cryoEM structure of a super-constricted two-start dynamin 1 filament at 3.74 Å resolution. The two strands are joined by the conserved GTPase dimeric interface. In comparison with the one-start structure, a rotation around Hinge 1 is observed, essential for communicating the chemical power of the GTPase domain and the mechanical force of the Stalk and PH domain onto the underlying membrane. The Stalk interfaces are well conserved and serve as fulcrums for adapting to changing curvatures. Relative to one-start, small rotations per interface accumulate to bring a drastic change in the helical pitch. Elasticity theory rationalizes the diversity of dynamin helical symmetries and suggests corresponding functional significance.