VDAC and its interacting partners in plant and animal systems: an overview

Bombyx mori voltage-dependent anion-selective channel induces programmed cell death to defend against Bombyx mori nucleopolyhedrovirus infection

BACKGROUND

Voltage-dependent anion-selective channels (VDACs) serve as pore proteins within the mitochondrial membrane, aiding in the regulation of cell life and cell death. Although the occurrence of cell death is crucial for defense against virus infection, the function played by VDAC in Bombyx mori, in response to the influence of Bombyx mori nucleopolyhedrovirus (BmNPV), remains unclear.

RESULTS

BmVDAC was found to be relatively highly expressed both during embryonic development, and in the Malpighian tubule and midgut. Additionally, the expression levels of BmVDAC were found to be different among silkworm strains with varying levels of resistance to BmNPV, strongly suggesting a connection between BmVDAC and virus infection. To gain further insight into the function of BmVDAC in BmNPV, we employed RNA interference (RNAi) to silence and overexpress it by pIZT/V5-His-mCherry. The results revealed that BmVDAC is instrumental in developing the resistance of host cells to BmNPV infection in BmN cell-line cells, which was further validated as likely to be associated with initiating programmed cell death (PCD). Furthermore, we evaluated the function of BmVDAC in another insect, Spodoptera exigua. Knockdown of the BmVDAC homolog in S. exigua, SeVDAC, made the larvae more sensitive to BmNPV.

CONCLUSION

We have substantiated the pivotal role of BmVDAC in conferring resistance against BmNPV infection, primarily associated with the initiation of PCD. The findings of this study shine new light on the molecular mechanisms governing the silkworm's response to BmNPV infection, thereby supporting innovative approaches for pest biocontrol. © 2024 Society of Chemical Industry.

The role and mechanism of VDAC1 in type 2 diabetes: An underestimated target of environmental pollutants

Type 2 diabetes (T2D) is a chronic metabolic disease that accounts for more than 90% of diabetic patients. Its main feature is hyperglycemia due to insulin resistance or insulin deficiency. With changes in diet and lifestyle habits, the incidence of T2D in adolescents has burst in recent decades. The deterioration in the exposure to the environmental pollutants further aggravates the prevalence of T2D, and consequently, it imposes a significant economic burden. Therefore, early prevention and symptomatic treatment are essential to prevent diabetic complications. Mitochondrial number and electron transport chain activity are decreased in the patients with T2D. Voltage-Dependent Anion Channel 1 (VDAC1), as a crucial channel protein on the outer membrane of mitochondria, regulates signal transduction between mitochondria and other cellular components, participating in various biological processes. When VDAC1 exists in oligomeric form, it additionally facilitates the entry and exit of macromolecules into and from mitochondria, modulating insulin secretion. We summarize and highlight the interplay between VDAC1 and T2D, especially in the environmental pollutants-related T2D, shed light on the potential therapeutic implications of targeting VDAC1 monomers and oligomers, providing a new possible target for the treatment of T2D.

Insecticidal Activity and Molecular Target by Morphological Analysis, RNAseq, and Molecular Docking of the Aryltetralin Lignan Lactone Helioxanthin, Isolated from Taiwania flousiana Gaussen

Botanical insecticides are considered an environmentally friendly approach to insect control because they are easily biodegraded and cause less environmental pollution compared to traditional chemical pesticides. In this study, we reported the insecticidal activities of the ingredients from Taiwania flousiana Gaussen (T. flousiana). Five compounds, namely helioxanthin (C1), taiwanin E (C2), taiwanin H (C3), 7,4'-dimethylamentoflavone (C4), and 7,7″-di-O-methylamentoflavone (C5), were isolated and tested against the second, third, and fourth instar larvae of Aedes aegypti. Our results indicated that all five compounds showed insecticidal activities, and helioxanthin, which is an aryltetralin lignan lactone, was the most effective with LC50 values of 0.60, 2.82, and 3.12 mg/L, respectively, 48 h after application, with its activity against the second instar larvae similar to that of pyrethrin and better than that of rotenone. Further studies found that helioxanthin accumulated in the gastric cecum and the midgut and caused swelling of mitochondria with shallow matrices and fewer or disappeared crista. Additionally, our molecular mechanisms studies indicated that the significantly differentially expressed genes (DEGs) were mainly associated with mitochondria and the cuticle, among which the voltage-dependent anion-selective channel (VDAC) gene was the most down-regulated by helioxanthin, and VDAC is the potential target of helioxanthin by binding to specific amino acid residues (His 122 and Glu 147) via hydrogen bonds. We conclude that aryltetralin lignan lactone is a potential class of novel insecticides by targeting VDAC.

Empowering mitochondrial metabolism: Exploring L-lactate supplementation as a promising therapeutic approach for metabolic syndrome

Mitochondrial dysfunction plays a critical role in the pathogenesis of metabolic syndrome (MetS), affecting various cell types and organs. In MetS animal models, mitochondria exhibit decreased quality control, characterized by abnormal morphological structure, impaired metabolic activity, reduced energy production, disrupted signaling cascades, and oxidative stress. The aberrant changes in mitochondrial function exacerbate the progression of metabolic syndrome, setting in motion a pernicious cycle. From this perspective, reversing mitochondrial dysfunction is likely to become a novel and powerful approach for treating MetS. Unfortunately, there are currently no effective drugs available in clinical practice to improve mitochondrial function. Recently, L-lactate has garnered significant attention as a valuable metabolite due to its ability to regulate mitochondrial metabolic processes and function. It is highly likely that treating MetS and its related complications can be achieved by correcting mitochondrial homeostasis disorders. In this review, we comprehensively discuss the complex relationship between mitochondrial function and MetS and the involvement of L-lactate in regulating mitochondrial metabolism and associated signaling pathways. Furthermore, it highlights recent findings on the involvement of L-lactate in common pathologies of MetS and explores its potential clinical application and further prospects, thus providing new insights into treatment possibilities for MetS.

Mitochondrial VOLTAGE-DEPENDENT ANION CHANNEL 3 regulates stomatal closure by abscisic acid signaling

In Arabidopsis (Arabidopsis thaliana), stomatal closure mediated by abscisic acid (ABA) is redundantly controlled by ABA receptor family proteins (PYRABACTIN RESISTANCE 1 [PYR1]/PYR1-LIKE [PYLs]) and subclass III SUCROSE NONFERMENTING 1 (SNF1)-RELATED PROTEIN KINASES 2 (SnRK2s). Among these proteins, the roles of PYR1, PYL2, and SnRK2.6 are more dominant. A recent discovery showed that ABA-induced accumulation of reactive oxygen species (ROS) in mitochondria promotes stomatal closure. By analyzing stomatal movements in an array of single and higher order mutants, we revealed that the mitochondrial protein VOLTAGE-DEPENDENT ANION CHANNEL 3 (VDAC3) jointly regulates ABA-mediated stomatal closure with a specialized set of PYLs and SnRK2s by affecting cellular and mitochondrial ROS accumulation. VDAC3 interacted with 9 PYLs and all 3 subclass III SnRK2s. Single mutation in VDAC3, PYLs (except PYR1 and PYL2), or SnRK2.2/2.3 had little effect on ABA-mediated stomatal closure. However, knocking out PYR1, PYL1/2/4/8, or SnRK2.2/2.3 in vdac3 mutants resulted in significantly delayed or attenuated ABA-mediated stomatal closure, despite the presence of other PYLs or SnRK2s conferring redundant functions. We found that cellular and mitochondrial accumulation of ROS induced by ABA was altered in vdac3pyl1 mutants. Moreover, H2O2 treatment restored ABA-induced stomatal closure in mutants with decreased stomatal sensitivity to ABA. Our work reveals that VDAC3 ensures redundant control of ABA-mediated stomatal closure by canonical ABA signaling components.

Voltage-dependent anion channel 3 (VDAC3) mediates P. syringae induced ABA-SA signaling crosstalk in Arabidopsis thaliana

Pathogen severely affects plant mitochondrial processes including respiration, however, the roles and mechanism of mitochondrial protein during the immune response remain largely unexplored. The interplay of plant hormone signaling during defense is an outcome of plant pathogen interaction. We recently discovered that the Arabidopsis calcineurin B-like interacting protein kinase 9 (AtCIPK9) interacts with the voltage-dependent anion channel 3 (AtVDAC3) and inhibits MV-induced oxidative damage. Here we report the characterization of AtVDAC3 in an antagonistic interaction pathway between abscisic acid (ABA) and salicylic acid (SA) signaling in Pseudomonas syringae -Arabidopsis interaction. In this study, we observed that mutants of AtVDAC3 were highly susceptible to Pseudomonas syringae infection as compared to the wild type (WT) Arabidopsis plants. Transcripts of VDAC3 and CIPK9 were inducible upon ABA application. Following pathogen exposure, expression analyses of ABA and SA biosynthesis genes indicated that the function of VDAC3 is required for isochorisimate synthase 1 (ICS1) expression but not for Nine-cis-epoxycaotenoid dioxygenase 3 (NCED3) expression. Despite the fact that vdac3 mutants had increased NCED3 expression in response to pathogen challenge, transcripts of ABA sensitive genes such as AtRD22 and AtRAB18 were downregulated even after exogenous ABA application. VDAC3 is required for ABA responsive genes expression upon exogenous ABA application. We also found that Pseudomonas syringae-induced SA signaling is downregulated in vdac3 mutants since overexpression of VDAC3 resulted in hyperaccumulation of Pathogenesis related gene1 (PR1) transcript. Interestingly, ABA application prior to P. syringae inoculation resulted in the upregulation of ABA responsive genes like Responsive to ABA18 (RAB18) and Responsive to dehydration 22 (RD22). Intriguingly, in the absence of AtVDAC3, Pst challenge can dramatically increase ABA-induced RD22 and RAB18 expression. Altogether our results reveal a novel Pathogen-SA-ABA interaction pathway in plants. Our findings show that ABA plays a significant role in modifying plant-pathogen interactions, owing to cross-talk with the biotic stress signaling pathways of ABA and SA.

Lipidomic insights into the response of Arabidopsis sepals to mild heat stress

Arabidopsis sepals coordinate flower opening in the morning as ambient temperature rises; however, the underlying molecular mechanisms are poorly understood. Mutation of one heat shock protein encoding gene, HSP70-16, impaired sepal heat stress responses (HSR), disrupting lipid metabolism, especially sepal cuticular lipids, leading to abnormal flower opening. To further explore, to what extent, lipids play roles in this process, in this study, we compared lipidomic changes in sepals of hsp70-16 and vdac3 (mutant of a voltage-dependent anion channel, VDAC3, an HSP70-16 interactor) grown under both normal (22 °C) and mild heat stress (27 °C, mild HS) temperatures. Under normal temperature, neither hsp70-16 nor vdac3 sepals showed significant changes in total lipids; however, vdac3 but not hsp70-16 sepals exhibited significant reductions in the ratios of all detected 11 lipid classes, except the monogalactosyldiacylglycerols (MGDGs). Under mild HS temperature, hsp70-16 but not vdac3 sepals showed dramatic reduction in total lipids. In addition, vdac3 sepals exhibited a significant accumulation of plastidic lipids, especially sulfoquinovosyldiacylglycerols (SQDGs) and phosphatidylglycerols (PGs), whereas hsp70-16 sepals had a significant accumulation of triacylglycerols (TAGs) and simultaneous dramatic reductions in SQDGs and phospholipids (PLs), such as phosphatidylcholines (PCs), phosphatidylethanolamines (PEs), and phosphatidylserines (PSs). These findings revealed that the impact of mild HS on sepal lipidome is influenced by genetic factors, and further, that HSP70-16 and VDAC3 differently affect sepal lipidomic responses to mild HS. Our studies provide a lipidomic insight into functions of HSP and VDAC proteins in the plant's HSR, in the context of floral development.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-023-00103-x.

Causes and consequences of endogenous hypoxia on growth and metabolism of developing maize kernels

Maize (Zea mays) kernels are the largest cereal grains, and their endosperm is severely oxygen deficient during grain fill. The causes, dynamics, and mechanisms of acclimation to hypoxia are minimally understood. Here, we demonstrate that hypoxia develops in the small, growing endosperm, but not the nucellus, and becomes the standard state, regardless of diverse structural and genetic perturbations in modern maize (B73, popcorn, sweet corn), mutants (sweet4c, glossy6, waxy), and non-domesticated wild relatives (teosintes and Tripsacum species). We also uncovered an interconnected void space at the chalazal pericarp, providing superior oxygen supply to the placental tissues and basal endosperm transfer layer. Modeling indicated a very high diffusion resistance inside the endosperm, which, together with internal oxygen consumption, could generate steep oxygen gradients at the endosperm surface. Manipulation of oxygen supply induced reciprocal shifts in gene expression implicated in controlling mitochondrial functions (23.6 kDa Heat-Shock Protein, Voltage-Dependent Anion Channel 2) and multiple signaling pathways (core hypoxia genes, cyclic nucleotide metabolism, ethylene synthesis). Metabolite profiling revealed oxygen-dependent shifts in mitochondrial pathways, ascorbate metabolism, starch synthesis, and auxin degradation. Long-term elevated oxygen supply enhanced the rate of kernel development. Altogether, evidence here supports a mechanistic framework for the establishment of and acclimation to hypoxia in the maize endosperm.

Effect of the metal ion-induced carbonylation modification of mitochondrial membrane channel protein VDAC on cell vitality, seedling growth and seed aging

Introduction

Seeds are the most important carrier of germplasm preservation. However, an irreversible decrease in vigor can occur after the maturation of seeds, denoted as seed aging. Mitochondrion is a crucial organelle in initiation programmed cell death during seed aging. However, the underlying mechanism remains unclear.

Methods

Our previous proteome study found that 13 mitochondria proteins underwent carbonylation modification during the aging of Ulmus pumila L. (Up) seeds. This study detected metal binding proteins through immobilized metal affinity chromatography (IMAC), indicating that metal binding proteins in mitochondria are the main targets of carbonization during seed aging. Biochemistry, molecular and cellular biology methods were adopted to detect metal-protein binding, protein modification and subcellular localization. Yeast and Arabidopsis were used to investigate the biological functions in vivo.

Results and discussion

In IMAC assay, 12 proteins were identified as Fe²+/Cu²+/Zn²+ binding proteins, including mitochondrial voltage dependent anion channels (VDAC). UpVDAC showed binding abilities to all the three metal ions. His204Ala (H204A) and H219A mutated UpVDAC proteins lost their metal binding ability, and became insensitive to metal-catalyzed oxidation (MCO) induced carbonylation. The overexpression of wild-type UpVDAC made yeast cells more sensitive to oxidative stress, retarded the growth of Arabidopsis seedlings and accelerated the seed aging, while overexpression of mutated UpVDAC weakened these effects of VDAC. These results reveal the relationship between the metal binding ability and carbonylation modification, as well as the probable function of VDAC in regulating cell vitality, seedling growth and seed aging.

Molecular response and evolution of plant anion transport systems to abiotic stress

We propose that anion channels are essential players for green plants to respond and adapt to the abiotic stresses associated changing climate via reviewing the literature and analyzing the molecular evolution, comparative genetic analysis, and bioinformatics analysis of the key anion channel gene families. Climate change-induced abiotic stresses including heatwave, elevated CO₂, drought, and flooding, had a major impact on plant growth in the last few decades. This scenario could lead to the exposure of plants to various stresses. Anion channels are confirmed as the key factors in plant stress responses, which exist in the green lineage plants. Numerous studies on anion channels have shed light on their protein structure, ion selectivity and permeability, gating characteristics, and regulatory mechanisms, but a great quantity of questions remain poorly understand. Here, we review function of plant anion channels in cell signaling to improve plant response to environmental stresses, focusing on climate change related abiotic stresses. We investigate the molecular response and evolution of plant slow anion channel, aluminum-activated malate transporter, chloride channel, voltage-dependent anion channel, and mechanosensitive-like anion channel in green plant. Furthermore, comparative genetic and bioinformatic analysis reveal the conservation of these anion channel gene families. We also discuss the tissue and stress specific expression, molecular regulation, and signaling transduction of those anion channels. We propose that anion channels are essential players for green plants to adapt in a diverse environment, calling for more fundamental and practical studies on those anion channels towards sustainable food production and ecosystem health in the future.

CIPK9 targets VDAC3 and modulates oxidative stress responses in Arabidopsis

Calcium (Ca²⁺ ) is widely recognized as a key second messenger in mediating various plant adaptive responses. Here we show that calcineurin B-like interacting protein kinase CIPK9 along with its interacting partner VDAC3 identified in the present study are involved in mediating plant responses to methyl viologen (MV). CIPK9 physically interacts with and phosphorylates VDAC3. Co-localization, co-immunoprecipitation, and fluorescence resonance energy transfer experiments proved their physical interaction in planta. Both cipk9 and vdac3 mutants exhibited a tolerant phenotype against MV-induced oxidative stress, which coincided with the lower-level accumulation of reactive oxygen species in their roots. In addition, the analysis of cipk9vdac3 double mutant and VDAC3 overexpressing plants revealed that CIPK9 and VDAC3 were involved in the same pathway for inducing MV-dependent oxidative stress. The response to MV was suppressed by the addition of lanthanum chloride, a non-specific Ca²⁺ channel blocker indicating the role of Ca²⁺ in this pathway. Our study suggest that CIPK9-VDAC3 module may act as a key component in mediating oxidative stress responses in Arabidopsis.

The Mitochondrial Ca2+ import complex is altered in ADPKD

Mutations in either of the polycystic kidney disease genes, PKD1 or PKD2, engender the growth of cysts, altering renal function. Cystic growth is supported by major changes in cellular metabolism, some of which involve the mitochondrion, a major storage site for Ca²⁺ and a key organelle in cellular Ca²⁺ signaling. The goal here was to understand the role of components of the mitochondrial Ca²⁺ uptake complex in PC1-mutant cells in autosomal dominant polycystic kidney disease (ADPKD). We found that the mitochondrial Ca²⁺ uniporter (MCU) and voltage-dependent anion channels 1& 3 (VDAC) were down-regulated in different mouse and cell models of ADPKD along with the Ca²⁺-dependent enzyme, pyruvate dehydrogenase phosphatase (PDHX). The release of Ca²⁺ from the endoplasmic reticulum, and Ca²⁺ uptake by the mitochondria were upregulated in PC1(polycystin)-null cells. We also observed an enhanced staining with MitoTracker Red CMXRos in PC1-null cultured cells than in PC1-containing cells and a substantially higher increase in response to ER Ca²⁺ release. Increased colocalization of the Ca²⁺ sensitive dye, rhodamine2, with MitoTracker Green suggested an increase Ca²⁺ entry into the mitochondria in PC1 null cells subsequent to Ca²⁺ release from the ER or from Ca²⁺ entry from the extracellular solution. These data clearly demonstrate abnormal release of Ca²⁺ by the ER and corresponding alterations in Ca²⁺ uptake by the mitochondria in PC1^-null cells. Importantly, inhibiting mitochondrial Ca²⁺ uptake with the specific inhibitor Ru360 inhibited cyst growth and altered both apoptosis and cell proliferation. We further show that the decrease in mitochondrial proteins and abnormally high Ca²⁺ signaling can be reversed by application of the cystic fibrosis (CFTR) corrector, VX-809. We conclude that enhanced Ca²⁺ signaling and alterations in proteins association with the mitochondrial Ca²⁺ uptake complex are associated with malfunction of PC1. Finally, our results identify novel therapeutic targets for treating ADPKD.

Overexpression of a Voltage-Dependent Anion-Selective Channel (VDAC) Protein-Encoding Gene, MsVDAC, from Medicago sativa Confers Cold and Drought Tolerance to Transgenic Tobacco

Voltage-dependent anion channels (VDACs) are highly conserved proteins that are involved in the translocation of tRNA and play a key role in modulating plant senescence and multiple pathways. However, the functions of VDACs in plants are still poorly understood. Here, a novel VDAC gene was isolated and identified from alfalfa (Medicago sativa L.). MsVDAC localized to the mitochondria, and its expression was highest in alfalfa roots and was induced in response to cold, drought and salt treatment. Overexpression of MsVDAC in tobacco significantly increased MDA, GSH, soluble sugars, soluble protein and proline contents under cold and drought stress. However, the activities of SOD and POD decreased in transgenic tobacco under cold stress, while the O2- content increased. Stress-responsive genes including LTP1, ERD10B and Hxk3 were upregulated in the transgenic plants under cold and drought stress. However, GAPC, CBL1, BI-1, Cu/ZnSOD and MnSOD were upregulated only in the transgenic tobacco plants under cold stress, and GAPC, CBL1, and BI-1 were downregulated under drought stress. These results suggest that MsVDAC provides cold tolerance by regulating ROS scavenging, osmotic homeostasis and stress-responsive gene expression in plants, but the improved drought tolerance via MsVDAC may be mainly due to osmotic homeostasis and stress-responsive genes.

Adverse Effects of Metformin From Diabetes to COVID-19, Cancer, Neurodegenerative Diseases, and Aging: Is VDAC1 a Common Target?

Metformin has been used for treating diabetes mellitus since the late 1950s. In addition to its antihyperglycemic activity, it was shown to be a potential drug candidate for treating a range of other diseases that include various cancers, cardiovascular diseases, diabetic kidney disease, neurodegenerative diseases, renal diseases, obesity, inflammation, COVID-19 in diabetic patients, and aging. In this review, we focus on the important aspects of mitochondrial dysfunction in energy metabolism and cell death with their gatekeeper VDAC1 (voltage-dependent anion channel 1) as a possible metformin target, and summarize metformin’s effects in several diseases and gut microbiota. We question how the same drug can act on diseases with opposite characteristics, such as increasing apoptotic cell death in cancer, while inhibiting it in neurodegenerative diseases. Interestingly, metformin’s adverse effects in many diseases all show VDAC1 involvement, suggesting that it is a common factor in metformin-affecting diseases. The findings that metformin has an opposite effect on various diseases are consistent with the fact that VDAC1 controls cell life and death, supporting the idea that it is a target for metformin.

VDAC Modulation of Cancer Metabolism: Advances and Therapeutic Challenges

Most anionic metabolites including respiratory substrates, glycolytic adenosine triphosphate (ATP), and small cations that enter mitochondria, and mitochondrial ATP moving to the cytosol, cross the outer mitochondrial membrane (OMM) through voltage dependent anion channels (VDAC). The closed states of VDAC block the passage of anionic metabolites, and increase the flux of small cations, including calcium. Consequently, physiological or pharmacological regulation of VDAC opening, by conditioning the magnitude of both anion and cation fluxes, is a major contributor to mitochondrial metabolism. Tumor cells display a pro-proliferative Warburg phenotype characterized by enhanced aerobic glycolysis in the presence of partial suppression of mitochondrial metabolism. The heterogeneous and flexible metabolic traits of most human tumors render cells able to adapt to the constantly changing energetic and biosynthetic demands by switching between predominantly glycolytic or oxidative phenotypes. Here, we describe the biological consequences of changes in the conformational state of VDAC for cancer metabolism, the mechanisms by which VDAC-openers promote cancer cell death, and the advantages of VDAC opening as a valuable pharmacological target. Particular emphasis is given to the endogenous regulation of VDAC by free tubulin and the effects of VDAC-tubulin antagonists in cancer cells. Because of its function and location, VDAC operates as a switch to turn-off mitochondrial metabolism (closed state) and increase aerobic glycolysis (pro-Warburg), or to turn-on mitochondrial metabolism (open state) and decrease glycolysis (anti-Warburg). A better understanding of the role of VDAC regulation in tumor progression is relevant both for cancer biology and for developing novel cancer chemotherapies.

Cellular Interactome of Mitochondrial Voltage-Dependent Anion Channels: Oligomerization and Channel (Mis)Regulation

Voltage-dependent anion channels (VDACs) of the outer mitochondrial membrane are known conventionally as metabolite flux proteins. However, research findings in the past decade have revealed the multifaceted regulatory roles of VDACs, from governing cellular physiology and mitochondria-mediated apoptosis to directly regulating debilitating cancers and neurodegenerative diseases. VDACs achieve these diverse functions by establishing isoform-dependent stereospecific interactomes in the cell with the cytosolic constituents and endoplasmic reticulum complexes, and the machinery of the mitochondrial compartments. VDACs are now increasingly recognized as regulatory hubs of the cell. Not surprisingly, even the transient misregulation of VDACs results directly in mitochondrial dysfunction. Additionally, human VDACs are now implicated in interaction with aggregation-prone cytosolic proteins, including Aβ, tau, and α-synuclein, contributing directly to the onset of Alzheimer's and Parkinson's diseases. Deducing the interaction dynamics and mechanisms can lead to VDAC-targeted peptide-based therapeutics that can alleviate neurodegenerative states. This review succinctly presents the latest findings of the VDAC interactome, and the mode(s) of VDAC-dependent regulation of biochemical physiology. We also discuss the relevance of VDACs in pathophysiological states and aggregation-associated diseases and address how VDACs will facilitate the development of next-generation precision medicines.

TSPO protein binding partners in bacteria, animals, and plants

The ancient membrane protein TSPO is phylogenetically widespread from archaea and bacteria to insects, vertebrates, plants, and fungi. TSPO’s primary amino acid sequence is only modestly conserved between diverse species, although its five transmembrane helical structure appears mainly conserved. Its cellular location and orientation in membranes have been reported to vary between species and tissues, with implications for potential diverse binding partners and function. Most TSPO functions relate to stress-induced changes in metabolism, but in many cases it is unclear how TSPO itself functions—whether as a receptor, a sensor, a transporter, or a translocator. Much evidence suggests that TSPO acts indirectly by association with various protein binding partners or with endogenous or exogenous ligands. In this review, we focus on proteins that have most commonly been invoked as TSPO binding partners. We suggest that TSPO was originally a bacterial receptor/stress sensor associated with porphyrin binding as its most ancestral function and that it later developed additional stress-related roles in eukaryotes as its ability to bind new partners evolved.

The reference genome and transcriptome of the limestone langur, Trachypithecus leucocephalus, reveal expansion of genes related to alkali tolerance

Background

Trachypithecus leucocephalus, the white-headed langur, is a critically endangered primate that is endemic to the karst mountains in the southern Guangxi province of China. Studying the genomic and transcriptomic mechanisms underlying its local adaptation could help explain its persistence within a highly specialized ecological niche.

Results

In this study, we used PacBio sequencing and optical assembly and Hi-C analysis to create a high-quality de novo assembly of the T. leucocephalus genome. Annotation and functional enrichment revealed many genes involved in metabolism, transport, and homeostasis, and almost all of the positively selected genes were related to mineral ion binding. The transcriptomes of 12 tissues from three T. leucocephalus individuals showed that the great majority of genes involved in mineral absorption and calcium signaling were expressed, and their gene families were significantly expanded. For example, FTH1 primarily functions in iron storage and had 20 expanded copies.

Conclusions

These results increase our understanding of the evolution of alkali tolerance and other traits necessary for the persistence of T. leucocephalus within an ecologically unique limestone karst environment.

VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease

Voltage-dependent anion channel (VDAC), the most abundant mitochondrial outer membrane protein, is important for a variety of mitochondrial functions including metabolite exchange, calcium transport, and apoptosis. While VDAC's role in shuttling metabolites between the cytosol and mitochondria is well established, there is a growing interest in understanding the mechanisms of its regulation of mitochondrial calcium transport. Here we review the current literature on VDAC's role in calcium signaling, its biophysical properties, physiological function, and pathology focusing on its importance in cardiac diseases. We discuss the specific biophysical properties of the three VDAC isoforms in mammalian cells-VDAC 1, 2, and 3-in relationship to calcium transport and their distinct roles in cell physiology and disease. Highlighting the emerging evidence that cytosolic proteins interact with VDAC and regulate its calcium permeability, we advocate for continued investigation into the VDAC interactome at the contact sites between mitochondria and organelles and its role in mitochondrial calcium transport.

On the Detection and Functional Significance of the Protein-Protein Interactions of Mitochondrial Transport Proteins

Protein-protein assemblies are highly prevalent in all living cells. Considerable evidence has recently accumulated suggesting that particularly transient association/dissociation of proteins represent an important means of regulation of metabolism. This is true not only in the cytosol and organelle matrices, but also at membrane surfaces where, for example, receptor complexes, as well as those of key metabolic pathways, are common. Transporters also frequently come up in lists of interacting proteins, for example, binding proteins that catalyze the production of their substrates or that act as relays within signal transduction cascades. In this review, we provide an update of technologies that are used in the study of such interactions with mitochondrial transport proteins, highlighting the difficulties that arise in their use for membrane proteins and discussing our current understanding of the biological function of such interactions.