Transcending membrane barriers: advances in membrane engineering to enhance the production capacity of microbial cell factories.

Microbial cell factories serve as pivotal platforms for the production of high-value natural products, which tend to accumulate on the cell membrane due to their hydrophobic properties. However, the limited space of the cell membrane presents a bottleneck for the accumulation of these products. To enhance the production of intracellular natural products and alleviate the burden on the cell membrane caused by product accumulation, researchers have implemented various membrane engineering strategies. These strategies involve modifying the membrane components and structures of microbial cell factories to achieve efficient accumulation of target products. This review summarizes recent advances in the application of membrane engineering technologies in microbial cell factories, providing case studies involving Escherichia coli and yeast. Through these strategies, researchers have not only improved the tolerance of cells but also optimized intracellular storage space, significantly enhancing the production efficiency of natural products. This article aims to provide scientific evidence and references for further enhancing the efficiency of similar cell factories.

Exploiting the roles of nitrogen sources for HEA increment in Cordyceps cicadae.

Cordyceps cicadae, as a new food ingredient, is a valuable edible and medicinal fungi. However, its resources are severely depleted due to environmental limitations and excessive harvesting practices. N6-(2-hydroxyethyl) adenosine (HEA), as an important product of Cordyceps cicadae, has the potential to be used in medical industry due to its diverse disease curing potential. However, the disclosure of HEA synthesis still severely limited its application until now. In this study, the kinetic curves for adenosine and HEA under shaker fermentation were explored. The kinetics of HEA and adenosine production exhibited a competitive pattern, implicating a possibility of sharing a same step during their synthesis. Due to HEA as a derivative of nitrogen metabolism, the effect of different nitrogen sources (peptone, yeast extract, ammonium sulfate, diammonium oxalate monohydrate, ammonium citrate dibasic, and ammonium citrate tribasic) on HEA production in Cordyceps cicadae strain AH 10-4 had been explored under different incubation conditions (shaker fermentation, stationary fermentation, and submerged fermentation). Our results indicated that the complex organic nitrogen sources were found to improve the accumulation of HEA content under shaker fermentation. In contrast, the optimal nitrogen source for the accumulation of HEA under stationary fermentation and submerged fermentation was ammonium citrate tribasic. But submerged fermentation obviously shortened the incubation time and had a comparable capacity of HEA accumulation by 2.578 mg/g compared with stationary fermentation of 2.535 mg/g, implicating a possibility of scaled-up production of HEA in industry by submerged fermentation. Based on the dramatic HEA production by ammonium sulfate as nitrogen resources between stationary and shaker fermentations, alanine, aspartate and glutamate as well as arginine metabolic pathway were related to the production of HEA by comparative transcriptome. Further investigation indicated that glutamic acid, which is an analog of Asp, showed an optimum production of HEA in comparison with other amino acids.

Utilization of CRISPR-Cas genome editing technology in filamentous fungi: function and advancement potentiality.

Filamentous fungi play a crucial role in environmental pollution control, protein secretion, and the production of active secondary metabolites. The evolution of gene editing technology has significantly improved the study of filamentous fungi, which in the past was laborious and time-consuming. But recently, CRISPR-Cas systems, which utilize small guide RNA (sgRNA) to mediate clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (Cas), have demonstrated considerable promise in research and application for filamentous fungi. The principle, function, and classification of CRISPR-Cas, along with its application strategies and research progress in filamentous fungi, will all be covered in the review. Additionally, we will go over general matters to take into account when editing a genome with the CRISPR-Cas system, including the creation of vectors, different transformation methodologies, multiple editing approaches, CRISPR-mediated transcriptional activation (CRISPRa) or interference (CRISPRi), base editors (BEs), and Prime editors (PEs).

[Sterol transport proteins in yeast: a review].

Sterols are a class of cyclopentano-perhydrophenanthrene derivatives widely present in living organisms. Sterols are important components of cell membranes. In addition, they also have important physiological and pharmacological activities. With the development of synthetic biology and metabolic engineering technology, yeast cells are increasingly used for the heterologous synthesis of sterols in recent years. Nevertheless, since sterols are hydrophobic macromolecules, they tend to accumulate in the membrane fraction of yeast cells and consequently trigger cytotoxicity, which hampers the further improvement of sterols yield. Therefore, revealing the mechanism of sterol transport in yeast, especially understanding the working principle of sterol transporters, is vital for designing strategies to relieve the toxicity of sterol accumulation and increasing sterol yield in yeast cell factories. In yeast, sterols are mainly transported through protein-mediated non-vesicular transport mechanisms. This review summarizes five types of sterol transport-related proteins that have been reported in yeast, namely OSBP/ORPs family proteins, LAM family proteins, ABC transport family proteins, CAP superfamily proteins, and NPC-like sterol transport proteins. These transporters play important roles in intracellular sterol gradient distribution and homeostasis maintenance. In addition, we also review the current status of practical applications of sterol transport proteins in yeast cell factories.

Salmonella effector SopB reorganizes cytoskeletal vimentin to maintain replication vacuoles for efficient infection.

A variety of intracellular bacteria modulate the host cytoskeleton to establish subcellular niches for replication. However, the role of intermediate filaments, which are crucial for mechanical strength and resilience of the cell, and in bacterial vacuole preservation remains unclear. Here, we show that Salmonella effector SopB reorganizes the vimentin network to form cage-like structures that surround Salmonella-containing vacuoles (SCVs). Genetic removal of vimentin markedly disrupts SCV organization, significantly reduces bacterial replication and cell death. Mechanistically, SopB uses its N-terminal Cdc42-binding domain to interact with and activate Cdc42 GTPase, which in turn recruits vimentin around SCVs. A high-content imaging-based screening identified that MEK1/2 inhibition led to vimentin dispersion. Our work therefore elucidates the signaling axis SopB-Cdc42-MEK1/2 as mobilizing host vimentin to maintain concrete SCVs and identifies a mechanism contributing to Salmonella replication. Importantly, Trametinib, a clinically-approved MEK1/2 inhibitor identified in the screen, displayed significant anti-infection efficacy against Salmonella both in vitro and in vivo, and may provide a therapeutic option for treating drug-tolerant salmonellosis.

Simulation of integrated anaerobic digestion-gasification systems using machine learning models.

In this study, the anaerobic digestion model M-ADM1 was integrated with the gasification model T-ANN to form a set of integrated models that can efficiently simulate the biomass AD-GS integration technology. Biogas slurry is used as feedstocks to prepare biogas slurry fertilizer. Solid residue is used feedstocks for gasification reactions. Biogas and syngas from the gasification of solid residue are used for energy. In this process, carbon emission is regarded as an important index for the comprehensive evaluation and optimization of AD-GS integration process. This study found that when the anaerobic digestion duration was 0 to 15 days, the carbon emission reduction increased rapidly. The amount of carbon emission reduction peaks on day 15. The value of carbon emission reduction is 0.1828 gCO2eq. In addition, when FEAG reached the maximum value at 15 days of anaerobic digestion, the decreasing trend of FEAG rate change value started to become significant.

Falsochrobactrum tianjinense sp. nov., a New Petroleum-Degrading Bacteria Isolated from Oily Soils.

The microbial remediation technology had great potential and attracted attention to total petroleum hydrocarbon pollution (TPH) remediation, but its efficiency is limited by its application in the field. In this study, a new TPH-degrading strain, TDYN1, was isolated from contaminated oil soil in Dagang Oilfield in Tianjin, China, and identified as Falsochrobactrum sp. by 16S rRNA sequence analysis. The physiological characterization of the isolate was observed. The orthogonal experiment was carried out for the optimum degradation conditions to improve its biodegradation efficiency. The strain was the gram-stain-negative, short rod-shaped, non-spore-forming, designated Falsochrobactrum tianjinense sp. nov (strain TDYN1); it had 3.51 Mb, and the DNA G + C content of the strain was 56.0%. The degradation rate of TDYN1 was 69.95% after 7 days of culture in optimal degradation conditions (temperature = 30 °C, pH = 8, salinity = 10 g L-1, petroleum concentration = 1 g L-1, and the inoculation dose of strain TDYN1 = 6%) and also reached more than 30% under other relatively extreme conditions. It suggested that the TDYN1 has great potential for TPH remediation in the soils of North China.

[Design of Biochemistry PBL teaching cases suitable for engineering education].

Engineering education is an important part of China's higher education. With the deepening of the connotation of new engineering talents training, it is timely to carry out the curriculum reform in all directions and improve the quality of engineering talents. In order to highlight the characteristics of fostering new engineering talents, specialized courses and practical courses are becoming the focus of curriculum teaching reform. However to this end, it is urgent to explore how to strengthen fostering talents with engineering characteristics in the professional foundation courses. Taking the biochemistry course as an example, problem-based learning teaching methods were employed, appropriate teaching cases were selected, scientific and technical problems based instructional designs were explored, and students were guided to condense, analyze and solve problems. This study aims to transform the learning attitude of students from "passive" to "active", enhance students' thinking skills, highlight the engineering application of science and technology, lay the foundation for continuous and even lifelong learning, and provide a reference for fostering talents under the new engineering background.

Label-free relative quantitative proteomics reveals extracellular vesicles as a vehicle for Salmonella effector protein delivery.

Extracellular vesicles are small vesicles with a diameter of 30-150 nm that are actively secreted by eukaryotic cells and play important roles in intercellular communication, immune responses, and tumorigenesis. Previous studies have shown that extracellular vesicles are involved in the process of Salmonella enterica serovar Typhimurium (S. Typhimurium) infection. However, changes in the protein content of extracellular vesicles elicited by S. Typhimurium infection have not been determined. Here, we extracted the extracellular vesicles with high purity from S. Typhimurium-infected Henle-407 cells, a kind of human intestinal epithelial cells, by ultracentrifugation combined with an extracellular vesicles purification kit, and analyzed their protein composition using label-free relative quantitative proteomics. The extracted extracellular vesicles exhibited an oval vesicular structure under electron microscopy, with a mean diameter of 140.4 ± 32.4 nm. The exosomal marker proteins CD9, CD63, and HSP70 were specifically detected. Compared with the uninfected group, nearly 1,234 specifically loaded proteins were uncovered in S. Typhimurium-infected Henle-407 cells. Among them were 409 S. Typhimurium-derived specific proteins, indicating a significant alteration in protein composition of extracellular vesicles by S. Typhimurium infection. Notably, these proteins included 75 secretory proteins and over 300 non-secretory proteins of S. Typhimurium, implicating novel pathways for bacterial protein delivery, although it remains unclear if their loading into extracellular vesicles is active or passive. To investigate the roles of these extracellular proteins, we exemplified the function of SopB, a well-known T3SS effector protein, and showed that the extracellular SopB could be taken up by RAW264.7 macrophages, activating the phosphorylation of Akt. This study provides new insights into the mechanism of Salmonella infection through extracellular vesicles that transport virulence proteins to uninfected neighboring cells to facilitate further infection.

Analysis of Internal and External Microorganism Community of Wild Cicada Flowers and Identification of the Predominant Cordyceps cicadae Fungus.

The parasitoid fungus Cordyceps cicadae, whose fruiting bodies are known in China as "chan hua," literally "cicada flower," has been used as a traditional Chinese medicinal ingredient for centuries. However, systematic disclosure of the vital factors responsible for the formation of wild cicada flower is limited. Here, we determined the physicochemical properties of soil and simultaneously analyzed the diversities and the structures of microbial community inhabiting the coremia, sclerotia, and soil around wild cicada flowers through high-throughput sequencing. Our results indicated that cicada flower more preferentially occurred in acidic soil (pH 5.9) with abundant moisture content (MC), total nitrogen (TN), and organic matter (OM). The dominant fungal genera in soil mainly included Isaria, f__Clavariaceae_Unclassified, Umbelopsis, f__Chaetomiaceae_Unclassified, Mortierella, f__Sordariaceae_Unclassified, and Arcopilus. Among them, C. cicadae was the only fungus that was massively detected in both the coremia and sclerotia with abundance of 83.5 and 53.6%, respectively. Based on this, a C. cicadae strain named AH10-4 with excellent adenosine- and N 6-(2-hydroxyethyl)-adenosine (HEA)-producing capability was successfully isolated. However, to the aspect of bacteria, Burkholderia-Caballeronia-Paraburkholderia, Bacillus, Acidibacter, f__Xanthobacteraceae_Unclassified, and Candidatus_Solibacter were the dominant genera in soil. Pedobacter, f__Enterobacteriaceae_Unclassified, Pandoraea, Achromobacter, Stenotrophomonas, Burkholderia-Caballeronia-Paraburkholderia, and Chitinophaga were the dominant genera in the coremia and sclerotia. Notably, Burkholderia-Caballeronia-Paraburkholderia was the shared bacteria among them with high abundance of 3.1, 11.4, and 5.2% in the sclerotia, coremia, and soil, respectively. However, the possible role of these bacteria to the occurrence of cicada flower has been unclear to our knowledge. By analyzing the correlation between physicochemical properties and microbial community of soil, we found that MC, Fe, and Zn were significantly negatively correlated with soil Isaria and that Cu was significantly negatively correlated with most dominant soil bacterial genera. But Mg was significantly positively correlated with most dominant taxa. This study provides new insight into the formation mechanisms of cicada flower and may contribute to the large-scale cultivation of cicada flowers.

Types of nuclear localization signals and mechanisms of protein import into the nucleus.

Nuclear localization signals (NLS) are generally short peptides that act as a signal fragment that mediates the transport of proteins from the cytoplasm into the nucleus. This NLS-dependent protein recognition, a process necessary for cargo proteins to pass the nuclear envelope through the nuclear pore complex, is facilitated by members of the importin superfamily. Here, we summarized the types of NLS, focused on the recently reported related proteins containing nuclear localization signals, and briefly summarized some mechanisms that do not depend on nuclear localization signals into the nucleus. Video Abstract.

New Insights Into the Biosynthesis of Typical Bioactive Components in the Traditional Chinese Medicinal Fungus Cordyceps militaris.

Cordyceps militaris, a traditional medicinal ingredient with a long history of application in China, is regarded as a high-value fungus due to its production of various bioactive ingredients with a wide range of pharmacological effects in clinical treatment. Several typical bioactive ingredients, such as cordycepin, D-mannitol, cordyceps polysaccharides, and N6-(2-hydroxyethyl)-adenosine (HEA), have received increasing attention due to their antitumor, antioxidant, antidiabetic, radioprotective, antiviral and immunomodulatory activities. Here, we systematically sorted out the latest research progress on the chemical characteristics, biosynthetic gene clusters and pathways of these four typical bioactive ingredients. This summary will lay a foundation for obtaining low-cost and high-quality bioactive ingredients in large amounts using microbial cell factories in the future.

Whole-Genome-Based Survey for Polyphyletic Serovars of Salmonella enterica subsp. enterica Provides New Insights into Public Health Surveillance.

Serotyping has traditionally been considered the basis for surveillance of Salmonella, but it cannot distinguish distinct lineages sharing the same serovar that vary in host range, pathogenicity and epidemiology. However, polyphyletic serovars have not been extensively investigated. Public health microbiology is currently being transformed by whole-genome sequencing (WGS) data, which promote the lineage determination using a more powerful and accurate technique than serotyping. The focus in this study is to survey and analyze putative polyphyletic serovars. The multi-locus sequence typing (MLST) phylogenetic analysis identified four putative polyphyletic serovars, namely, Montevideo, Bareilly, Saintpaul, and Muenchen. Whole-genome-based phylogeny and population structure highlighted the polyphyletic nature of Bareilly and Saintpaul and the multi-lineage nature of Montevideo and Muenchen. The population of these serovars was defined by extensive genetic diversity, the open pan genome and the small core genome. Source niche metadata revealed putative existence of lineage-specific niche adaptation (host-preference and environmental-preference), exhibited by lineage-specific genomic contents associated with metabolism and transport. Meanwhile, differences in genetic profiles relating to virulence and antimicrobial resistance within each lineage may contribute to pathogenicity and epidemiology. The results also showed that recombination events occurring at the H1-antigen loci may be an important reason for polyphyly. The results presented here provide the genomic basis of simple, rapid, and accurate identification of phylogenetic lineages of these serovars, which could have important implications for public health.

In vitro and in vivo cancer cell apoptosis triggered by competitive binding of Cinchona alkaloids to the RING domain of TRAF6.

TRAF6 is highly expressed in many tumors and plays an important role in the immune system. The aim of this study is to confirm anti-tumor activities of all naturally occurring Cinchona alkaloids that have been screened using computational docking program, and to validate the accuracy and specificity of the RING domain of TRAF6 as a potential anti-tumor target, and to explore their effect on the immune system. Results reported herein would demonstrate that Cinchona alkaloids could induce apoptosis in HeLa cells, inhibit the ubiquitination and phosphorylation of both AKT and TAK1, and up-regulate the ratio of Bax/Bcl-2. In addition, these compounds could induce apoptosis in vivo, and increase the secretion of TNF-α, IFN-γ, and IgG, while not significantly impacting the ratio of CD4+T/CD8+T. These investigations suggest that the RING domain of TRAF6 could serve as a de novo biological target for therapeutic treatment in cancers.

The prognostic value of p62 in solid tumor patients: a meta-analysis.

p62, as a scaffolding/adaptor protein, is involved in multiple physiological processes include inflammation, autophagy and mitosis. However, the influence of p62 in cancer patients has not been comprehensively investigated. Moreover, the prognostic value of p62 for the survival of patients with solid tumors remains controversial. In this present meta-analysis, twenty suitable articles were identified from PubMed, EMBASE and Web of Science, Nature databases, including 4271 patients. A random-effect or fixed-effect model was adopted to correlate p62 expression with different outcome measured in entire tumors. Combined with results of hazard ratios (HRs) and 95% confidence intervals (CIs), we concluded that higher expression of p62 is associated with poorer overall survival (OS) (HR: 2.22, 95% CI: 1.82-2.71, P < 0.05), disease-free survival (DFS) (HR = 2.48, 95% CI: 1.78-3.46, P < 0.05) and even certain clinicopathological parameters, such as lymph node metastasis (RR = 1.21, 95% CI: 1.06-1.37) and clinical stages (RR = 1.27, 95% CI: 1.12-1.45), in cancer patients. Consequently, our data showed that p62 might be an effective poor prognostic factor for patients with various solid tumors.

The prognostic value of over-expressed TrkB in solid tumors: a systematic review and meta-analysis.

It is reported recently Tropomyosin-related receptor Kinase B (TrkB) plays key roles in the anoikis resistance during the processes of tumorigenesis and metastasis. However, its prognostic significance for clinical patients remains inconclusive. In order to establish a correct and practicable link between increased TrkB and prognostication of human solid tumors, a meta-analysis was performed in this article. A systematic literature research in the electronic databases PubMed, Embase and Web of Science was performed to identify eligible studies. A fixed-effects meta-analytical model was employed to correlate TrkB expression with OS, DFS and clinicopathological features. A total of 11 studies covering 1516 patients with various solid tumors were recruited in this meta-analysis. TrkB over-expression was associated with poorer OS and poorer DFS in multivariate analysis. Additionally, the pooled odds ratios (ORs) indicated that TrkB over-expression was associated with large tumor size, lymph node metastasis, distant metastasis and a higher clinical stage. Overall, these results indicated that TrkB over-expression in patients with solid tumors might be related to poor prognosis and serve as a potential predictive marker of poor clinicopathological prognosis factor.

Draft genome sequence of broad-spectrum antibiotic sparsomycin-producing Streptomyces sparsogenes ATCC 25498 from the American Type Culture Collection.

OBJECTIVES: Sparsomycin, which exhibits rare broad-spectrum antibiotic and antitumour activity against bacteria, Archaea, Eucarya and various cancer cell lines, has been widely used as a powerful tool to study protein synthesis. Here we report the draft genome sequence of Streptomyces sparsogenes ATCC 25498 from the American Type Culture Collection (ATCC), which has become an organism of interest owing to its ability to produce sparsomycin. METHODS: The whole-genome sequence of S. sparsogenes ATCC 25498 was determined using a high-throughput Illumina HiSeq 2000 platform and genome assembly was performed using the SOAPdenovo method. RESULTS: Whole-genome sequencing analysis revealed a genome size of 10.0Mb. A total of 41 secondary metabolite biosynthetic gene clusters were identified. The gene cluster for the biosynthesis of sparsomycin was localised on scaffold 9. CONCLUSIONS: The genome sequence of S. sparsogenes ATCC 25498 will not only aid in understanding the regulatory mechanism of sparsomycin biosynthesis but will also reveal the ability of the isolate to produce novel bioactive secondary metabolites.

Tumor Necrosis Factor Receptor-Associated Factor 6 (TRAF6) Mediates Ubiquitination-Dependent STAT3 Activation upon Salmonella enterica Serovar Typhimurium Infection.

Salmonella enterica serovar Typhimurium can inject effector proteins into host cells via type III secretion systems (T3SSs). These effector proteins modulate a variety of host transcriptional responses to facilitate bacterial growth and survival. Here we show that infection of host cells with S Typhimurium specifically induces the ubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6). This TRAF6 ubiquitination is triggered by the Salmonella pathogenicity island 1 (SPI-1) T3SS effectors SopB and SopE2. We also demonstrate that TRAF6 is involved in the SopB/SopE2-induced phosphorylation of signal transducer and activator of transcription 3 (STAT3), a signaling event conducive to the intracellular growth of S Typhimurium. Specifically, TRAF6 mediates lysine-63 ubiquitination within the Src homology 2 (SH2) domain of STAT3, which is an essential step for STAT3 membrane recruitment and subsequent phosphorylation in response to S Typhimurium infection. TRAF6 ubiquitination participates in STAT3 phosphorylation rather than serving as only a hallmark of E3 ubiquitin ligase activation. Our results reveal a novel strategy in which S Typhimurium T3SS effectors broaden their functions through the activation of host proteins in a ubiquitination-dependent manner to manipulate host cells into becoming a Salmonella-friendly zone.

Upregulated SOX9 expression indicates worse prognosis in solid tumors: a systematic review and meta-analysis.

It was recently reported that increased SOX9 expression drives tumor growth and promotes cancer invasion during human tumorigenicity and metastasis. However, the prognostic value of SOX9 for the survival of patients with solid tumors remains controversial. The present meta-analysis was thus performed to highlight the link between dysregulated SOX9 expression and prognosis in cancer patients. A systematic literature search was conducted using the electronic databases PubMed, Web of Science and Embase to identify eligible studies. A random-effects meta-analytical model was employed to correlate SOX9 expression with overall survival (OS), disease-free survival (DFS) and clinicopathological features. In total, 17 studies with 3307 patients were eligible for the final analysis. Combined hazard ratios (HRs) and 95% confidence intervals (CIs) suggested that high SOX9 expression has an unfavourable impact on OS (HR = 1.66, 95% CI 1.36-2.02, P < 0.001) and DFS (HR = 3.54, 95% CI 2.29-5.47, P = 0.008) in multivariate analysis. Additionally, the pooled odds ratios (ORs) indicated that SOX9 over-expression is associated with large tumor size, lymph node metastasis, distant metastasis and a higher clinical stage. Overall, these results indicated that SOX9 over-expression in patients with solid tumors might be related to poor prognosis and could serve as a potential predictive marker of poor clinicopathological prognosis factor.

The Salmonella effector SopB prevents ROS-induced apoptosis of epithelial cells by retarding TRAF6 recruitment to mitochondria.

Microbial pathogens enter host cells by injecting effector proteins of the Type III secretion system (T3SS), which facilitate pathogen translocation across the host cell membrane. These effector proteins exert their effects by modulating a variety of host innate immune responses, thereby facilitating bacterial replication and systemic infection. Salmonella enterica serovar typhimurium (S.typhimurium) is a clinically important pathogen that causes food poisoning and gastroenteritis. The SopB effector protein of S. typhimurium, encoded by Salmonella pathogenicity islands (SPI)-1 T3SS, protects host epithelial cells from infection-induced apoptosis. However, how SopB influences apoptosis induction remains unclear. Here, we investigated the mechanism of SopB action in host cells. We found that SopB inhibits infection-induced apoptosis by attenuating the production of reactive oxygen species (ROS) in mitochondria, the crucial organelles for apoptosis initiation. Further investigation revealed that SopB binds to cytosolic tumor necrosis factor receptor associated factor 6 (TRAF6) and forms a trap preventing the mitochondrial recruitment of TRAF6, an essential event for ROS generation within mitochondria. By studying the response of Traf6(+/+) and Traf6(-/-)mouse embryonic fibroblasts to S. typhimurium infection, we found that TRAF6 promoted apoptosis by increasing ROS accumulation, which led to increased Bax/Bcl-2 ratio, Bax recruitment to mitochondrial membrane, and release of Cyt c into the cytoplasm. These findings show that SopB suppresses host cell apoptosis by binding to TRAF6 and preventing mitochondrial ROS generation.