Flux regulation through glycolysis and respiration is balanced by inositol pyrophosphates in yeast.

Although many prokaryotes have glycolysis alternatives, it's considered as the only energy-generating glucose catabolic pathway in eukaryotes. Here, we managed to create a hybrid-glycolysis yeast. Subsequently, we identified an inositol pyrophosphatase encoded by OCA5 that could regulate glycolysis and respiration by adjusting 5-diphosphoinositol 1,2,3,4,6-pentakisphosphate (5-InsP7) levels. 5-InsP7 levels could regulate the expression of genes involved in glycolysis and respiration, representing a global mechanism that could sense ATP levels and regulate central carbon metabolism. The hybrid-glycolysis yeast did not produce ethanol during growth under excess glucose and could produce 2.68 g/L free fatty acids, which is the highest reported production in shake flask of Saccharomyces cerevisiae. This study demonstrated the significance of hybrid-glycolysis yeast and determined Oca5 as an inositol pyrophosphatase controlling the balance between glycolysis and respiration, which may shed light on the role of inositol pyrophosphates in regulating eukaryotic metabolism.

The CRL5-SPSB3 ubiquitin ligase targets nuclear cGAS for degradation.

Cyclic GMP-AMP synthase (cGAS) senses aberrant DNA during infection, cancer and inflammatory disease, and initiates potent innate immune responses through the synthesis of 2'3'-cyclic GMP-AMP (cGAMP)1-7. The indiscriminate activity of cGAS towards DNA demands tight regulatory mechanisms that are necessary to maintain cell and tissue homeostasis under normal conditions. Inside the cell nucleus, anchoring to nucleosomes and competition with chromatin architectural proteins jointly prohibit cGAS activation by genomic DNA8-15. However, the fate of nuclear cGAS and its role in cell physiology remains unclear. Here we show that the ubiquitin proteasomal system (UPS) degrades nuclear cGAS in cycling cells. We identify SPSB3 as the cGAS-targeting substrate receptor that associates with the cullin-RING ubiquitin ligase 5 (CRL5) complex to ligate ubiquitin onto nuclear cGAS. A cryo-electron microscopy structure of nucleosome-bound cGAS in a complex with SPSB3 reveals a highly conserved Asn-Asn (NN) minimal degron motif at the C terminus of cGAS that directs SPSB3 recruitment, ubiquitylation and cGAS protein stability. Interference with SPSB3-regulated nuclear cGAS degradation primes cells for type I interferon signalling, conferring heightened protection against infection by DNA viruses. Our research defines protein degradation as a determinant of cGAS regulation in the nucleus and provides structural insights into an element of cGAS that is amenable to therapeutic exploitation.

The XRN1-regulated RNA helicase activity of YTHDC2 ensures mouse fertility independently of m6A recognition.

The functional consequence of N6-methyladenosine (m6A) RNA modification is mediated by "reader" proteins of the YTH family. YTH domain-containing 2 (YTHDC2) is essential for mammalian fertility, but its molecular function is poorly understood. Here, we identify U-rich motifs as binding sites of YTHDC2 on 3' UTRs of mouse testicular RNA targets. Although its YTH domain is an m6A-binder in vitro, the YTH point mutant mice are fertile. Significantly, the loss of its 3'→5' RNA helicase activity causes mouse infertility, with the catalytic-dead mutation being dominant negative. Biochemical studies reveal that the weak helicase activity of YTHDC2 is enhanced by its interaction with the 5'→3' exoribonuclease XRN1. Single-cell transcriptomics indicate that Ythdc2 mutant mitotic germ cells transition into meiosis but accumulate a transcriptome with mixed mitotic/meiotic identity that fail to progress further into meiosis. Finally, our demonstration that ythdc2 mutant zebrafish are infertile highlights its conserved role in animal germ cell development.

Stimulus-specific hypothalamic encoding of a persistent defensive state.

Persistent neural activity in cortical, hippocampal, and motor networks has been described as mediating working memory for transiently encountered stimuli1,2. Internal emotional states, such as fear, also persist following exposure to an inciting stimulus3, but it is unclear whether slow neural dynamics are involved in this process. Neurons in the dorsomedial and central subdivisions of the ventromedial hypothalamus (VMHdm/c) that express the nuclear receptor protein NR5A1 (also known as SF1) are necessary for defensive responses to predators in mice4-7. Optogenetic activation of these neurons, referred to here as VMHdmSF1 neurons, elicits defensive behaviours that outlast stimulation5,8, which suggests the induction of a persistent internal state of fear or anxiety. Here we show that in response to naturalistic threatening stimuli, VMHdmSF1 neurons in mice exhibit activity that lasts for many tens of seconds. This persistent activity was correlated with, and required for, persistent defensive behaviour in an open-field assay, and depended on neurotransmitter release from VMHdmSF1 neurons. Stimulation and calcium imaging in acute slices showed that there is local excitatory connectivity between VMHdmSF1 neurons. Microendoscopic calcium imaging of VMHdmSF1 neurons revealed that persistent activity at the population level reflects heterogeneous dynamics among individual cells. Unexpectedly, distinct but overlapping VMHdmSF1 subpopulations were persistently activated by different modalities of threatening stimulus. Computational modelling suggests that neither recurrent excitation nor slow-acting neuromodulators alone can account for persistent activity that maintains stimulus identity. Our results show that stimulus-specific slow neural dynamics in the hypothalamus, on a time scale orders of magnitude longer than that of working memory in the cortex9,10, contribute to a persistent emotional state.

Robust miniature Cas-based transcriptional modulation by engineering Un1Cas12f1 and tethering Sso7d.

The miniature V-F CRISPR-Cas12f system has been repurposed for gene editing and transcription modulation. The small size of Cas12f satisfies the packaging capacity of adeno-associated virus (AAV) for gene therapy. However, the efficiency of Cas12f-mediated transcriptional activation varies among different target sites. Here, we developed a robust miniature Cas-based transcriptional activation or silencing system using Un1Cas12f1. We engineered Un1Cas12f1 and the cognate guide RNA and generated miniCRa, which led to a 1,319-fold increase in the activation of the ASCL1 gene. The activity can be further increased by tethering DNA-binding protein Sso7d to miniCRa and generating SminiCRa, which reached a 5,628-fold activation of the ASCL1 gene and at least hundreds-fold activation at other genes examined. We adopted these mutations of Un1Cas12f1 for transcriptional repression and generated miniCRi or SminiCRi, which led to the repression of ∼80% on average of eight genes. We generated an all-in-one AAV vector AIOminiCRi used to silence the disease-related gene SERPINA1. AIOminiCRi AAVs led to the 70% repression of the SERPINA1 gene in the Huh-7 cells. In summary, miniCRa, SminiCRa, miniCRi, and SminiCRi are robust miniature transcriptional modulators with high specificity that expand the toolbox for biomedical research and therapeutic applications.

An extended conformation of SARS-CoV-2 main protease reveals allosteric targets.

SignificanceThe coronavirus main protease (Mpro) is required for viral replication. Here, we obtained the extended conformation of the native monomer of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Mpro by trapping it with nanobodies and found that the catalytic domain and the helix domain dissociate, revealing allosteric targets. Another monomeric state is termed compact conformation and is similar to one protomer of the dimeric form. We designed a Nanoluc Binary Techonology (NanoBiT)-based high-throughput allosteric inhibitor assay based on structural conformational change. Our results provide insight into the maturation, dimerization, and catalysis of the coronavirus Mpro and pave a way to develop an anticoronaviral drug through targeting the maturation process to inhibit the autocleavage of Mpro.

Twisted DNA Origami-Based Chiral Monolayers for Spin Filtering.

DNA monolayers with inherent chirality play a pivotal role across various domains including biosensors, DNA chips, and bioelectronics. Nonetheless, conventional DNA chiral monolayers, typically constructed from single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA), often lack structural orderliness and design flexibility at the interface. Structural DNA nanotechnology has emerged as a promising solution to tackle these challenges. In this study, we present a strategy for crafting highly adaptable twisted DNA origami-based chiral monolayers. These structures exhibit distinct interfacial assembly characteristics and effectively mitigate the structural disorder of dsDNA monolayers, which is constrained by a limited persistence length of ∼50 nm of dsDNA. We highlight the spin-filtering capabilities of seven representative DNA origami-based chiral monolayers, demonstrating a maximal one-order-of-magnitude increase in spin-filtering efficiency per unit area compared with conventional dsDNA chiral monolayers. Intriguingly, our findings reveal that the higher-order tertiary chiral structure of twisted DNA origami further enhances the spin-filtering efficiency. This work paves the way for the rational design of DNA chiral monolayers.

NIR Fluorescent/Photoacoustic Bimodal Imaging of Ferroptosis in Pancreatic Cancer Using Biothiols-Activable Probes.

Ferroptosis modulation is a powerful therapeutic option for pancreatic ductal adenocarcinoma (PDAC) with a low 5-year survival rate and lack of effective treatment methods. However, due to the dual role of ferroptosis in promoting and inhibiting pancreatic tumorigenesis, regulating the degree of ferroptosis is very important to obtain the best therapeutic effect of PDAC. Biothiols are suitable as biomarkers of imaging ferroptosis due to the dramatic decreases of biothiol levels in ferroptosis caused by the inhibited synthesis pathway of glutathione (GSH) and the depletion of biothiol by reactive oxygen species. Moreover, a very recent study reported that cysteine (Cys) depletion can lead to pancreatic tumor ferroptosis in mice and may be employed as an effective therapeutic strategy for PDAC. Therefore, visualization of biothiols in ferroptosis of PDAC will be helpful for regulating the degree of ferroptosis, understanding the mechanism of Cys depletion-induced pancreatic tumor ferroptosis, and further promoting the study and treatment of PDAC. Herein, two biothiol-activable near-infrared (NIR) fluorescent/photoacoustic bimodal imaging probes (HYD-BX and HYD-DX) for imaging of pancreatic tumor ferroptosis were reported. These two probes show excellent bimodal response performances for biothiols in solution, cells, and tumors. Subsequently, they have been employed successfully for real-time visualization of changes in concentration levels of biothiols during the ferroptosis process in PDAC cells and HepG2 cells. Most importantly, they have been further applied for bimodal imaging of ferroptosis in pancreatic cancer in mice, with satisfactory results. The development of these two probes provides new tools for monitoring changes in concentration levels of biothiols in ferroptosis and will have a positive impact on understanding the mechanism of Cys depletion-induced pancreatic tumor ferroptosis and further promoting the study and treatment of PDAC.

Nanobodies as negative allosteric modulators for human calcium sensing receptor.

Human calcium sensing receptor (CaSR) senses calcium ion concentrations in vivo and is an important class of drug targets. Mutations in the receptor can lead to disorders of calcium homeostasis, including hypercalcemia and hypocalcemia. Here, 127 CaSR-targeted nanobodies were generated from camels, and four nanobodies with inhibitory function were further identified. Among these nanobodies, NB32 can effectively inhibit the mobilization of intracellular calcium ions (Ca2+i) and suppress the G12/13 and ERK1/2 signaling pathways downstream of CaSR. Moreover, it enhanced the inhibitory effect of the calcilytics as a negative allosteric modulator (NAM). We determined the structure of complex and found NB32 bound to LB2 (Ligand-binding 2) domain of CaSR to prevent the interaction of LB2 domains of two protomers to stabilize the inactive state of CaSR.

Generation of SARS-CoV-2 spike receptor binding domain mutants and functional screening for immune evaders using a novel lentivirus-based system.

The emergence of rapid and continuous mutations of severe acute respiratory syndrome 2 (SARS-CoV-2) spike glycoprotein that increased with the Omicron variant points out the necessity to anticipate such mutations for conceiving specific and adaptable therapies to avoid another pandemic. The crucial target for the antibody treatment and vaccine design is the receptor binding domain (RBD) of the SARS-CoV-2 spike. It is also the site where the virus has shown its high ability to mutate and consequently escape immune response. We developed a robust and simple method for generating a large number of functional SARS-CoV-2 spike RBD mutants by error-prone PCR and a novel nonreplicative lentivirus-based system. We prepared anti-RBD wild type (WT) polyclonal antibodies and used them to screen and select for mutant libraries that escape inhibition of virion entry into recipient cells expressing human angiotensin-converting enzyme 2 and transmembrane serine protease 2. We isolated, cloned, and sequenced six mutants totally bearing nine mutation sites. Eight mutations were found in successive WT variants, including Omicron and other recombinants, whereas one is novel. These results, together with the detailed functional analyses of two mutants provided the proof of concept for our approach.

Isomerization of surface functionalized SWCNTs and the critical influence on photoluminescence: static calculations and excited-state dynamics simulations.

Single-walled carbon nanotubes (SWCNTs) functionalized with sparse surface chemical groups are promising for a variety of optical applications such as quantum information and bio-imaging. However, the luminescence efficiencies and stability, two key aspects, undoubtedly govern their practical usage. Herein, we assess the surface migration of oxygen and triazine groups on as-modified SWCNT fragments by adopting transition state theory and explore the de-excitation of oxygen-functionalized SWCNT fragments by performing non-adiabatic excited-state dynamics simulations. According to the predicted moderate or even small reaction barriers, the migration of both oxygen and triazine groups is feasible from an sp3 defect configuration forming an energetically more stable sp2 configuration at moderate or even room temperatures. Such isomerization leads to drastically different light emission capabilities as indicated by the large or zero oscillator strengths. During the dynamics simulations, the lowest excited singlet (S1) state rapidly decays in energy within 20 fs and then fluctuates until the end, providing insights into the emission mechanism of SWCNTs. This study highlights the potential intrinsic limitations of surface-functionalized SWCNTs for luminescence applications.

Annonaceous Acetogenins Synergistically Inhibit Hepatocellular Carcinoma with Sorafenib.

Sorafenib was first approved as the standard treatment for advanced hepatocellular carcinoma (HCC). Despite providing an advantage in terms of patient survival, sorafenib has shown poor clinical efficacy and severe side effects after long-term treatment. Thus, combination treatment is a potential way to increase the effectiveness and reduce the dose-limiting toxicity of sorafenib. Extracts of the seeds of Annona montana have shown synergistic antitumor activity with sorafenib, and seven annonaceous acetogenins, including three new acetogenins, muricin P (2), muricin Q (3), and muricin R (4), were isolated from the extracts by bioguided fractionation and showed synergy with sorafenib. The structures of these compounds were determined using spectroscopic and chemical methods. Annonacin (1) and muricin P (2), which reduced intracellular ATP levels and promoted apoptosis, exhibited synergistic cytotoxicity with sorafenib in vitro. In vivo, annonacin (1) displayed synergistic antitumor activity by promoting tumor cell apoptosis. Moreover, the potential mechanism of annonacin (1) was predicted by transcriptomic analysis, which suggested that SLC33A1 is a potential target in HCC. Annonacin (1) might be a novel candidate for combination therapy with sorafenib against advanced HCC.

Uncovering the Power of HSCCC: Separation of Diastereomeric and Regioisomeric Styrylpyrones from the Stem Bark of Goniothalamus leiocarpus.

The plant Goniothalamus leiocarpus of the Annonaceae family is used as an alternative medicine in tropical regions. Applying high-speed counter current chromatography (HSCCC), eight new bioactive styrylpyrone isomers, including 6R,7S,8R,2'S-goniolactone B (1), 6S,7S,8S,2'S-goniolactone B (2), 6R,7R,8R,2'S-goniolactone B (3), 6R,7S,8S,2'S-goniolactone C (4), 6R,7S,8R,2'S-goniolactone C (5), 6S,7R,8S,2'S-goniolactone C (6), and two positional isomers, 6R,7R,8R,2'S-goniolactone G (7) and 6S,7R,8R,2'S-goniolactone G (8), were isolated from a chloroform fraction (2.1 g) of G. leiocarpus, which had a prominent spot by TLC analysis. The structures of the new compounds were elucidated by MS, NMR, IR, and UV spectra, and their absolute configurations were determined by Mosher's method, ECD, and X-ray diffraction analysis. The isolates are characteristic components found in plants of the genus Goniothalamus and consist of two structural moieties: a styrylpyrone and a dihydroflavone unit. The isolation of the eight new compounds demonstrates the effectiveness of HSCCC in separating the isomers of natural styrylpyrone. In a bioactivity assessment, compounds 1 and 6 exhibited cytotoxic effects against the human colon carcinoma cell lines LS513 and SW620 with IC50 values ranging from 1.6 to 3.9 µM. Compounds 1, 2, 7, and 8 showed significant synergistic activity against antibiotic-resistant Staphylococcus aureus strains.

The impact of apparent temperature on the emergency visits for traumatic fractures in Hangzhou, China.

BACKGROUND: Traumatic fractures occur frequently worldwide. However, research remains limited on the association between short-term exposure to temperature and traumatic fractures. This study aims to explore the impact of apparent temperature (AT) on emergency visits (EVs) due to traumatic fractures. METHODS: Based on EVs data for traumatic fractures and the contemporary meteorological data, a generalized Poisson regression model along with a distributed lag nonlinear model (DLNM) were undertaken to determine the impact of AT on traumatic fracture EVs. Subgroup analysis by gender and age and sensitivity analysis were also performed. RESULTS: A total of 25,094 EVs for traumatic fractures were included in the study. We observed a wide "J"-shaped relationship between AT and risk of traumatic fractures, with AT above 9.5 °C positively associated with EVs due to traumatic fractures. The heat effects became significant at cumulative lag 0-11 days, and the relative risk (RR) for moderate heat (95th percentile, 35.7 °C) and extreme heat (99.5th percentile, 38.8 °C) effect was 1.311 (95% CI: 1.132-1.518) and 1.418 (95% CI: 1.191-1.688) at cumulative lag 0-14 days, respectively. The cold effects were consistently non-significant on single or cumulative lag days across 0-14 days. The heat effects were higher among male and those aged 18-65 years old. The sensitivity analysis results remained robust. CONCLUSION: Higher AT is associated with cumulative and delayed higher traumatic fracture EVs. The male and those aged 18-65 years are more susceptible to higher AT.

Glycyrrhizin attenuates renal inflammation in a mouse Con A-hepatitis model via the IL-25/M2 axis.

Glycyrrhizin (GL) has immunoregulatory effects on various inflammatory diseases including hepatitis and nephritis. However, the mechanisms underlying the anti-inflammatory effect of GL on renal inflammation are not fully understood. Hepatorenal syndrome (HRS) is a functional acute renal impairment that occurs in severe liver disease, and we found that kidney injury also occurs in Con A-induced experimental hepatitis in mice. We previously found that GL can alleviate Con A-induced hepatitis by regulating the expression of IL-25 in the liver. We wanted to investigate whether GL can alleviate Con A-induced nephritis by regulating IL-25. IL-25 regulates inflammation by modulating type 2 immune responses, but the mechanism by which IL-25 affects kidney disease remains unclear. In this study, we found that the administration of GL enhanced the expression of IL-25 in renal tissues; the latter promoted the generation of type 2 macrophages (M2), which inhibited inflammation in the kidney caused by Con A challenge. IL-25 promoted the secretion of the inhibitory cytokine IL-10 by macrophages but inhibited the expression of the inflammatory cytokine IL-1ß by macrophages. Moreover, IL-25 downregulated the Con A-mediated expression of Toll-like receptor (TLR) 4 on macrophages. By comparing the roles of TLR2 and TLR4, we found that TLR4 is required for the immunoregulatory effect of IL-25 on macrophages. Our data revealed that GL has anti-inflammatory effects on Con A-induced kidney injury and that the GL/IL-25/M2 axis participates in the anti-inflammatory process. This study suggested that GL is a potential therapeutic for protecting against acute kidney injury.

Structure basis of two nanobodies neutralizing SARS-CoV-2 Omicron variant by targeting ultra-conservative epitopes.

The evolving SARS-CoV-2 Omicron strain has repeatedly caused widespread disease epidemics, and effective antibody drugs continue to be in short supply. Here, we identified a batch of nanobodies with high affinity for receptor binding domain (RBD) of SARS-CoV-2 spike protein, separated them into three classes using high performance liquid chromatography (HPLC), and then resolved the crystal structure of the ternary complexes of two non-competing nanobodies (NB1C6 and NB1B5) with RBD using X-ray crystallography. The structures showed that NB1B5 and NB1C6 bind to the left and right flank of the RBD, respectively, and that the binding epitopes are highly conserved cryptic sites in all SARS-CoV-2 mutant strains, as well as that NB1B5 can effectively block the ACE2. These two nanobodies were covalently linked into multivalent and bi-paratopic formats, and have a high affinity and neutralization potency for omicron, potentially inhibiting viral escape. The binding sites of these two nanobodies are relatively conserved, which help guide the structural design of antibodies targeting future variants of SARS-CoV-2 to combat COVID-19 epidemics and pandemics.

Micron-Scale Fabrication of Ultrathin Amorphous Copper Nanosheets Templated by DNA Scaffolds.

Two-dimensional (2D) amorphous materials could outperform their crystalline counterparts toward various applications because they have more defects and reactive sites and thus could exhibit a unique surface chemical state and provide an advanced electron/ion transport path. Nevertheless, it is challenging to fabricate ultrathin and large-sized 2D amorphous metallic nanomaterials in a mild and controllable manner due to the strong metallic bonds between metal atoms. Here, we reported a simple yet fast (10 min) DNA nanosheet (DNS)-templated method to synthesize micron-scale amorphous copper nanosheets (CuNSs) with a thickness of 1.9 ± 0.4 nm in aqueous solution at room temperature. We demonstrated the amorphous feature of the DNS/CuNSs by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Interestingly, we found that they could transform to crystalline forms under continuous electron beam irradiation. Of note, the amorphous DNS/CuNSs exhibited much stronger photoemission (∼62-fold) and photostability than dsDNA-templated discrete Cu nanoclusters due to the elevation of both the conduction band (CB) and valence band (VB). Such ultrathin amorphous DNS/CuNSs hold great potential for practical applications in biosensing, nanodevices, and photodevices.

Reaction-Activated Disassembly of the NIR-II Probe Enables Fast Detection and Ratiometric Photoacoustic Imaging of Glutathione In Vivo.

Glutathione (GSH), the most abundant nonprotein biothiol, is a significant endogenous molecule that plays a key role in redox equilibrium in vivo and is regarded as a critical biomarker of cancer. Currently, various fluorescent probes have been designed and synthesized for imaging GSH at the cellular level in the visible range and the first near-infrared window (NIR-I, 750-900 nm). However, the application of these fluorescent probes for bioimaging and biosensing in vivo has been extremely hindered by the high biobackground and low tissue penetration. Herein, based on the self-assembly and disassembly of J-aggregation, we designed and synthesized a GSH-activatable probe MC-PSE for second near-infrared window (NIR-II) fluorescence and ratiometric photoacoustic imaging of GSH in vivo. The anionic cyanine-based MC-PSE tends to form stable J-aggregates in an aqueous solution. Upon the reaction with GSH, the J-aggregates of MC-PSE disassembled, the emission peak intensity of MC-PSE at 940 nm significantly increased by about 20 times, and the PA900/PA980 ratio increased by 4 times within 15 min in vitro. Notably, we used MC-PSE to visualize GSH in tumor-bearing mice and to distinguish normal and tumor areas successfully by virtue of NIR-II FL and PA dual-modal imaging. The design strategy of MC-PSE provides a novel method for ratiometric photoacoustic imaging, and MC-PSE is expected to be a powerful tool for the accurate detection of GSH in cancer diagnosis.

Human Herpesvirus 6A U4 Inhibits Proteasomal Degradation of the Amyloid Precursor Protein.

Human herpesvirus 6 (HHV-6) belongs to the betaherpesvirus subfamily and is divided into two distinct species, HHV-6A and HHV-6B. HHV-6 can infect nerve cells and is associated with a variety of nervous system diseases. Recently, the association of HHV-6A infection with Alzheimer's disease (AD) has been suggested. The main pathological phenomena of AD are the accumulation of ß-amyloid (Aß), neurofibrillary tangles, and neuroinflammation; however, the specific molecular mechanism of pathogenesis of AD is not completely clear. In this study, we focused on the effect of HHV-6A U4 gene function on Aß expression. Coexpression of HHV-6A U4 with amyloid precursor protein (APP) resulted in inhibition of ubiquitin-mediated proteasomal degradation of APP. Consequently, accumulation of ß-amyloid peptide (Aß), insoluble neurofibrillary tangles, and loss of neural cells may occur. Immunoprecipitation coupled with mass spectrometry (IP-MS) showed that HHV-6A U4 protein interacts with E3 ubiquitin ligase composed of DDB1 and cullin 4B, which is also responsible for APP degradation. We hypothesize that HHV-6A U4 protein competes with APP for binding to E3 ubiquitin ligase, resulting in the inhibition of APP ubiquitin modification and clearance. Finally, this leads to an increase in APP expression and Aß deposition, which are the hallmarks of AD. These findings provide novel evidence for the etiological hypothesis of AD, which can contribute to the further analysis of the role of HHV-6A in AD. IMPORTANCE The association of HHV-6A infection with Alzheimer's disease has attracted increasing attention, although its role and molecular mechanism remain to be established. Our results here indicate that HHV-6A U4 inhibits amyloid precursor protein (APP) degradation. U4 protein interacts with CRLs (cullin-RING E3 ubiquitin-protein ligases), which is also responsible for APP degradation. We propose a model in which U4 competitively binds to CRLs with APP, resulting in APP accumulation and Aß generation. Our findings provide new insights into the etiological hypothesis of HHV-6A in AD that can help further analyses.

Engineering propionyl-CoA pools for de novo biosynthesis of odd-chain fatty acids in microbial cell factories.

Odd-chain fatty acids (OcFAs) and their derivatives have attracted great interest due to their wide applications in the food, pharmaceutical and petrochemical industries. Microorganisms can naturally de novo produce fatty acids (FAs), where mainly, even-chain with acetyl-CoA instead of odd-chain with propionyl-CoA is used as the primer. Usually, the absence of the precursor propionyl-CoA is considered the main reason that limits the efficient production of OcFAs. It is thus crucial to explore/evaluate/identify promising propionyl-CoA biosynthetic pathways to achieve large-scale biosynthesis of OcFAs. This review discusses the latest advances in microbial metabolism engineering toward producing propionyl-CoA and considers future research directions and challenges toward optimized production of OcFAs.