Multiple Protein Interactions Research Articles

Characterisation and evolution of the PRC2 complex and its functional analysis under various stress conditions in rice

The polycomb repressive complex 2 (PRC2) is a chromatin-associated methyltransferase responsible for catalysing the trimethylation of H3K27, an inhibitory chromatin marker associated with gene silencing. This enzymatic activity is crucial for normal organismal development and the maintenance of gene expression patterns that preserve cellular identity, subsequently influencing plant growth and abiotic stress responses. Therefore, in this study, we investigated the evolutionary characteristics and functional roles of PRC2 in plants. We identified 209 PRC2 genes, including E(z), Su(z), Esc, and Nurf55 families, using 18 representative plant species and revealed that recent gene replication events have led to an expansion in the Nurf55 family, resulting in a greater number of members compared to the E(z), Su(z), and Esc families. Furthermore, protein structure and motif composition analyses highlighted the potential functional site regions within PRC2 members. In addition, we selected rice, a representative monocotyledonous plant, as the model species for food crops. Our findings revealed that SDG711, SDG718, and MSI1-5 genes were induced by abscisic acid (ABA) and/or methyl jasmonate (MeJA) hormones, suggesting that these genes play an important role in abiotic stress and disease resistance. Further experiments involving rice blast fungus treatments confirmed that the expression of SDG711 and MSI1-5 was induced by Magnaporthe oryzae strain GUY11. Multiple protein interaction assays revealed that the M. oryzae effector AvrPiz-t interacts with PRC2 core member SDG711 to increase H3K27me3 levels. Notably, inhibition of PRC2 or mutation of SDG711 enhanced rice resistance to M. oryzae. Collectively, these results provide new insights into PRC2 evolution in plants and its significant functions in rice.

Proximity labeling reveals dynamic changes in the SQSTM1 protein network

Sequestosome1 (SQSTM1) is an autophagy receptor that mediates the degradation of intracellular cargo, including protein aggregates, through multiple protein interactions. These interactions form the SQSTM1 protein network, and these interactions are mediated by SQSTM1 functional interaction domains, which include LIR, PB1, UBA, and KIR. Technological advances in cell biology continue to expand our knowledge of the SQSTM1 protein network and the relationship between the actions of the SQSTM1 protein network in cellular physiology and disease states. Here we apply proximity profile labeling to investigate the SQSTM1 protein interaction network by fusing TurboID with the human protein SQSTM1 (TurboID::SQSTM1). This chimeric protein displayed well-established SQSTM1 features including production of SQSTM1 intracellular bodies, binding to known SQSTM1 interacting partners, and capture of novel SQSTM1 protein interactors. Strikingly, aggregated tau protein altered the protein interaction network of SQSTM1 to include many stress-associated proteins. We demonstrate the importance of the PB1 and/or UBA domains for binding network members, including the K18 domain of tau. Overall, our work reveals the dynamic landscape of the SQSTM1 protein network and offers a resource to study SQSTM1 function in cellular physiology and disease state.

Understanding Longevity: SIN-3 and DAF-16 Revealed as Independent Players in Lifespan Regulation.

Aging is the process of gradual physio-biochemical deterioration. Although aging is inevitable, healthy aging is the key to individual and communal well-being. Therefore, it is essential to understand the regulation of aging. SIN-3/Sin-3 is a unique regulatory protein that regulates aging without DNA-binding activity. It functions by establishing multiple protein interactions. To understand the functional mechanism of this transcriptional regulator, the Caenorhabditis elegans protein interactome was assessed for SIN-3 interactions. DAF-16/FOXO emerged as one of the leading contenders for SIN-3-mediated regulation of aging. This study looks at the concerted role of SIN-3 and DAF-16 proteins in lifespan regulation. Phenotypic profiling for the mutants of these genes shows the functional accord between these 2 proteins with similar functions in stress response and vital biological processes. However, there were no significant physical interactions when checked for protein-protein interaction between SIN-3 and DAF-16 proteins. C. elegans genomics and transcriptomics data also indicated the possibilities of concerted gene regulation. This genetic regulation is more likely related to SIN-3 dominance on DAF-16 function. Overall, SIN-3 and DAF-16 proteins have strong functional interactions that ensure healthy aging. The influence of SIN-3 on DAF-16-mediated stress response is one of their convergence points in longevity regulation.

Computational Insights into Captopril's Inhibitory Potential Against MMP9 and LCN2 in Bladder Cancer: Implications for Therapeutic Application.

Captopril is a commonly used therapeutic agent in the management of renovascular hypertension (high blood pressure), congestive heart failure, left ventricular dysfunction following myocardial infarction, and nephropathy. Captopril has been found to interact with proteins that are significantly associated with bladder cancer (BLCA), suggesting that it could be a potential medication for BLCA patients with concurrent hypertension. DrugBank 5.0 was utilized to identify the direct protein targets (DPTs) of captopril. STRING was used to analyze the multiple protein interactions. TNMPlot was used for comparing gene expression in normal, tumor, and metastatic tissue. Then, docking with target proteins was done using Autodock. Molecular dynamics simulations were applied for estimate the diffusion coefficients and mean-square displacements in materials. Among all these proteins, MMP9 is observed to be an overexpressed gene in BLCA and its increased expression is linked to reduced survival in patients. Our findings indicate that captopril effectively inhibits both the wild type and common mutated forms of MMP9 in BLCA. Furthermore, the LCN2 gene, which is also overexpressed in BLCA, interacts with captopril-associated proteins. The overexpression of LCN2 is similarly associated with reduced survival in BLCA. Through molecular docking analysis, we have identified specific amino acid residues (Tyr179, Pro421, Tyr423, and Lys603) at the active pocket of MMP9, as well as Tyr78, Tyr106, Phe145, Lys147, and Lys156 at the active pocket of LCN2, with which captopril interacts. Thus, our data provide compelling evidence for the inhibitory potential of captopril against human proteins MMP9 and LCN2, both of which play crucial roles in BLCA. These discoveries present promising prospects for conducting subsequent validation studies both in vitro and in vivo, with the aim of assessing the suitability of captopril for treating BLCA patients, irrespective of their hypertension status, who exhibit elevated levels of MMP9 and LCN2 expression.

Heat stress impairs floral meristem termination and fruit development by affecting the BR-SlCRCa cascade in tomato

Floral meristem termination is a key step leading to carpel initiation and fruit development. The frequent occurrence of heat stress due to global warming often disrupts floral determinacy, resulting in defective fruit formation. However, the detailed mechanism behind this phenomenon is largely unknown. Here, we identify CRABS CLAW a (SlCRCa) as a key regulator of floral meristem termination in tomato. SlCRCa functions as an indispensable floral meristem terminator by suppressing SlWUS activity through the TOMATO AGAMOUS 1 (TAG1)–KNUCKLES (SlKNU)–INHIBITOR OF MERISTEM ACTIVITY (SlIMA) network. A direct binding assay revealed that SlCRCa specifically binds to the promoter and second intron of WUSCHEL (SlWUS). We also demonstrate that SlCRCa expression depends on brassinosteroid homeostasis in the floral meristem, which is repressed by heat stress via the circadian factor EARLY FLOWERING 3 (SlELF3). These results provide new insights into floral meristem termination and the heat stress response in flowers and fruits of tomato and suggest that SlCRCa provides a platform for multiple protein interactions that may epigenetically abrogate stem cell activity at the transition from floral meristem to carpel initiation.

Identification of fragments targeting SMYD3 using highly sensitive kinetic and multiplexed biosensor-based screening.

A 1056-membered fragment library has been screened against SMYD3 using a novel multiplexed experimental design implemented in a grating coupled interferometry (GCI)-based biosensor. SMYD3 is a prospective target for anticancer drugs and the focus has initially been on discovery of inhibitors of its lysine methyl transferase activity. However, it has multiple protein interaction partners and several potential roles in carcinogenesis. It therefore remains unclear what mode of action ligands targeting the protein should have. Our goal was therefore to identify new ligands and discriminate hits that interact with the active site and those that interact with other sites. In addition, we were interested in selecting hits based on kinetic features rather than affinity. Screening was done in parallel against SMYD3 alone or SMYD3 with the active site blocked by a tight binding inhibitor. Hit selection was primarily based on dissociation rates. In total, 20 fragments were selected as hits, of which half apparently targeted the active site and half targeted other sites. Twelve of the hits were selected for structural analysis using X-ray crystallography in order to identify binding sites and modes of binding. Four of the hits were successfully identified in crystal structures with SMYD3; the others did not show any electron densities for ligands in the crystals. Although it might be possible to optimize the crystallography approach for a better success rate, it was clear that the sensitivity and time resolution of the biosensor assay was exceptional and enabled kinetic rate constants to be estimated for fragments. Fragments are typically considered to interact too rapidly for such quantification to be possible. This approach consequently represents a paradigm shift. In addition, the multiplexed approach allows ligands targeting different sites to be rationally selected already in the fragment library screening stage.

Heteroprotein complex coacervation of ovalbumin and lysozyme: Phase behavior, microstructure and processing properties

Egg white protein is a complex network system formed by the aggregation and interaction of multiple proteins, in which two oppositely charged proteins can induce the formation of heteroprotein complex coacervate (HPCC). This investigation aims to probe the complexation between ovalbumin (OVA) and lysozyme (LYS) via the heteroproteins phase diagram model, exploring the relationship between differential processing properties and complex state, protein molecular structure and intermolecular interactions. Results showed that the characteristic pH (pHc, pHɸ1, pHmax, pHɸ2) intensely relied on the protein ratios. Consequences of ζ-potential and the phase diagram manifested that OVA-LYS complex formation was predominantly triggered by electrostatic interactions. With the increasing OVA-LYS mixing ratio, the characteristic pH of the complex moved towards a higher pH value. By comparing the microphase structure of different phase regions induced by pH, we found that the protein structure unfolded at low pH, elevating the foaming and emulsifying capacity. Moreover, further increases in pH value brought on larger insoluble complex formation, which enhanced the foaming stability while decreased the emulsifying stability. Noteworthy, the coacervates obtained in the narrow range of pH 6.5–9.5 presented the strongest gel strength and highest water holding capacity, which was considered to be an efficacious way to regulate the gel properties of egg white protein. On the whole, the findings of this paper developed prominent insight for understanding the interaction between heteroproteins, which would lay a theoretical foundation for improving the quality and efficiency of functional egg powder and product development.

Proteomic analysis of 'Korla' fragrant pear responsed during early infection of Alternaria alternata

‘Korla’ fragrant pears are highly prone to Alternaria alternata (A. alternata) infection. Herein we performed isobaric tags for relative and absolute quantitation (iTRAQ)-based comparative proteomic analysis to evaluate the response of ‘Korla’ fragrant pears to A. alternata invasion at different timepoints (0 h, 24 h, 72 h, and 120 h). Our analyses led to the identification of 939 differentially abundant proteins. Protein function annotation and enrichment analysis indicated that in response to A. alternata infection, ‘Korla’ fragrant pear strongly activates defense-related proteins and activates signaling mechanism, further accelerates the phenylpropane metabolic pathway, and modifies the cell wall through redox related proteins and hormone signaling molecules, thus expressing the interaction of multiple defense related proteins involved in a series of biochemical reactions to form a Pathogen-related defense proteins. Our findings enhance our understanding of the interaction mechanism between plants and pathogens.

Label-Free Multiplexed Microfluidic Analysis of Protein Interactions Based on Photonic Crystal Surface Mode Imaging.

High-throughput protein assays are crucial for modern diagnostics, drug discovery, proteomics, and other fields of biology and medicine. It allows simultaneous detection of hundreds of analytes and miniaturization of both fabrication and analytical procedures. Photonic crystal surface mode (PC SM) imaging is an effective alternative to surface plasmon resonance (SPR) imaging used in conventional gold-coated, label-free biosensors. PC SM imaging is advantageous as a quick, label-free, and reproducible technique for multiplexed analysis of biomolecular interactions. PC SM sensors are characterized by a longer signal propagation at the cost of a lower spatial resolution, which makes them more sensitive than classical SPR imaging sensors. We describe an approach for designing label-free protein biosensing assays employing PC SM imaging in the microfluidic mode. Label-free, real-time detection of PC SM imaging biosensors using two-dimensional imaging of binding events has been designed to study arrays of model proteins (antibodies, immunoglobulin G-binding proteins, serum proteins, and DNA repair proteins) at 96 points prepared by automated spotting. The data prove feasibility of simultaneous PC SM imaging of multiple protein interactions. The results pave the way to further develop PC SM imaging as an advanced label-free microfluidic assay for the multiplexed detection of protein interactions.

ApoE4 associated with severe COVID-19 outcomes via downregulation of ACE2 and imbalanced RAS pathway

BackgroundRecent numerous epidemiology and clinical association studies reported that ApoE polymorphism might be associated with the risk and severity of coronavirus disease 2019 (COVID-19), and yielded inconsistent results. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection relies on its spike protein binding to angiotensin-converting enzyme 2 (ACE2) receptor expressed on host cell membranes.MethodsA meta-analysis was conducted to clarify the association between ApoE polymorphism and the risk and severity of COVID-19. Multiple protein interaction assays were utilized to investigate the potential molecular link between ApoE and the SARS-CoV-2 primary receptor ACE2, ApoE and spike protein. Immunoblotting and immunofluorescence staining methods were used to access the regulatory effect of different ApoE isoform on ACE2 protein expression.ResultsApoE gene polymorphism (ε4 carrier genotypes VS non-ε4 carrier genotypes) is associated with the increased risk (P = 0.0003, OR = 1.44, 95% CI 1.18–1.76) and progression (P < 0.00001, OR = 1.85, 95% CI 1.50–2.28) of COVID-19. ApoE interacts with both ACE2 and the spike protein but did not show isoform-dependent binding effects. ApoE4 significantly downregulates ACE2 protein expression in vitro and in vivo and subsequently decreases the conversion of Ang II to Ang 1–7.ConclusionsApoE4 increases SARS-CoV-2 infectivity in a manner that may not depend on differential interactions with the spike protein or ACE2. Instead, ApoE4 downregulates ACE2 protein expression and subsequently the dysregulation of renin–angiotensin system (RAS) may provide explanation by which ApoE4 exacerbates COVID-19 disease.

Towards a structurally resolved human protein interaction network

Cellular functions are governed by molecular machines that assemble through protein-protein interactions. Their atomic details are critical to studying their molecular mechanisms. However, fewer than 5% of hundreds of thousands of human protein interactions have been structurally characterized. Here we test the potential and limitations of recent progress in deep-learning methods using AlphaFold2 to predict structures for 65,484 human protein interactions. We show that experiments can orthogonally confirm higher-confidence models. We identify 3,137 high-confidence models, of which 1,371 have no homology to a known structure. We identify interface residues harboring disease mutations, suggesting potential mechanisms for pathogenic variants. Groups of interface phosphorylation sites show patterns of co-regulation across conditions, suggestive of coordinated tuning of multiple protein interactions as signaling responses. Finally, we provide examples of how the predicted binary complexes can be used to build larger assemblies helping to expand our understanding of human cell biology.

Dynamic Enrichment for Evaluation of Protein Networks (DEEPN): A High Throughput Yeast Two-Hybrid (Y2H) Protocol to Evaluate Networks.

Proteins are the building blocks of life, and a vast array of cellular processes is handled by protein-protein interactions (PPIs). The protein complexes formed via PPIs lead to tangled networks that, with their continuous remodeling, build up systematic functional units. Over the years, PPIs have become an area of interest for many researchers, leading to the development of multiple in vitro and in vivo methods to reveal these interactions. The yeast-two-hybrid (Y2H) system is a potent genetic way to map PPIs in both a micro- and high-throughput manner. Y2H is a technique that involves using modified yeast cells to identify protein-protein interactions. For Y2H, the yeast cells are engineered only to grow when there is a significant interaction between a specific protein with its interacting partner. PPIs are identified in the Y2H system by stimulating reporter genes in response to a restored transcription factor. However, Y2H results may be constrained by stringency requirements, as the limited number of colony screenings through this technique could result in the possible elimination of numerous genuine interactions. Therefore, DEEPN (dynamic enrichment for evaluation of protein networks) can be used, offering the potential to study the multiple static and transient protein interactions in a single Y2H experiment. DEEPN utilizes next-generation DNA sequencing (NGS) data in a high-throughput manner and subsequently applies computational analysis and statistical modeling to identify interacting partners. This protocol describes customized reagents and protocols through which DEEPN analysis can be utilized efficiently and cost-effectively.

PS-B12-11: FUNCTIONAL VERSATILITY OF (PRO) RENIN RECEPTOR CLARIFIED BY STRUCTURAL AND EVOLUTIONARY ANALYSES

Objective: (Pro)renin receptor [(P)RR] is a single-span membrane protein originally identified as a regulator of the renin-angiotensin-aldosterone system. (P)RR reportedly exerts various functions, including an accessory protein of vacuolar ATPase complex and a component of Wnt receptor complex. The soluble form of (P)RR [s(P)RR] which comprises of most of extracellular domain (ECD) exerts an antidiuretic action. although the versatile functions should be mediated through the interactions between (p)rr ecd and its respective binding partners, the one-to-many bindings has not been fully explained. Here we investigated the binding mode of this receptor by structural and evolutionary analyses using three-dimensional structural models of (P)RR, which were predicted by the AlphaFold2 (AF2) program, a machine learning-based algorithm capable of predicting protein structure to near experimental accuracy. Design and method: Monoclonal antibodies against (P)RR reduce the Wnt/beta-catenin-dependent development of pancreatic ductal adenocarcinoma (PDAC), the most common pancreatic cancer. Antibodies against two (P)RR regions (residues 47–60 and 200–213) located in ECD reduce the proliferation of human PDAC cells in vitro. The spatial distribution of the two regions was examined using human (P)RR AF2 structural models (monomer and dimer). The evolutionary conservation profile and hydrophobicity were mapped on the models. Results: The dimer structure predicted by AF2 shows that (P)RR homodimerizes via ECD, which explains the experimentally proven dimer formation. The 47–60 and 200–213 regions of (P)RR formed a continuous surface patch on the structural model, which comprised evolutionarily conserved hydrophobic residues. The dimer model revealed the presence of two hand-like grooves, with 47–60 and 200–213 regions as its palm and 270–296 region (intrinsically disordered region, IDR) as its fingers. Conclusions: Considering conformational flexibility of IDR allowing for multiple protein interactions, we propose that the grooves may act as a binding interface with Wnt signaling molecules and antibodies against the grooves probably interfere with the formation of Wnt receptor complex due to steric hindrance and direct competition with the binding interface residues. The hydrophobic nature of the grooves may explain why (P)RR shows one-to-many bindings underpinning its functional versatility. This study provides new insights into the binding mode of (P)RR for the first time. s(P)RR is considered a useful biomarker for diseases, including essential hypertension and cancer. Our findings may help explore a new treatment and biomarker testing of human diseases, and contribute to quality of life in a longevity society.

Drought Stress-Related Gene Identification in Rice by Random Walk with Restart on Multiplex Biological Networks

Drought stress-related gene identification is vital in revealing the drought resistance mechanisms underlying rice and for cultivating rice-resistant varieties. Traditional methods, such as Genome-Wide Association Studies (GWAS), usually identify hundreds of candidate stress genes, and further validation by biological experiements is then time-consuming and laborious. However, computational and prioritization methods can effectively reduce the number of candidate stress genes. This study introduces a random walk with restart algorithm (RWR), a state-of-the-art guilt-by-association method, to operate on rice multiplex biological networks. It explores the physical and functional interactions between biological molecules at different levels and prioritizes a set of potential genes. Firstly, we integrated a Protein–Protein Interaction (PPI) network, constructed by multiple protein interaction data, with a gene coexpression network into a multiplex network. Then, we implemented the RWR on multiplex networks (RWR-M) with known drought stress genes as seed nodes to identify potential drought stress-related genes. Finally, we conducted association analysis between the potential genes and the known drought stress genes. Thirteen genes were identified as rice drought stress-related genes, five of which have been reported in the recent literature to be involved in drought stress resistance mechanisms.

Mapping the protein binding site of the (pro)renin receptor using in silico 3D structural analysis

We have previously reported that monoclonal antibodies against the (pro)renin receptor [(P)RR] can reduce the Wnt/β-catenin-dependent development of pancreatic ductal adenocarcinoma (PDAC), the most common pancreatic cancer. Antibodies against two (P)RR regions (residues 47–60 and 200–213) located in the extracellular domain (ECD) reduced the proliferation of human PDAC cells in vitro. Although these regions probably participate in the activation of Wnt/β-catenin signaling, their functional significance remains unclear. Moreover, the (P)RR ECD is predicted to possess an intrinsically disordered region (IDR), which allows multiple protein interactions because of its conformational flexibility. In this study, we investigated the significance of the two regions and the IDR by in silico 3D structural analysis using the AlphaFold2 program and evolutionary sequence conservation profile. The model showed that ECD adopted a folded domain (residues 17–269) and had an IDR (residues 270–296). The two regions mapped onto the structural model formed a continuous surface patch comprising evolutionarily conserved hydrophobic residues. The homodimeric structure predicted by AlphaFold2 showed that full-length (P)RR comprising the ECD, single-span transmembrane, and cytoplasmic domains formed a twofold symmetric dimer via the ECD, which explains the experimentally proven homodimerization. The dimer model possessed two hand-shaped grooves with residues 47–60 and 200–213 in their palms and the IDR as their fingers. Based on these findings, we propose that the IDR-containing hydrophobic grooves act as a binding site for (P)RR and perform multiple functions, including Wnt signaling activation.Antibodies against the (pro)renin receptor residues 47–60 and 200–213 can inhibit pancreatic ductal adenocarcinoma (PDAC) cell proliferation by suppressing Wnt signaling. This study provides 3D structural insights into receptor binding and one-to-many interactions, which underpin the functional versatility of this receptor.

Deficient Sarcolemma Repair in ALS: A Novel Mechanism with Therapeutic Potential.

The plasma membrane (sarcolemma) of skeletal muscle myofibers is susceptible to injury caused by physical and chemical stresses during normal daily movement and/or under disease conditions. These acute plasma membrane disruptions are normally compensated by an intrinsic membrane resealing process involving interactions of multiple intracellular proteins including dysferlin, annexin, caveolin, and Mitsugumin 53 (MG53)/TRIM72. There is new evidence for compromised muscle sarcolemma repair mechanisms in Amyotrophic Lateral Sclerosis (ALS). Mitochondrial dysfunction in proximity to neuromuscular junctions (NMJs) increases oxidative stress, triggering MG53 aggregation and loss of its function. Compromised membrane repair further worsens sarcolemma fragility and amplifies oxidative stress in a vicious cycle. This article is to review existing literature supporting the concept that ALS is a disease of oxidative-stress induced disruption of muscle membrane repair that compromise the integrity of the NMJs and hence augmenting muscle membrane repair mechanisms could represent a viable therapeutic strategy for ALS.

Transcriptome profiling combined with network analysis deepens the understanding of immune response mechanisms in blood of pacific oyster Crassostrea gigas infected by Vibrio alginolyticus

Mass mortalities of oysters during the summer have been reported for years. Among the biological factors causing oyster death in summer, Vibrio infection is considered to be the most important factor. Vibrio alginolyticus is one of the main pathogens causing oyster diseases. V. alginolyticus can cause disease and death of fish, shrimp, shellfish, and other aquatic products. Human infection with V. alginolyticus can also cause skin infections, external ear canal infections, and other diseases. Hemocytes in the blood of Crassostrea gigas resemble vertebrate macrophages and play an important role in the immune regulation of organisms. Therefore, it is of great significance to analyze the blood transcriptome to study the anti-pathogen mechanism of the C. gigas. In our study, we performed a transcriptome profile of gene expression on C. gigas infected with V. alginolyticus at 12 and 48 hours, and identified 2,494 and 1,165 differentially expressed genes (DEGs) at two sampling time points. Then, the functions of DEGs were identified using GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) functional enrichment analysis, revealing that there were multiple significantly enriched GO terms and KEGG signaling pathways related to immunity. And a protein-protein interaction (PPI) network was construct using DEGs enriched in significant enriched immune-related KEGG signaling pathways. At last, we screened and validated 12 key genes with multiple protein interaction numbers or involved in more KEGG signaling pathways, and verified their expression changes by quantitative RT-PCR (qRT-PCR). For the first time, we studied the immune defense mechanism of C. gigas blood based on protein-protein interaction network, which explains how C. gigas lacking specific immunity survive in a pathogen-rich environment. This research provides reference for solving the problem of high mortality of C. gigas and other mollusks in summer, and provides reference for the future production of some disease-resistant C. gigas.

APOE interacts with ACE2 inhibiting SARS-CoV-2 cellular entry and inflammation in COVID-19 patients

Apolipoprotein E (APOE) plays a pivotal role in lipid including cholesterol metabolism. The APOE ε4 (APOE4) allele is a major genetic risk factor for Alzheimer’s and cardiovascular diseases. Although APOE has recently been associated with increased susceptibility to infections of several viruses, whether and how APOE and its isoforms affect SARS-CoV-2 infection remains unclear. Here, we show that serum concentrations of APOE correlate inversely with levels of cytokine/chemokine in 73 COVID-19 patients. Utilizing multiple protein interaction assays, we demonstrate that APOE3 and APOE4 interact with the SARS-CoV-2 receptor ACE2; and APOE/ACE2 interactions require zinc metallopeptidase domain of ACE2, a key docking site for SARS-CoV-2 Spike protein. In addition, immuno-imaging assays using confocal, super-resolution, and transmission electron microscopies reveal that both APOE3 and APOE4 reduce ACE2/Spike-mediated viral entry into cells. Interestingly, while having a comparable binding affinity to ACE2, APOE4 inhibits viral entry to a lesser extent compared to APOE3, which is likely due to APOE4’s more compact structure and smaller spatial obstacle to compete against Spike binding to ACE2. Furthermore, APOE ε4 carriers clinically correlate with increased SARS-CoV-2 infection and elevated serum inflammatory factors in 142 COVID-19 patients assessed. Our study suggests a regulatory mechanism underlying SARS-CoV-2 infection through APOE interactions with ACE2, which may explain in part increased COVID-19 infection and disease severity in APOE ε4 carriers.

Fused in Liposarcoma Protein, a New Player in the Regulation of HIV-1 Transcription, Binds to Known and Newly Identified LTR G-Quadruplexes.

HIV-1 integrated long terminal repeat (LTR) promoter activity is modulated by folding of its G-rich region into non-canonical nucleic acids structures, such as G-quadruplexes (G4s), and their interaction with cellular proteins. Here, by a combined pull-down/mass spectrometry/Western-blot approach, we identified the fused in liposarcoma (FUS) protein and found it to preferentially bind and stabilize the least stable and bulged LTR G4, especially in the cell environment. The outcome of this interaction is the down-regulation of viral transcription, as assessed in a reporter assay with LTR G4 mutants in FUS-silencing conditions. These data indicate that the complexity and dynamics of HIV-1 LTR G4s are much greater than previously envisaged. The G-rich LTR region, with its diverse G4 landscape and multiple cell protein interactions, stands out as prime sensing center for the fine regulation of viral transcription. This region thus represents a rational antiviral target for inhibiting both the actively transcribing and latent viruses.

Purification of the human cone‐rod homeobox protein

A “lock and key” is the most common depiction of protein binding, protein has a specific structure, and its binding molecule of interest can fit into it. What happens when a protein domain needs to bind to multiple biomolecules? The transcription factor CRX is one of those with an activation domain that can bind to various biomolecules. CRX regulates the gene expression of cone and rod photoreceptors. To effectively regulate gene expression, CRX’s activation domain interacts with multiple transcriptional co‐activators. Unlike the “lock and key” concept with defined structures, we propose that the activation domain of CRX is intrinsically disordered, allowing for interactions of multiple proteins in the same domain. In support of a disordered activation domain, we observe that proline and serine amino acids are abundant in the CRX activation domain. We also note an abundance of pathogenic frameshift mutations and a lack of point mutants in the activation domain. To characterize the structure of CRX, we attempted to purify full‐length CRX and CRX coexpressed with known transcriptional coactivator NRL. We hypothesize that this latter experiment will enhance the stability and expression of full‐length CRX. We have purified CRX using nickel chromatography and are currently optimizing the next steps to enhance the purity of CRX and NRL. The information from biochemical and structural experiments on purified CRX will provide insight into the transcriptional regulation of CRX, leading to the development of photoreceptor neurons.