mBio最新文献

{"title":"Neutralization and spike stability of JN.1-derived LB.1, KP.2.3, KP.3, and KP.3.1.1 subvariants.","authors":"Pei Li, Julia N Faraone, Cheng Chih Hsu, Michelle Chamblee, Yajie Liu, Yi-Min Zheng, Yan Xu, Claire Carlin, Jeffrey C Horowitz, Rama K Mallampalli, Linda J Saif, Eugene M Oltz, Daniel Jones, Jianrong Li, Richard J Gumina, Joseph S Bednash, Kai Xu, Shan-Lu Liu","doi":"10.1128/mbio.00464-25","DOIUrl":"10.1128/mbio.00464-25","url":null,"abstract":"<p><p>During the summer of 2024, coronavirus disease 2019 (COVID-19) cases surged globally, driven by variants derived from JN.1 subvariants of severe acute respiratory syndrome coronavirus 2 that feature new mutations, particularly in the N-terminal domain (NTD) of the spike protein. In this study, we report on the neutralizing antibody (nAb) escape, infectivity, fusion, and spike stability of these subvariants-LB.1, KP.2.3, KP.3, and KP.3.1.1. Our findings demonstrate that all of these subvariants are highly evasive of nAbs elicited by the bivalent mRNA vaccine, the XBB.1.5 monovalent mumps virus-based vaccine, or from infections during the BA.2.86/JN.1 wave. This reduction in nAb titers is primarily driven by a single serine deletion (DelS31) in the NTD of the spike, leading to a distinct antigenic profile compared to the parental JN.1 and other variants. We also found that the DelS31 mutation decreases pseudovirus infectivity in CaLu-3 cells, which correlates with impaired cell-cell fusion. Additionally, the spike protein of DelS31 variants appears more conformationally stable, as indicated by reduced S1 shedding both with and without stimulation by soluble ACE2 and increased resistance to elevated temperatures. Molecular modeling suggests that DelS31 enhances the NTD-receptor-binding domain (RBD) interaction, favoring the RBD down conformation and reducing accessibility to ACE2 and specific nAbs. Moreover, DelS31 introduces an N-linked glycan at N30, shielding the NTD from antibody recognition. These findings underscore the role of NTD mutations in immune evasion, spike stability, and viral infectivity, highlighting the need to consider DelS31-containing antigens in updated COVID-19 vaccines.IMPORTANCEThe emergence of novel severe acute respiratory syndrome coronavirus 2 variants continues to pose challenges for global public health, particularly in the context of immune evasion and viral stability. This study identifies a key N-terminal domain (NTD) mutation, DelS31, in JN.1-derived subvariants that enhances neutralizing antibody escape while reducing infectivity and cell-cell fusion. The DelS31 mutation stabilizes the spike protein conformation, limits S1 shedding, and increases thermal resistance, which possibly contribute to prolonged viral persistence. Structural analyses reveal that DelS31 enhances NTD-receptor-binding domain interactions by introducing glycan shielding, thus decreasing antibody and ACE2 accessibility. These findings emphasize the critical role of NTD mutations in shaping viral evolution and immune evasion, underscoring the urgent need for updated coronavirus disease 2019 vaccines that account for these adaptive changes.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0046425"},"PeriodicalIF":5.1,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12077133/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143710607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"<i>IFITM3</i> variants point to a critical role in emergent virus infections.","authors":"Parker J Denz, Jacob S Yount","doi":"10.1128/mbio.03347-24","DOIUrl":"10.1128/mbio.03347-24","url":null,"abstract":"<p><p>Interferon-induced transmembrane protein 3 (IFITM3) is a cellular protein that restricts numerous viral infections by blocking virus-host membrane fusion. In humans, there are two <i>IFITM3</i> single nucleotide polymorphisms (SNPs), rs12252-C and rs34481144-A, that decrease IFITM3 activity and have been associated with severe illness following influenza virus infections. Mice lacking IFITM3 show increased influenza severity, supporting this association. However, some studies do not find a consistent link between <i>IFITM3</i> SNPs and infection severity, causing uncertainty about its role <i>in vivo</i>. Review of the literature indicates that <i>IFITM3</i> SNPs are primarily associated with increased viral disease in infections with emergent influenza viruses, such as the 2009 H1N1 pandemic virus and zoonotic H7N9 virus. Similarly, <i>IFITM3</i> SNPs are reported to be risk factors for increased severity in other emergent infections, including SARS-CoV-2, Hantaan virus, and HIV. In contrast, most studies that failed to find an association examined seasonal influenza. We posit that adaptive immune mechanisms, including pre-existing antibodies and memory T cells against seasonally circulating viruses, compensate for IFITM3 deficiencies, therefore masking its role in seasonal influenza. We propose that IFITM3 is most critical in defending against emergent viruses and should be a key focus of public health strategies to prevent the emergence and spread of novel pathogens, with individuals carrying <i>IFITM3</i> SNPs potentially benefiting from broadened vaccine coverage, avoidance of animal reservoirs, or enhanced masking to protect themselves and the wider population.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":"16 5","pages":"e0334724"},"PeriodicalIF":5.1,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12077130/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143971276","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characterization of proteins present in the biofilm matrix and outer membrane vesicles of <i>Histophilus somni</i> during iron-sufficient and iron-restricted growth: identification of potential protective antigens through <i>in silico</i> analyses.","authors":"Yue-Jia Lee, Mohd Abdullah, Yung-Fu Chang, Habeeb Al Sudani, Thomas J Inzana","doi":"10.1128/mbio.00644-25","DOIUrl":"10.1128/mbio.00644-25","url":null,"abstract":"<p><p>There is limited efficacy in vaccines currently available to prevent some animal diseases of bacterial origin, such as bovine respiratory disease caused by <i>Histophilus somni</i>. Protective efficacy can potentially be improved if bacterial antigens that are expressed in the host are included in vaccines. During <i>H. somni</i> infection in the bovine host, biofilms become established, and the availability of essential iron is restricted. To investigate further, the protein composition of spontaneously released outer membrane vesicles (OMVs) during iron-sufficient and iron-restricted growth and the proteins expressed in the biofilm matrix were analyzed and compared. Proteomic analysis revealed a dramatic physiological change in <i>H. somni</i> as it transitioned from the planktonic form to the biofilm mode of growth. All transferrin-binding proteins (Tbps) previously identified in <i>H. somni</i> were detected in the OMVs, suggesting that OMVs could induce antibodies to these proteins. Two TbpA-like proteins and seven total proteins were present in the OMVs only when iron was restricted, indicating the expression of these Tbps was differentially regulated. More proteins associated with quorum-sensing (QS) signaling were detected in the biofilm matrix compared with proteins in the OMVs, supporting a link between QS and biofilm formation. Proteins ACA31267.1 (OmpA) and ACA32419.1 (TonB-dependent receptor) were present in the OMV and biofilm matrix and predicted to be potential protective antigens using an immuno-bioinformatic approach. Overall, the results support the development of novel vaccines that contain OMVs obtained from bacteria grown to simulate the <i>in vivo</i> environment, and possibly biofilm matrix, to prevent diseases caused by bacterial pathogens.IMPORTANCEBovine respiratory disease (BRD) is the most economically important disease affecting the cattle industry. Available BRD vaccines consist of killed bacteria but are not very effective. Poor vaccine efficacy may be because the phenotype of bacteria in the host differs from the phenotype of cultured bacteria. Following host infection, virulent bacteria can express transferrin-binding proteins (Tbps) not expressed in culture medium but are required to sequester iron from host proteins. During chronic infections, such as BRD, bacteria can form a biofilm consisting of novel protein and polysaccharide antigens. The unique proteins expressed on outer membrane vesicles (OMVs) of <i>Histophilus somni</i> (a BRD pathogen) in the absence of iron and as a biofilm were identified and characterized. At least two TbpA-like proteins were expressed in OMVs only under iron-limiting conditions. Quorum-sensing-associated proteins were identified in the <i>H. somni</i> biofilm matrix. <i>In silico</i> analysis identified potential protein targets for vaccine development.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":"16 5","pages":"e0064425"},"PeriodicalIF":5.1,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12077179/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143991605","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"mGem: Sepsis and antimicrobial resistance in the context of advanced HIV disease.","authors":"Rachel M Wake, Nelesh P Govender","doi":"10.1128/mbio.00769-24","DOIUrl":"10.1128/mbio.00769-24","url":null,"abstract":"<p><p>Sepsis triggered by bloodstream infections (BSI) is a significant driver of HIV-related mortality, particularly among in-patients with advanced HIV disease (AHD). Currently, the incidence, etiology, and outcomes of BSI in this population are poorly defined. We review the existing evidence, which shows an increased risk of BSI, particularly with antimicrobial-resistant (AMR) organisms, and higher BSI-associated mortality in patients with AHD. Causative bacterial and fungal pathogens are often unknown, but when identified, limited data show etiology has shifted probably owing to increasing coverage of antiretroviral treatment, antimicrobial prophylaxis, and rising global AMR trends. Further research is crucial to design and refine interventions before, during, and after hospital admission to reduce sepsis-related mortality in patients with AHD.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":"16 5","pages":"e0076924"},"PeriodicalIF":5.1,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12077103/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144016305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Endoplasmic reticulum facilitates the coordinated division of <i>Salmonella</i>-containing vacuoles.","authors":"Umesh Chopra, Priyanka Bhansali, Subba Rao Gangi Setty, Dipshikha Chakravortty","doi":"10.1128/mbio.00114-25","DOIUrl":"10.1128/mbio.00114-25","url":null,"abstract":"<p><p><i>Salmonella</i> Typhimurium (STM) resides in a membrane-bound compartment called the <i>Salmonella</i>-containing vacuole (SCV) in several infected cell types where bacterial and SCV division occur synchronously to maintain a single bacterium per vacuole. However, the mechanism behind this synchronous fission is not well understood. Fission of intracellular organelles is known to be regulated by the dynamic tubular endoplasmic reticulum (ER). In this study, we evaluated the role of ER in controlling SCV division. Interestingly, <i>Salmonella</i>-infected cells show activation of the unfolded protein response (UPR) and expansion of ER tubules. Altering the expression of ER morphology regulators, such as reticulon-4a (Rtn4a) and CLIMP63, significantly impacted bacterial proliferation, suggesting a potential role of tubular ER in facilitating SCV division. Live-cell imaging revealed the marking of tubular ER at the center of 78% of SCV division sites. This study also explored the role of SteA (a known <i>Salmonella</i> effector in modulating membrane dynamics) in coordinating the SCV division. SteA resides on the SCV membranes and helps form membrane contact between SCV and ER. The colocalization of ER with SCV enclosing STMΔ<i>steA</i> was significantly reduced, compared with SCV of STM WT or STMΔ<i>steA:steA</i>. STMΔ<i>steA</i> shows profound defects in SCV division, resulting in multiple bacteria in a single vacuole with proliferation defects. <i>In vivo</i>, the STMΔ<i>steA</i> shows a defect in colonization in the spleen and liver and affects the initial survival rate of mice. Overall, this study suggests a coordinated role of bacterial effector SteA in promoting ER contact/association with SCVs and regulating SCV division.IMPORTANCEThis study highlights the essential role of the host endoplasmic reticulum in facilitating SCV division and maintaining a single bacterium per vacuole. The <i>Salmonella</i> effector SteA helps maintain the single bacterium per vacuole state. In the absence of SteA, <i>Salmonella</i> resides as multiple bacteria within a single large vacuole. The STMΔ<i>steA</i> shows reduced proliferation under <i>in vitro</i> conditions and exhibits colonization defects <i>in vivo</i>, highlighting the importance of this effector in <i>Salmonella</i> pathogenesis. These findings suggest that targeting SteA could provide a novel therapeutic approach to inhibit <i>Salmonella</i> pathogenicity.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":"16 5","pages":"e0011425"},"PeriodicalIF":5.1,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12077215/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144017792","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fructose activates a stress response shared by methylglyoxal and hydrogen peroxide in <i>Streptococcus mutans</i>.","authors":"Alejandro R Walker, Danniel N Pham, Payam Noeparvar, Alexandra M Peterson, Marissa K Lipp, José A Lemos, Lin Zeng","doi":"10.1128/mbio.00485-25","DOIUrl":"10.1128/mbio.00485-25","url":null,"abstract":"<p><p>Fructose catabolism by <i>Streptococcus mutans</i> is initiated by three phosphotransferase (PTS) transporters yielding fructose-1-phosphate (F-1-P) or fructose-6-phosphate. Deletion of one such F-1-P-generating PTS, <i>fruI</i>, was shown to reduce the cariogenicity of <i>S. mutans</i> in rats fed a high-sucrose diet. Moreover, a recent study linked fructose metabolism in <i>S. mutans</i> to a reactive electrophile species methylglyoxal. Here, we conducted a comparative transcriptomic analysis of <i>S. mutans</i> treated briefly with 50 mM fructose, 50 mM glucose, 5 mM methylglyoxal, or 0.5 mM hydrogen peroxide (H₂O₂). The results revealed a striking overlap between the fructose and methylglyoxal transcriptomes, totaling 176 genes, 61 of which were also shared with the H₂O₂ transcriptome. This core of 61 genes encompassed many of the same pathways affected by exposure to low pH or zinc intoxication. Consistent with these findings, fructose negatively impacted the metal homeostasis of a mutant deficient in zinc expulsion and the growth of a mutant of the major oxidative stress regulator SpxA1. Importantly, fructose metabolism lowered culture pH at a faster pace, allowed better survival under acidic and nutrient-depleted conditions, and enhanced the competitiveness of <i>S. mutans</i> against <i>Streptococcus sanguinis</i>, although a moderated level of F-1-P might further boost some of these benefits. Conversely, several commensal streptococcal species displayed a greater sensitivity to fructose that may negatively affect their persistence and competitiveness in dental biofilm. In conclusion, fructose metabolism is integrated into the stress core of <i>S. mutans</i> and regulates critical functions required for survival and its ability to induce dysbiosis in the oral cavity.IMPORTANCEFructose is a common monosaccharide in the biosphere, yet its overconsumption has been linked to various health problems in humans including insulin resistance, obesity, diabetes, non-alcoholic liver diseases, and even cancer. These effects are in large part attributable to the unique biochemical characteristics and metabolic responses associated with the degradation of fructose. Yet, an understanding of the effects of fructose on the physiology of bacteria and its implications for the human microbiome is severely lacking. Here, we performed a series of analyses on the gene regulation of a dental pathogen <i>Streptococcus mutans</i> by exposing it to fructose and other important stress agents. Further supported by growth, persistence, and competition assays, our findings revealed the ability of fructose to activate a set of stress-related functions that may prove critical to the ability of the bacterium to persist and cause diseases both within and without the oral cavity.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":"16 5","pages":"e0048525"},"PeriodicalIF":5.1,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12077213/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144024873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Diversification of DIX domain-containing proteins in the SAR supergroup.","authors":"Maria-Myrto Kostareli, Timo Westerink, Gabriel Couillaud, Maaria Peippo, Francine Govers, Dolf Weijers, Edouard Evangelisti","doi":"10.1128/mbio.03966-24","DOIUrl":"10.1128/mbio.03966-24","url":null,"abstract":"<p><p>Polarity establishment is crucial for development, cellular organization, and signaling in living organisms. In animals and plants, this process involves DIX domain-containing proteins (DDPs) that assemble into oligomers via head-to-tail DIX polymerization, facilitating localized protein aggregation. This study uncovers the unexpected diversity of DDPs within the SAR supergroup, characterizing four DDPs with novel domain combinations conserved in Stramenopiles and Alveolates. These proteins are predominantly found in micro-swimmers and species with a motile stage in their life cycle. We hypothesize that DDPs from these eukaryotic lineages may be involved in cell polarity-related processes, including those associated with motility. Our work provides insights for further investigations of DDPs in protists and will enable the development of evolution-informed control strategies against pathogens and parasites within this clade.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":"16 5","pages":"e0396624"},"PeriodicalIF":5.1,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12077222/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144031424","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Biochemical mapping reveals a conserved heme transport mechanism via CcmCD in System I bacterial cytochrome <i>c</i> biogenesis.","authors":"Alicia N Kreiman, Sarah E Garner, Susan C Carroll, Molly C Sutherland","doi":"10.1128/mbio.03515-24","DOIUrl":"10.1128/mbio.03515-24","url":null,"abstract":"<p><p>Heme is a redox-active cofactor for essential processes across all domains of life. Heme's redox capabilities are responsible for its biological significance but also make it highly cytotoxic, requiring tight intracellular regulation. Thus, the mechanisms of heme trafficking are still not well understood. To address this, the bacterial cytochrome <i>c</i> biogenesis pathways are being developed into model systems to elucidate mechanisms of heme trafficking. These pathways function to attach heme to apocytochrome <i>c</i>, which requires the transport of heme from inside to outside of the cell. Here, we focus on the System I pathway (CcmABCDEFGH) which is proposed to function in two steps: CcmABCD transports heme across the membrane and attaches it to CcmE. HoloCcmE then transports heme to the holocytochrome <i>c</i> synthase, CcmFH, for attachment to apocytochrome <i>c</i>. To interrogate heme transport across the membrane, we focus on CcmCD, which can form holoCcmE independent of CcmAB, leading to the hypothesis that CcmCD is a heme transporter. A structure-function analysis via cysteine/heme crosslinking identified a heme acceptance domain and heme transport channel in CcmCD. Bioinformatic analysis and structural predictions across prokaryotic organisms determined that the heme acceptance domains are structurally variable, potentially to interact with diverse heme delivery proteins. In contrast, the CcmC transmembrane heme channel is structurally conserved, indicating a common mechanism for transmembrane heme transport. We provide direct biochemical evidence mapping the CcmCD heme channel and providing insights into general mechanisms of heme trafficking by other putative heme transporters.</p><p><strong>Importance: </strong>Heme is a biologically important cofactor for proteins involved with essential cellular functions, such as oxygen transport and energy production. Heme can also be toxic to cells and thus requires tight regulation and specific trafficking pathways. As a result, much effort has been devoted to understanding how this important, yet cytotoxic, molecule is transported. While several heme transporters/importers/exporters have been identified, the biochemical mechanisms of transport are not well understood, representing a major knowledge gap. Here, the bacterial cytochrome <i>c</i> biogenesis pathway, System I (CcmABCDEFGH), is used to elucidate the transmembrane transport of heme via CcmCD. We utilize a cysteine/heme crosslinking approach, which can trap endogenous heme in specific domains, to biochemically map the heme transport channel in CcmCD, demonstrating that CcmCD is a heme transporter. These results suggest a model for heme trafficking by other heme transporters in both prokaryotes and eukaryotes.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0351524"},"PeriodicalIF":5.1,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12077264/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143752767","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cellular SLC35B4 promotes internalization during influenza A virus entry.","authors":"Guangwen Wang, Li Jiang, Ya Yan, Fandi Kong, Qibing Li, Jie Zhang, Shuangshuang Hou, Bo Wang, Xiurong Wang, Huihui Kong, Guohua Deng, Jianzhong Shi, Guobin Tian, Xianying Zeng, Hualan Chen, Chengjun Li","doi":"10.1128/mbio.00194-25","DOIUrl":"10.1128/mbio.00194-25","url":null,"abstract":"<p><p>SLC35B4, a nucleotide sugar transporter that mediates the transport of UDP-GlcNAc and UDP-xylose, was found to be required for the replication of influenza A virus (IAV) of the H5N1 subtype in our genome-wide siRNA library screen. We found that defective IAV replication in SLC35B4-deficient A549 cells was independent of virus strain specificity, and the virulence of IAV in Slc35b4 knockdown mice was also decreased. By examining the individual stages of the IAV replication cycle, we discovered that the amount of internalized IAV was significantly reduced in SLC35B4-knockout A549 cells. Mechanistically, SLC35B4 facilitated IAV replication by transporting UDP-xylose, which attaches to the serine residue of heparan sulfate proteoglycans (HSPGs) in the heparan sulfate (HS) biosynthesis pathway. Knockdown of associated host factors (i.e., XYLT2, B4GALT7, EXT1, and EXT2) in the HS biosynthesis pathway also impaired IAV replication. Furthermore, we revealed that AGRN, a unique HSPG family member, was important for the endocytosis of IAV in A549 cells. Moreover, we found that the homeostasis of the AGRN protein was regulated by HS modification mediated by the initial UDP-xylose transporter SLC35B4, thereby affecting the expression level of endocytic adapter AP2B1 to influence IAV internalization. Collectively, these findings establish that SLC35B4 is an important regulator of IAV replication and uncover the underlying mechanisms by which SLC35B4 employs UDP-xylose transport activity to promote IAV internalization.IMPORTANCEThe entry process of IAV represents a favorable target for drug development. In this study, we identified SLC35B4 as an important host factor for the efficient replication of different subtypes of IAV <i>in vitro</i> and for the virulence of IAV in mice. We revealed that SLC35B4 employed its UDP-xylose transport activity to promote the HS biosynthesis pathway, thereby assisting IAV internalization into target cells in the early stage of viral infection. Consistently, several downstream factors in the HS biosynthesis pathway, i.e., XYLT2, B4GALT7, EXT1, and EXT2, as well as a specific HSPG member AGRN were also important for the replication of IAV. Furthermore, the UDP-xylose-transporting activity of SLC35B4 was involved in the regulation of the homeostasis of the AGRN protein by HS modification, which influenced virus internalization by affecting the expression levels of AP2B1. Together, the identification of the SLC35B4-XYLT2-B4GALT7-EXT1-EXT2-AGRN-AP2B1 axis may shed light on the development of potential anti-IAV therapeutics.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0019425"},"PeriodicalIF":5.1,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12077083/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143700965","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Functional characterization of a novel protein-coding circular RNA, circRNA_1193, from the <i>mAAP</i> gene in silkworm and its role in antiviral defense against BmCPV.","authors":"Song Li, Zeen Shen, Hongchuan Zhao, Xialing Chen, Qunnan Qiu, Xinyu Tong, Min Zhu, Xing Zhang, Chengliang Gong, Xiaolong Hu","doi":"10.1128/mbio.00125-25","DOIUrl":"10.1128/mbio.00125-25","url":null,"abstract":"<p><p>A novel circular RNA, circRNA_1193, which originates from the <i>membrane alanyl aminopeptidase-like</i> gene in silkworms, was explored for its potential function and regulatory mechanism. We validated the presence of circRNA_1193 in <i>Bombyx mori</i> cytoplasmic polyhedrosis virus (BmCPV)-infected silkworm ovary cell line (BmN) cells through a combination of reverse transcription polymerase chain reaction, Northern blotting, and <i>in situ</i> hybridization. CircRNA_1193 exhibited tissue-specific expression, being highly enriched in the midgut and Malpighian tubules, and displayed a specific response to BmCPV infection, but not to <i>Bombyx mori</i> nucleopolyhedrovirus or lipopolysaccharide. Functional analyses revealed that the overexpression of circRNA_1193 suppressed BmCPV replication, whereas its knockdown increased viral replication. Bioinformatic analyses revealed potential internal ribosome entry sites, m6A methylation sites, and open reading frames (ORFs) within circRNA_1193, suggesting its potential coding capacity. We confirmed the translation of the ORF by constructing a DsRed reporter vector and demonstrating DsRed expression in transfected cells. Furthermore, a mutation of the start codon within circRNA_1193 abolished its antiviral activity, highlighting the crucial role of the translated protein, which is 35 kDa and is designated as VSP35. Furthermore, our data suggest that the formation of circRNA_1193 relies on reverse complementary flanking sequences. These findings unveil a novel protein-coding circular RNA in silkworms that plays a critical role in antiviral defense.</p><p><strong>Importance: </strong>This study identified a novel circular RNA, circRNA_1193, in the silkworm <i>Bombyx mori</i>, and revealed its critical role in antiviral defense against <i>Bombyx mori</i> cytoplasmic polyhedrosis virus (BmCPV). We demonstrated that circRNA_1193 exhibits tissue-specific expression, is upregulated in response to BmCPV infection, and possesses antiviral activity. Importantly, we show that circRNA_1193 encodes the viral protein VSP35, which is essential for its antiviral function. These findings provide new insights into the complex regulatory mechanisms of circular RNAs in antiviral immunity and underscore the potential of circular RNAs as therapeutic targets in viral diseases. The identification of a protein-coding circular RNA with antiviral activity in <i>B. mori</i> has broader implications for understanding the evolution and diversity of host defense mechanisms against viruses.</p>","PeriodicalId":18315,"journal":{"name":"mBio","volume":" ","pages":"e0012525"},"PeriodicalIF":5.1,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12077084/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143730733","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}