A Model for Allosteric Communication in Drug Transport by the AcrAB-TolC Tripartite Efflux Pump

RND family efflux pumps are complex macromolecular machines involved in multidrug resistance by extruding antibiotics from the cell. While structural studies and molecular dynamics simulations have provided insights into the architecture and conformational states of the pumps, the path followed by conformational changes from the inner membrane protein (IMP) to the periplasmic membrane fusion protein (MFP) and to the outer membrane protein (OMP) in tripartite efflux assemblies is not fully understood. Here, we investigated AcrAB-TolC efflux pump’s allostery by comparing resting and transport states using difference distance matrices supplemented with evolutionary couplings data and buried surface area measurements. Our analysis indicated that substrate binding by the IMP triggers quaternary level conformational changes in the MFP, which induce OMP to switch from the closed state to the open state, accompanied by a considerable increase in the interface area between the MFP subunits and between the OMPs and MFPs. This suggests that the pump’s transport-ready state is at a more favourable energy level than the resting state, but raises the puzzle of how the pump does not become stably trapped in a transport-intermediate state. We propose a model for pump allostery that includes a downhill energetic transition process from a proposed ‘activated’ transport state back to the resting pump.

Two Cholesterol Recognition Amino Acid Consensus Motifs of GP64 with Uncleaved Signal Peptide Are Required for Bombyx mori Nucleopolyhedrovirus Infection

BmNPV is a severe pathogen that mainly infects silkworms. GP64 is the key membrane fusion protein that mediates BmNPV infection, and some studies have indicated that cholesterol and lipids are involved in BmNPV infection.

The Viral Class II Membrane Fusion Machinery: Divergent Evolution from an Ancestral Heterodimer

A key step during the entry of enveloped viruses into cells is the merger of viral and cell lipid bilayers. This process is driven by a dedicated membrane fusion protein (MFP) present at the virion surface, which undergoes a membrane–fusogenic conformational change triggered by interactions with the target cell. Viral MFPs have been extensively studied structurally, and are divided into three classes depending on their three-dimensional fold. Because MFPs of the same class are found in otherwise unrelated viruses, their intra-class structural homology indicates horizontal gene exchange. We focus this review on the class II fusion machinery, which is composed of two glycoproteins that associate as heterodimers. They fold together in the ER of infected cells such that the MFP adopts a conformation primed to react to specific clues only upon contact with a target cell, avoiding premature fusion in the producer cell. We show that, despite having diverged in their 3D fold during evolution much more than the actual MFP, the class II accompanying proteins (AP) also derive from a distant common ancestor, displaying an invariant core formed by a β-ribbon and a C-terminal immunoglobulin-like domain playing different functional roles—heterotypic interactions with the MFP, and homotypic AP/AP contacts to form spikes, respectively. Our analysis shows that class II APs are easily identifiable with modern structural prediction algorithms, providing useful information in devising immunogens for vaccine design.

A bioactive phlebovirus-like envelope protein in a hookworm endogenous virus

Endogenous viral elements (EVEs), accounting for 15% of our genome, serve as a genetic reservoir from which new genes can emerge. Nematode EVEs are particularly diverse and informative of virus evolution. We identify Atlas virus - an intact retrovirus-like EVE in the human hookworm Ancylostoma ceylanicum, with an envelope protein genetically related to GN-GC glycoproteins from phleboviruses. A cryo-EM structure of Atlas GC reveals a class II viral membrane fusion protein fold not previously seen in retroviruses. Atlas GC has the structural hallmarks of an active fusogen. Atlas GC trimers insert into membranes with endosomal lipid compositions and low pH. When expressed on the plasma membrane, Atlas GC has cell-cell fusion activity. RNA-Seq data analysis detected transcripts mapping to Atlas virus at different stages of hookworm development. With its preserved biological activities, Atlas GC has the potential to acquire a cellular function. Our work reveals structural plasticity in reverse-transcribing RNA viruses.

Engineering of extracellular vesicles for small molecule-regulated cargo loading and cytoplasmic delivery of bioactive proteins

Cytoplasmic delivery of functional proteins into target cells remains challenging for many biological agents to exert their therapeutic effects. Extracellular vesicles (EVs) are expected to be a promising platform for protein delivery; however, efficient loading of proteins of interest (POIs) into EVs remains elusive. In this study, we utilized small compound-induced heterodimerization between FK506 binding protein (FKBP) and FKBP12-rapamycin-binding (FRB) domain, to sort bioactive proteins into EVs using the FRB-FKBP system. When CD81, a typical EV marker protein, and POI were fused with FKBP and FRB, respectively, rapamycin induced the binding of these proteins through FKBP-FRB interaction and recruited the POIs into EVs. The released EVs, displaying virus-derived membrane fusion protein, delivered the POI cargo into recipient cells and their functionality in the recipient cells was confirmed. Furthermore, we demonstrated that CD81 could be replaced with other EV-enriched proteins, such as CD63 or HIV Gag. Thus, the FRB-FKBP system enables the delivery of functional proteins and paves the way for EV-based protein delivery platforms.

SNAP47 Interacts with ATG14 to Promote VP1 Conjugation and CVB3 Propagation

Coxsackievirus B3 (CVB3), an enterovirus (EV) in the family of Picornaviridae, is a global human pathogen for which effective antiviral treatments and vaccines are lacking. Previous research demonstrated that EV-D68 downregulated the membrane fusion protein SNAP47 (synaptosome associated protein 47) and SNAP47 promoted EV-D68 replication via regulating autophagy. In the current study, we investigated the interplay between CVB3 and cellular SNAP47 using HEK293T/HeLa cell models. We showed that, upon CVB3 infection, protein levels of SNAP47 decreased independent of the activity of virus-encoded proteinase 3C. We further demonstrated that the depletion of SNAP47 inhibited CVB3 infection, indicating a pro-viral function of SNAP47. Moreover, we found that SNAP47 co-localizes with the autophagy-related protein ATG14 on the cellular membrane fractions together with viral capsid protein VP1, and expression of SNAP47 or ATG14 enhanced VP1 conjugation. Finally, we revealed that disulfide interactions had an important role in strengthening VP1 conjugation. Collectively, our study elucidated a mechanism by which SNAP47 and ATG14 promoted CVB3 propagation through facilitating viral capsid assembly.

The SARS-CoV-2 host cell membrane fusion protein TMPRSS2 is a tumor suppressor and its downregulation promotes antitumor immunity and immunotherapy response in lung adenocarcinoma

Background Cancer patients are susceptible to SARS-CoV-2 infection. An investigation into the association between the SARS-CoV-2 host cell membrane fusion protein TMPRSS2 and lung cancer is significant, considering that lung cancer is the leading cause of cancer death and that the lungs are the primary organ SARS-CoV-2 attacks. Methods Using five lung adenocarcinoma (LUAD) genomics datasets, we explored associations between TMPRSS2 expression and immune signatures, cancer-associated pathways, tumor progression phenotypes, and clinical prognosis in LUAD by the bioinformatics approach. We validated the findings from the bioinformatics analysis through in vitro and in vivo experiments and clinical samples we collected. Results TMPRSS2 expression levels were negatively correlated with the enrichment levels of both antitumor immune signatures and immunosuppressive signatures in LUAD. However, TMPRSS2 expression levels showed a significant positive correlation with the ratios of immune-stimulatory/immune-inhibitory signatures (CD8 + T cells/PD-L1) in LUAD. TMPRSS2 downregulation correlated with elevated activities of many oncogenic pathways in LUAD, including cell cycle, mismatch repair, p53, and extracellular matrix signaling. TMPRSS2 downregulation correlated with increased proliferation, stemness, genomic instability, tumor advancement, and worse survival in LUAD. In vitro and in vivo experiments validated the association of TMPRSS2 deficiency with increased tumor cell proliferation and invasion and antitumor immunity in LUAD. Moreover, in vivo experiments demonstrated that TMPRSS2-knockdown tumors were more sensitive to BMS-1, an inhibitor of PD-1/PD-L1. Conclusion TMPRSS2 is a tumor suppressor, while its downregulation is a positive biomarker of immunotherapy in LUAD. Our data provide a connection between lung cancer and pneumonia caused by SARS-CoV-2 infection.

The SARS-CoV-2 host cell membrane fusion protein TMPRSS2 is a tumor suppressor and its downregulation correlates with increased antitumor immunity and immunotherapy response in lung adenocarcinoma

Background TMPRSS2 is a host cell membrane fusion protein for SARS-CoV-2 invading human host cells. It also has an association with cancer, particularly prostate cancer. However, its association with lung cancer remains insufficiently explored. Thus, an in-depth investigation into the association between TMPRSS2 and lung cancer is significant, considering that lung cancer is the leading cause of cancer death and that the lungs are the primary organ SARS-CoV-2 attacks. Methods Using five lung adenocarcinoma (LUAD) genomics datasets, we explored associations between TMPRSS2 expression and immune signatures, cancer-associated pathways, tumor progression phenotypes, and clinical prognosis in LUAD by the bioinformatics approach. Furthermore, we validated the findings from the bioinformatics analysis by performing in vitro experiments with the human LUAD cell line A549 and in vivo experiments with mouse tumor models. We also validated our findings in LUAD patients from Jiangsu Cancer Hospital, China. Results TMPRSS2 expression levels were negatively correlated with the enrichment levels of CD8+ T and NK cells and immune cytolytic activity in LUAD, which represent antitumor immune signatures. Meanwhile, TMPRSS2 expression levels were negatively correlated with the enrichment levels of CD4+ regulatory T cells and myeloid-derived suppressor cells and PD-L1 expression levels in LUAD, which represent antitumor immunosuppressive signatures. However, TMPRSS2 expression levels showed a significant positive correlation with the ratios of immune-stimulatory/immune-inhibitory signatures (CD8+ T cells/PD-L1) in LUAD. It indicated that TMPRSS2 levels had a stronger negative correlation with immune-inhibitory signatures than with immune-stimulatory signatures. TMPRSS2 downregulation correlated with elevated activities of many oncogenic pathways in LUAD, including cell cycle, mismatch repair, p53, and extracellular matrix (ECM) signaling. TMPRSS2 downregulation correlated with increased proliferation, stemness, genomic instability, tumor advancement, and worse survival in LUAD. In vitro and in vivo experiments validated the association of TMPRSS2 deficiency with increased tumor cell proliferation and invasion and antitumor immunity in LUAD. Moreover, in vivo experiments demonstrated that TMPRSS2-knockdown tumors were more sensitive to BMS-1, an inhibitor of PD-1/PD-L1. Conclusions TMPRSS2 is a tumor suppressor, while its downregulation is a positive biomarker of immunotherapy in LUAD. Our data provide a connection between lung cancer and pneumonia caused by SARS-CoV-2 infection.

Transcriptional regulation of the virulence genes and the biofilm formation associated operons in Vibrio parahaemolyticus

Background The membrane fusion protein (mfp) gene locus of Vibrio parahaemolyticus consists of two operons, cpsQ-mfpABC and mfpABC, which are both required for biofilm formation. ToxR and CalR are required for the full virulence of V. parahaemolyticus, and their mutual regulation has been demonstrated. Moreover, cell density-dependent expression of toxR was previously observed in V. parahaemolyticus, but details about the related mechanisms remained unclear. QsvR can work with the master quorum sensing (QS) regulators AphA and OpaR to regulate virulence expression and biofilm formation. Results In the present work, we showed that QsvR bound to the promoter-proximal DNA regions of toxR and calR to repress their transcription as well as occupying the regulatory regions of cpsQ-mfpABC and mfpABC to activate their transcription. Thus, we reconstructed the QsvR-dependent promoter organization of toxR, calR, cpsQ-mfpABC, and mfpABC. Conclusion QsvR directly repressed toxR and calR transcription as well as directly activated cpsQ-mfpABC and mfpABC transcription. The data presented here promotes us to gain deeper knowledge of the regulatory network of the mfp locus in V. parahaemolyticus.

Reporter gene assay for membrane fusion of extracellular vesicles

Extracellular vesicles (EVs) secreted by living cells are expected to deliver biological cargo molecules, including RNA and proteins, to the cytoplasm of recipient cells. There is an increasing need to understand the mechanism of intercellular cargo delivery by EVs. However, the lack of a feasible bioassay has hampered our understanding of the biological processes of EV uptake, membrane fusion, and cargo delivery to recipient cells. Here, we describe a reporter gene assay that can measure the membrane fusion efficiency of EVs during cargo delivery to recipient cells. When EVs containing tetracycline transactivator (tTA)-fused tetraspanins are internalized by recipient cells and fuse with cell membranes, the tTA domain is exposed to the cytoplasm and cleaved by protease to induce tetracycline responsive element (TRE)-mediated reporter gene expression in recipient cells. This assay (designated as EV-mediated tetraspanin-tTA delivery assay, ETTD assay), enabled us to assess the cytoplasmic cargo delivery efficiency of EVs in recipient cells. With the help of a vesicular stomatitis virus-derived membrane fusion protein, the ETTD assay could detect significant enhancement of cargo delivery efficiency of EVs. Furthermore, the ETTD assay could evaluate the effect of potential cargo delivery enhancers/inhibitors. Thus, the ETTD assay may contribute to a better understanding of the underlying mechanism of the cytoplasmic cargo delivery by EVs.