Endogenous retroviruses (ERVs) are remnants of ancestral viruses in the host genome. One feline ERV group V (EnvV) member, EnvV-Fca, was detected as a placenta-specific protein secreted from cells. EnvVs are classified into two groups, and genetic analyses show that EnvV2 genes are widespread in vertebrates, with birds, bats, and rodents potentially acting in virus transmission. These findings present a model of retroviral transmission and may elucidate ERV evolution.

Endogenous retroviruses (ERVs) are remnants of ancestral viruses in the host genome. The present study identified the expression of a defective retroviral env gene belonging to the ERV group V member Env (EnvV) in Felis catus (EnvV-Fca). EnV-Fca was specifically detected in the placental trophoblast syncytiotrophobic layer and expressed as a secreted protein in cultured cells. Genetic analyses indicated that EnvV2 genes are widely present in vertebrates and are under purifying selection among carnivores, suggesting a potential benefit for the host. This study suggests that birds, bats, and rodents carrying EnvV2 may play significant roles as intermediate vectors in spreading or cross-transmitting viruses among species. Our findings provide valuable insights into the evolution of ERV in vertebrate hosts.

The deubiquitinating enzyme OTUD6A deubiquitinates the TEAD4 transcription factor, enhancing its interaction with co-activator YAP over co-repressor VGLL4. This modulation promotes TEAD4 transcriptional activity, facilitating the expression of multiple target genes controlled by the YAP-TEAD complex.

TEAD transcription factors play a central role in the Hippo signaling pathway. In this study, we focused on transcriptional enhancer factor TEF-3 (TEAD4), exploring its regulation by the deubiquitinase OTU domain-containing protein 6A (OTUD6A). We identified OTUD6A as a TEAD4-interacting deubiquitinase, positively influencing TEAD-driven transcription without altering TEAD4 stability. Structural analyses revealed specific interaction domains: the N-terminal domain of OTUD6A and the YAP-binding domain of TEAD4. Functional assays demonstrated the positive impact of OTUD6A on the transcription of YAP–TEAD target genes. Despite no impact on TEAD4 nuclear localization, OTUD6A selectively modulated nuclear interactions, enhancing YAP–TEAD4 complex formation while suppressing VGLL4 (transcription cofactor vestigial-like protein 4)–TEAD4 interaction. Critically, OTUD6A facilitated YAP–TEAD4 complex binding to target gene promoters. Our study unveils the regulatory landscape of OTUD6A on TEAD4, providing insights into diseases regulated by YAP–TEAD complexes.

A8iJp, a type-IV J domain protein of Plasmodium falciparum, gets truncated and trafficked into the host erythrocyte. The exported A8iJp gets localized to the lumen of the J-dots and can influence the chaperone activity of the human HSP70 chaperone HsHSPA8. Also, a subset of HsHSPA8 co-localizes with A8iJp within infected human erythrocytes. We suggest that A8iJp influences the functioning of HsHSPA8 during host erythrocyte remodeling.

Plasmodium falciparum renovates the host erythrocyte to survive during intraerythrocytic development. This renovation requires many parasite proteins to unfold and move outside the parasitophorous vacuolar membrane, and chaperone-regulated protein folding becomes essential for the exported proteins to function. We report on a type-IV J domain protein (JDP), PF3D7_1401100, which we found to be processed before export and trafficked inside the lumen of parasite-derived structures known as J-dots. We found this protein to have holdase activity, as well as stimulate the ATPase and aggregation suppression activity of the human HSP70 chaperone HsHSPA8; thus, we named it “HSPA8-interacting J protein” (A8iJp). Moreover, we found a subset of HsHSPA8 to co-localize with A8iJp inside the infected human erythrocyte. Our results suggest that A8iJp modulates HsHSPA8 chaperone activity and may play an important role in host erythrocyte renovation.

MPER-targeting antibodies display nearly pan-neutralizing activity against HIV. Elucidating the mechanisms of epitope recognition by these antibodies is paramount for developing preventive vaccines and antibody-based treatments. Here, we report that binding of 10E8 to the MPER helix epitope presented in the membrane microenvironment occurs in two steps: (i) engagement with the solvent-exposed MPER portion; and (ii) accommodation of the membrane surface.

HIV-1 antibodies targeting the carboxy-terminal area of the membrane-proximal external region (ctMPER) are close to exerting viral pan-neutralization. Here, we reconstituted the ctMPER epitope as the N-terminal extremity of the Env glycoprotein transmembrane domain helix and immobilized it onto biosensor-supported lipid bilayers. We assessed the binding mechanism of anti-MPER antibody 10E8 through Surface Plasmon Resonance, and found, through equilibrium and kinetic binding analyses as a function of bilayer thickness, peptide length, and paratope mutations, that 10E8 engages first with the epitope peptide (encounter), limited by ctMPER helix accessibility at the membrane surface, and then inserts into the lipid bilayer assisted by favorable Fab-membrane interactions (docking). This mechanistic information may help in devising new strategies to develop more efficient MPER-targeting vaccines.

In this study, we report a systematic assessment of AlphaFold performance to predict 9 different human MED25 ACID domain–transactivation domain (TAD) interfaces and evaluate the accuracy of the models through comparison with published and new experimental data. We also reveal a new interaction surface unique to plants by predicting 3 different Arabidopsis thaliana MED25 complexes.

The human Mediator complex subunit MED25 binds transactivation domains (TADs) present in various cellular and viral proteins using two binding interfaces, named H1 and H2, which are found on opposite sides of its ACID domain. Here, we use and compare deep learning methods to characterize human MED25–TAD interfaces and assess the predicted models to published experimental data. For the H1 interface, AlphaFold produces predictions with high-reliability scores that agree well with experimental data, while the H2 interface predictions appear inconsistent, preventing reliable binding modes. Despite these limitations, we experimentally assess the validity of MED25 interface predictions with the viral transcriptional activators Lana-1 and IE62. AlphaFold predictions also suggest the existence of a unique hydrophobic pocket for the Arabidopsis MED25 ACID domain.

Here, we report the first crystal structure of PaIch at 1.98 Å resolution. A unique N-terminal hotdog fold containing a short helical segment α3-, named an “eaten sausage”, slipped away from the conserved β-sheet scaffold, whereas central helices of other N- as well as C-terminal hotdog fold containing hydratases are properly wrapped up by their respective β-sheet scaffold.

Itaconyl-CoA hydratase in Pseudomonas aeruginosa (PaIch) converts itaconyl-CoA to (S)-citramalyl-CoA upon addition of a water molecule, a part of an itaconate catabolic pathway in virulent organisms required for their survival in humans host cells. Crystal structure analysis of PaIch showed that a unique N-terminal hotdog fold containing a 4-residue short helical segment α3-, named as an “eaten sausage”, followed by a flexible loop region slipped away from the conserved β-sheet scaffold, whereas the C-terminal hotdog fold is similar to all MaoC. A conserved hydratase motif with catalytic residues provides mechanistic insights into catalysis, and existence of a longer substrate binding tunnel may suggest the binding of longer CoA derivatives.

The Skraban-Deardorff intellectual disability syndrome (SKDEAS) is associated with diverse mutations in WDR26, encoding a subunit required to assemble a giant oval-shaped supramolecular CTLH E3 ubiquitin ligase complex and substrate recruitment. Structural modeling of SKDEAS-associated mutations combined with functional assays revealed impaired CTLH E3 complex assembly and interactions, thus providing first mechanistic insights into SKDEAS pathology.

Patients with Skraban-Deardorff syndrome (SKDEAS), a neurodevelopmental syndrome associated with a spectrum of developmental and intellectual delays and disabilities, harbor diverse mutations in WDR26, encoding a subunit of the multiprotein CTLH E3 ubiquitin ligase complex. Structural studies revealed that homodimers of WDR26 bridge two core-CTLH E3 complexes to generate giant, hollow oval-shaped supramolecular CTLH E3 assemblies. Additionally, WDR26 mediates CTLH E3 complex binding to subunit YPEL5 and functions as substrate receptor for the transcriptional repressor HBP1. Here, we mapped SKDEAS-associated mutations on a WDR26 structural model and tested their functionality in complementation studies using genetically engineered human cells lacking CTLH E3 supramolecular assemblies. Despite the diversity of mutations, 15 of 16 tested mutants impaired at least one CTLH E3 complex function contributing to complex assembly and interactions, thus providing first mechanistic insights into SKDEAS pathology.