Dimer Interface Research Articles

Structural basis for inositol pyrophosphate gating of the phosphate channel XPR1.

Precise regulation of intracellular phosphate (Pi) is critical for cellular function, with xenotropic and polytropic retrovirus receptor 1 (XPR1) serving as the sole Pi exporter in humans. The mechanism of Pi efflux, activated by inositol pyrophosphates (PP-IPs), has remained unclear. This study presents cryo-electron microscopy structures of XPR1 in multiple conformations, revealing a transmembrane pathway for Pi export and a dual-binding activation pattern for PP-IPs. A canonical binding site is located at the dimeric interface of Syg1/Pho81/XPR1 (SPX) domains, and a second site, biased toward PP-IPs, is found between the transmembrane and SPX domains. By integrating structural studies with electrophysiological analyses, we characterized XPR1 as an inositol phosphates (IPs)/PP-IPs-activated phosphate channel. The interplay among its transmembrane domains, SPX domains, and IPs/PP-IPs orchestrates the conformational transition between its closed and open states.

Design and Evaluation of Peptide Inhibitors Targeting the Dimerization of SARS-CoV-2 Main Protease.

The severe acute respiratory syndrome virus 2 (SARS-CoV-2) seriously impacted public health. The evolutionarily conserved viral chymotrypsin-like main protease (Mpro) is an important target for anti-SARS-CoV-2 drug development. Previous studies have shown that the eight N-terminal amino acids (N8) of SARS-CoV Mpro are essential for its dimerization, and are used to design inhibitors against SARS-CoV Mpro dimerization. Here, we established a simple readout assay using SDS-PAGE and Coomassie blue staining to measure inhibitory activity of N8 peptide derived from SARS-CoV-2 Mpro. To optimize its inhibitory effect, we then modified the side-chain length, charge, and hydrophilicity of the N8 peptide, and introduced a mutated Mpro recognition sequence. As a result, we obtained a series of potent peptide inhibitors against SARS-CoV-2 Mpro, with N8-A24 being the most efficient with an IC50 value of 1.44 mM. We observed that N8-A24 reduced Mpro dimerization with an IC50 value of 0.86 mM. Molecular docking revealed that N8-A24 formed hydrogen bond interactions with critical dimeric interface residues, thus inhibiting its dimerization and activity. In conclusion, our study not only discovers a series of peptide inhibitors targeting the SARS-CoV-2 Mpro dimerization, but also provides a promising strategy for the rational design of new inhibitors against COVID-19.

IMMU-26. TARGETING CHK2-YBX1/3 INTERACTION TO OVERCOME IMMUNOSUPPRESSION IN GLIOMAS

Abstract Whereas the contribution of tumor microenvironment to the profound immune suppression of glioblastoma (GBM) is clear, tumor-cell intrinsic mechanisms that regulate resistance to CD8 T cells are less studied. We performed an in vivo CRISPR screen to identify glioma intrinsic kinases that contribute to evasion of tumor cells from CD8 T cells. The screen revealed a DNA damage response gene-checkpoint kinase 2 (Chek2) to be the most important kinase contributing to escape from CD8 T-cell recognition. Genetic depletion or pharmacological inhibition of Chek2 with blood-brain-barrier permeable drugs that are in the clinical trials, in combination with PD-1/PD-L1 blockade, led to survival benefit in preclinical glioma models. Analysis of human GBMs demonstrated that Chek2 expression is inversely associated with antigen presentation and T-cell activation. However, the mechanism underlying the immunosuppressive function of Chek2 in gliomas is unknown. Here, we identified that glioma tumor cell intrinsic Chek2 interacts with Y-Box Binding Protein 1 and 3 (Ybx1&3) in ex vivo gliomas using immunoprecipitation followed by mass spectrometry. Independently, YBX3 was also identified as one of the most significantly phosphorylated protein upon Chek2 knockout using phosphoproteomics analysis. The YBX1&3 are DNA/RNA binding proteins implicated in transcriptional regulation of immune-modulatory genes. In silico docking using Alphafold and PIPER tool in Schrodinger revealed that the YBX1 cold-shock domain interacted near the ATP/ADP binding site in CHK2. This interface was also part of the CHK2-CHK2 dimer interface. Consistent with our model, disruption of CHK2 dimerization using prexasertib led to increased colocalization of CHK2-YBX1 in human GBM patient derived xenograft cells. Further, targeting of CHK2-YBX1 interaction with YBX1 inhibitor SU056 reversed the repression of IFNγ response genes in glioma cells. Together this study unveils a kinase independent (non-catalytic) function of CHK2, providing insight into the non-canonical immunosuppressive role of CHK2 in gliomas.

A Novel Regulatory Motif at the Hinge Dimer Interface of the MksB Mediates Dimerization and DNA Binding Activity.

The Structural Maintenance of Chromosome (SMC) protein is essential for various cellular processes, including chromosome organization, DNA repair, and genome stability. MksB, an alternative SMC protein present in prokaryotes, comprises a hinge dimerization domain and an ABC ATPase head domain linked by a coiled-coil arm. While hinge dimerization in bacterial and eukaryotic SMCs is attributed to conserved glycines, our study unveils the critical role of a novel KDDR motif located at a loop near the hinge dimer interface in Mycobacterium smegmatis MksB (MsMksB). We demonstrate the regulatory role of this motif in MsMksB dimerization and DNA binding activity. The K600D mutation in the KDDR motif induces MsMksB dimer-to-monomer conversion, highlighting the significance of this motif in MsMksB dimerization. Mass spectrometry-based mapping of the DNA binding site revealed the lysine's involvement in protein-DNA interaction. Monomers of the hinge domain lose DNA binding activity, and MsMksB single-arm mutants exhibit reduced DNA binding and ATPase activity, underscoring the importance of hinge-mediated dimerization in MsMksB function. Notably, the R603D mutant retains dimerization but shows compromised ATPase and DNA binding activities. Mutants with defective ATPase activity exhibit impaired DNA condensation in vivo. These findings provide novel regulatory insight into the mechanism of MksB dimerization and DNA binding, uncovering the fundamental processes of chromosome condensation and segregation.

Influence of Cataract Causing Mutations on αA-Crystallin: A Computational Approach.

The αA-crystallin protein plays a vital role in maintaining the refractive index and transparency of the eye lens. Significant clinical studies have emerged as the αA-crystallin is prone to aggregation, resulting in the formation of cataracts with varied etiologies due to mutations. This work aims to comprehend the structural and functional role of cataract-causing mutations in αA-crystallin, particularly at N-Terminal and α-Crystallin Domains, using in-silico approaches including molecular dynamics simulation. About 19 mutants of αA-crystallin along with native structure were simulated for 100 ns and the post-simulations analyses reveal pronounced dynamics of αA-crystallin due to the enhanced structure flexibility as its native compactness was lost and is witnessed mainly by the mutants R12L, R21L, R21Q, R54L, R65Q, R116C and R116H. It is observed that αA-crystallin discloses the NTD motions as the dominant one and the same was endorsed by the linear variation between Rg and the center-of-mass of αA-crystallin. Interestingly, such enhanced dynamics of αA-crystallin mutants associated with the structure flexibility is internally modulated by the dynamic exchange of secondary structure elements β-sheets and coils (R2 = 0.619) during simulation. Besides, the observed pronounced dynamics of dimer interface region (β3-L6-β4 segment) of ACD along with CTD dynamics also gains importance. Particularly, the highly dynamic mutants are also characterized by enhanced non-covalent and hydrophobic interactions which renders detrimental effects towards its stability, and favours possible protein unfolding mechanisms. Overall, this study highlights the mutation-mediated structural distortions in αA-crystallin and demands the need for further potential development of inhibitors against cataract formation.

Structural Insights into the Iodothyronine Deiodinase 2 Catalytic Core and Deiodinase Catalysis and Dimerization

Iodothyronine deiodinases (Dio) are selenocysteine-containing membrane enzymes that activate and inactivate the thyroid hormones (TH) through reductive iodide eliminations. The three deiodinase isoforms are homodimers sharing highly conserved amino acid sequences, but they differ in their regioselectivities for the deiodination reaction and regulatory features. We have now solved a crystal structure of the mouse deiodinase 2 (Dio2) catalytic domain. It reveals a high overall similarity to the deiodinase 3 structure, supporting the proposed common mechanism, but also Dio2-specific features, likely mediating its unique properties. Activity studies with an artificially enforced Dio dimer further confirm that dimerization is required for activity and requires both the catalytic core and the enzyme’s N-terminus. Cross-linking studies reveal the catalytic core’s dimerization interface, providing insights into the architecture of the complete, active Dio homodimer.

Structural basis for regulation of a CBASS-CRISPR-Cas defense island by a transmembrane anti-σ factor and its ECF σ partner.

How CRISPR-Cas and cyclic oligonucleotide-based antiphage signaling systems (CBASS) are coordinately deployed against invaders remains unclear. We show that a locus containing two CBASS and one type III-B CRISPR-Cas system, regulated by the transmembrane anti-σ DdvA and its cognate extracytoplasmic function (ECF) σ DdvS, can defend Myxococcus xanthus against a phage. Cryo-electron microscopy reveals DdvA-DdvS pairs assemble as arrow-shaped transmembrane dimers. Each DdvA periplasmic domain adopts a separase/craspase-type tetratricopeptide repeat (TPR)-caspase HetF-associated with TPR (TPR-CHAT) architecture with an incomplete His-Cys active site, lacking three α-helices conserved among CHAT domains. Each active site faces the dimer interface, raising the possibility that signal-induced caspase-like DdvA autoproteolysis in trans precedes RseP-mediated intramembrane proteolysis and DdvS release. Nuclear magnetic resonance reveals a DdvA cytoplasmic CHCC-type zinc-bound three-helix bundle that binds to DdvS σ2 and σ4 domains, undergoing σ4-induced helix extension to trap DdvS. Altogether, we provide structural-mechanistic insights into membrane anti-σ-ECF σ regulation of an antiviral CBASS-CRISPR-Cas defense island.

Molecular mechanism of IgE-mediated FcεRI activation.

Allergic diseases, affecting over a quarter of individuals in industrialized countries, have become significant public health concerns1,2. The high-affinity Fc receptor for IgE (FcεRI), mainly present on mast cells and basophils, plays a crucial role in allergic diseases3-5. Monomeric IgE binding to FcεRI regulates mast cell survival, differentiation, and maturation6-8. However, the underlying molecular mechanism remains unclear. Here we demonstrate that, prior to IgE binding, FcεRI mostly exists as a homo-dimer on human mast cell membrane. The structure of human FcεRI confirms the dimeric organization, with each promoter comprising one α subunit, one β subunit, and two γ subunits. The transmembrane helices of the α subunits form a layered arrangement with those of the γ and β subunits. The dimeric interface is mediated by a four-helix bundle of the α and γ subunits at the intracellular juxtamembrane region. Cholesterol-like molecules embedded within the transmembrane domain may stabilize the dimeric assembly. Upon IgE binding, the dimeric FcεRI dissociates into two protomers, each binding to an IgE molecule. Importantly, this process elicits transcriptional activation of Egr1/3 and Ccl2 in rat basophils, which can be attenuated by inhibiting the FcεRI dimer-to-monomer transition. Collectively, our study unveils the mechanism of antigen-independent, IgE-mediated FcεRI activation.

The structural and mechanistic bases for the viral resistance to allosteric HIV-1 integrase inhibitor pirmitegravir.

Allosteric HIV-1 integrase (IN) inhibitors (ALLINIs) are investigational antiretroviral agents that potently impair virion maturation by inducing hyper-multimerization of IN and inhibiting its interaction with viral genomic RNA. The pyrrolopyridine-based ALLINI pirmitegravir (PIR) has recently advanced into phase 2a clinical trials. Previous cell culture-based viral breakthrough assays identified the HIV-1(Y99H/A128T IN) variant that confers substantial resistance to this inhibitor. Here, we have elucidated the unexpected mechanism of viral resistance to PIR. Although both Tyr99 and Ala128 are positioned within the inhibitor binding V-shaped cavity at the IN catalytic core domain (CCD) dimer interface, the Y99H/A128T IN mutations did not substantially affect the direct binding of PIR to the CCD dimer or functional oligomerization of full-length IN. Instead, the drug-resistant mutations introduced a steric hindrance at the inhibitor-mediated interface between CCD and C-terminal domain (CTD) and compromised CTD binding to the CCDY99H/A128T + PIR complex. Consequently, full-length INY99H/A128T was substantially less susceptible to the PIR-induced hyper-multimerization than the WT protein, and HIV-1(Y99H/A128T IN) conferred >150-fold resistance to the inhibitor compared with the WT virus. By rationally modifying PIR, we have developed its analog EKC110, which readily induced hyper-multimerization of INY99H/A128T in vitro and was ~14-fold more potent against HIV-1(Y99H/A128T IN) than the parent inhibitor. These findings suggest a path for developing improved PIR chemotypes with a higher barrier to resistance for their potential clinical use.IMPORTANCEAntiretroviral therapies save the lives of millions of people living with HIV (PLWH). However, the evolution of multi-drug-resistant viral phenotypes is a major clinical problem, and there are limited or no treatment options for heavily treatment-experienced PLWH. Allosteric HIV-1 integrase inhibitors (ALLINIs) are a novel class of antiretroviral compounds that work by a unique mechanism of binding to the non-catalytic site on the viral protein and inducing aberrant integrase multimerization. Accordingly, ALLINIs potently inhibit both wild-type HIV-1 and all drug-resistant viral phenotypes that have so far emerged against currently used therapies. Pirmitegravir, a highly potent and safe investigational ALLINI, is currently advancing through clinical trials. Here, we have elucidated the structural and mechanistic bases behind the emergence of HIV-1 integrase mutations in infected cells that confer resistance to pirmitegravir. In turn, our findings allowed us to rationally develop an improved ALLINI with substantially enhanced potency against the pirmitegravir-resistant virus.

Peptide Activator Stabilizes DJ-1 Structure and Enhances Its Activity

DJ-1 is a vital enzyme involved in the maintenance of mitochondrial health, and its mutation has been associated with an increased risk of Parkinson’s disease (PD). Effective regulation of DJ-1 activity is essential for the well-being of mitochondria, and DJ-1 is thus a potential target for PD drug development. In this study, two peptides (15EEMETIIPVDVMRRA29 and 47SRDVVICPDA56) were utilized with the aim of enhancing the activity of DJ-1. The mechanisms underlying the activity enhancement by these two peptides were investigated using hydrogen/deuterium exchange mass spectrometry (HDXMS). The HDXMS results revealed distinct mechanisms. Peptide 1 obstructs the access of solvent to the dimer interface and stabilizes the α/β hydrolase structure, facilitating substrate binding to a stabilized active site. Conversely, peptide 2 induces a destabilization of the α/β hydrolase core, enhancing substrate accessibility and subsequently increasing DJ-1 activity. The binding of these two peptides optimizes the activity site within the dimeric structure. These findings offer valuable insights into the mechanisms underlying the activity enhancement of DJ-1 by the two peptides, potentially aiding the development of new drugs that can enhance the activity of DJ-1 and, consequently, advance PD treatment.

Analysis of the dynamics of a complex, multipathway reaction: Insulin dimer dissociation.

The protein hormone insulin forms a homodimer that must dissociate to bind to its receptor. Understanding the kinetics and mechanism of dissociation is essential for rational design of therapeutic analogs. In addition to its physiological importance, this dissociation process serves as a paradigm for coupled (un)folding and (un)binding. Based on previous free energy simulations, insulin dissociation is thought to involve multiple pathways with comparable free energy barriers. Here, we analyze the mechanism of insulin dimer dissociation using a recently developed computational framework for estimating kinetic statistics from short-trajectory data. These statistics indicate that the likelihood of dissociation (the committor) closely tracks the decrease in the number of (native and nonnative) intermonomer contacts and the increase in the number of water contacts at the dimer interface; the transition state with equal likelihood of association and dissociation corresponds to an encounter complex with relatively few native contacts and many nonnative contacts. We identify four pathways out of the dimer state and quantify their contributions to the rate, as well as their exchange, by computing reactive fluxes. We show that both the pathways and their extents of exchange can be understood in terms of rotations around three axes of the dimer structure. Our results provide insights into the kinetics of insulin analogues and, more generally, how to characterize complex, multipathway processes.

Targeting Human Papillomavirus 33 E2 DNA Binding Domain With Polyphenols: Unveiling Interactions Through Biophysical and In Silico Methods.

The human papillomavirus (HPV) 33 is a high-risk strain that causes lesions with potential cancerous outcomes. Its E2 protein regulates the viral protein transcription and life cycle maintenance. The DNA binding domain (DBD) of the E2 protein plays a crucial role in the viral life cycle. The DBD region of the E2 protein is particularly interesting for targeting and finding potential inhibitors to inhibit its function or dimerization. Given the limited research on HPV 33 and its proteins, the present work delved into the interaction of two natural polyphenolic compounds, resveratrol, and baicalein, with the E2 DBD of HPV 33 using biophysical and in silico studies. Fluorescence studies of the E2 DBD-polyphenol complexes showed fluorescence quenching with a binding constant of the order of 106 M-1. Circular dichroism data reveal conformational changes upon binding with the polyphenols, possibly due to distinct binding sites of the E2 DBD. Differential scanning calorimetry exhibited higher melting temperatures for the two complexes than alone DBD, suggesting the complexes' stability. ITC experiment suggested favorable binding reactions with kd values in the micromolar range. Molecular docking and dynamic simulation studies revealed that the resveratrol binds to the helical region and baicalein near the central dimeric interface of E2 DBD with a good binding affinity, forming a stable protein-ligand complex during the run of 100 ns simulation. Therefore, the current study identifies both polyphenolic compounds as promising candidates for potential antiviral drug development.

Simulation-Guided Molecular Modeling of Nisin and Lipid II Assembly and Membrane Pore Formation.

The lantibiotic pore-forming peptide nisin is a promising candidate in the fight against multidrug-resistant bacteria due to its unique structure, which allows it to disrupt bacteria in two distinct ways─Lipid II trafficking and transmembrane pore formation. However, exactly how nisin and Lipid II assemble into oligomeric pore structures in the bacterial membrane is not known. Spontaneous peptide assembly into pores is difficult to observe in even the very long-time scale molecular dynamics (MD) simulations. In this study, we adopted an MD-guided modeling approach to investigate the nisin-nisin and nisin-Lipid II associations in the membrane environment. Through extensive microsecond-time scale all-atom MD simulations, we established that nisin monomers dimerize by forming β-sheets in a POPE:POPG lipid bilayer and oligomerize further to form stable transmembrane channels. We determined that these nisin dimers use Lipid II as a dimer interface to incur enhanced stability. Our results provide a clearer understanding of the self-assembly of nisin monomers within the membrane and insights into the role of Lipid II in the structural integrity of oligomeric structures.

Establishing the Comprehensive Structure−Activity Relationship of the Natural Antibiotic Kibdelomycin/Amycolamicin

Abstract: Kibdelomycin (KBD) and amycolamicin (AMM) are potent natural antibiotics effective against antibiotic‐resistant Gram‐positive pathogens, including vancomycin‐intermediate Staphylococcus aureus (S. aureus, VISA), methicillin‐resistant S. aureus (MRSA), and quinolone‐resistant S. aureus (QRSA). Their antibacterial activity stems from an unprecedented dual mechanism: the lower binding sites occupy the adenosine triphosphate (ATP) binding pocket of bacterial type II topoisomerases, while the upper binding sites disrupt the enzyme dimer interface. This dual action, combined with their unique chemical structures, positions KBD and AMM as promising scaffolds for developing new antibiotics. However, the structure‐activity relationship (SAR) of KBD/AMM remains underexplored due to their highly complex chemical structures. In this study, we utilized total synthesis to produce KBD/AMM analogs with various site modifications and evaluated their antimicrobial activities. Our findings establish the first comprehensive SAR for KBD/AMM, paving the way for the development of novel KBD/AMM‐based antibiotics.

Establishing the Comprehensive Structure-Activity Relationship of the Natural Antibiotic Kibdelomycin/Amycolamicin.

Kibdelomycin (KBD) and amycolamicin (AMM) are potent natural antibiotics effective against antibiotic-resistant Gram-positive pathogens, including vancomycin-intermediate Staphylococcus aureus (S. aureus, VISA), methicillin-resistant S. aureus (MRSA), and quinolone-resistant S. aureus (QRSA). Their antibacterial activity stems from an unprecedented dual mechanism: the lower binding sites occupy the adenosine triphosphate (ATP) binding pocket of bacterial type II topoisomerases, while the upper binding sites disrupt the enzyme dimer interface. This dual action, combined with their unique chemical structures, positions KBD and AMM as promising scaffolds for developing new antibiotics. However, the structure-activity relationship (SAR) of KBD/AMM remains underexplored due to their highly complex chemical structures. In this study, we utilized total synthesis to produce KBD/AMM analogs with various site modifications and evaluated their antimicrobial activities. Our findings establish the first comprehensive SAR for KBD/AMM, paving the way for the development of novel KBD/AMM-based antibiotics.

Mechanism of non-competitive inhibition of the SARS-CoV-2 3CL protease dimerization: Therapeutic and clinical promise of the lichen secondary metabolite perlatolinic acid

In response to the COVID-19 pandemic, identifying effective treatments against SARS-CoV-2 has become of utmost importance. This study elucidates the mechanism by which perlatolinic acid, a lichen-derived secondary metabolite, non-competitively inhibits the dimerization of the SARS-CoV-2 3CL protease, a pivotal enzyme in the virus lifecycle. Utilising a combination of kinetic parameter determination, inhibition assays, and molecular docking studies, we demonstrate that perlatolinic acid effectively disrupts the enzymatic function by binding at the dimer interface with a measured Ki value of 0.67 μM, thereby impeding the protease catalytic activity essential for viral replication. Molecular docking studies further corroborate the binding specificity of perlatolinic acid to the dimer interface, which is attributed to the loss of key interactions essential for dimerization, consequently impairing catalytic activity, highlighting its potential as a scaffold for developing broad-spectrum antiviral drugs.Despite a dose-dependent cytotoxicity of perlatolinic acid, its TC50 is approximately 43 times higher than the Ki value.Our findings suggest that perlatolinic acid holds significant promise as a lead compound for the development of new therapeutics against COVID-19, warranting further investigation and clinical evaluation.In conclusion, the study sheds light on the therapeutic potential of natural compounds in combating SARS-CoV-2, paving the way for the exploration of lichen secondary metabolites as a reservoir of potential antiviral agents.

Discovery of Thiadiazoleamide Derivatives as Potent, Selective, and Orally Available Antagonists Disrupting Androgen Receptor Homodimer.

Androgen receptor (AR) is an important therapeutic target for prostate cancer (PCa) treatment, but prolonged use of AR antagonists has led to variant drug-resistant mutations. Since all marketed AR antagonists target the ligand binding pocket (LBP) of AR, to mitigate cross-resistance, a new drug pocket named Dimer Interface Pocket was discovered and a novel AR antagonist M17-B15 was identified. M17-B15 showed strong in vitro efficacy against PCa but had poor pharmacokinetic properties in vivo. In this study, through rational design and structure-activity relationship exploration, a series of thiadiazoleamide derivatives represented by N29 (IC50 = 0.018 μM) were identified with dominant AR antagonistic activity and remarkable anti-PCa activity in vitro. Furthermore, N29 effectively inhibited a series of typical drug-resistant AR mutants. The improved oral bioavailability of N29 facilitated its efficacy via oral administration, significantly inhibiting LNCaP xenograft tumor in vivo, presenting a promising therapeutic application for PCa.

Novel Anti-Trop2 Nanobodies Disrupt Receptor Dimerization and Inhibit Tumor Cell Growth.

Background: Trop2 (trophoblast cell-surface antigen 2) is overexpressed in multiple malignancies and is closely associated with poor prognosis, thus positioning it as a promising target for pan-cancer therapies. Despite the approval of Trop2-targeted antibody-drug conjugates (ADCs), challenges such as side effects, drug resistance, and limited efficacy persist. Recent studies have shown that the dimeric forms of Trop2 are crucial for its oncogenic functions, and the binding epitopes of existing Trop2-targeted drugs lie distant from the dimerization interface, potentially limiting their antitumor efficacy. Method: A well-established synthetic nanobody library was screened against Trop2-ECD. The identified nanobodies were extensively characterized, including their binding specificity and affinity, as well as their bioactivities in antigen-antibody endocytosis, cell proliferation, and the inhibition of Trop2 dimer assembly. Finally, ELISA based epitope analysis and AlphaFold 3 were employed to elucidate the binding modes of the nanobodies. Results: We identified two nanobodies, N14 and N152, which demonstrated high affinity and specificity for Trop2. Cell-based assays confirmed that N14 and N152 can facilitate receptor internalization and inhibit growth in Trop2-positive tumor cells. Epitope analysis uncovered that N14 and N152 are capable of binding with all three subdomains of Trop2-ECD and effectively disrupt Trop2 dimerization. Predictive modeling suggests that N14 and N152 likely target the epitopes at the interface of Trop2 cis-dimerization. The binding modality and mechanism of action demonstrated by N14 and N152 are unique among Trop2-targeted antibodies. Conclusions: we identified two novel nanobodies, N14 and N152, that specifically bind to Trop2. Importantly, these nanobodies exhibit significant anti-tumor efficacy and distinctive binding patterns, underscoring their potential as innovative Trop2-targeted therapeutics.

MECHANISMS OF TECOVIRIMAT ANTIVIRAL ACTIVITY AND POXVIRUS RESISTANCE.

Mpox is a zoonotic disease endemic in central and west Africa. However, since 2022, human-adapted mpox virus (MPXV) strains are causing large outbreaks spreading outside these regions, leading the World Health Organization to declare public health emergency twice. Tecovirimat, the most widely used drug to treat these infections, blocks viral egress through a poorly understood mechanism. Tecovirimat-resistant strains, all with mutations in the viral phospholipase F13, pose public health concerns. Herein, we report the structure of an F13 homodimer, both alone and in complex with tecovirimat. We demonstrate that tecovirimat acts as a molecular glue, inducing the dimerization of the phospholipase. F13 escape mutations in MPXV clinical isolates are at the dimer interface and prevent drug-induced dimerization in solution and cells. These findings, which decipher tecovirimat's mode of action, will allow better monitoring of poxvirus outbreaks and pave the way for developing more potent and resilient therapeutics.

Yop1 stability and membrane curvature generation propensity are controlled by its oligomerisation interface.

The DP1 family of integral membrane proteins stabilize high membrane curvature in the endoplasmic reticulum and phagophores. Mutations in the human DP1 gene REEP1 are associated with Hereditary Spastic Paraplegia type 31 and distal hereditary motor neuropathy. Four missense mutations map to a putative dimerization interface but the impact of these mutations on DP1 structure and tubule formation are unknown. Combining biophysical measurements, functional assays, and computational modeling in the context of the model protein Yop1, we found that missense mutations have variable effects on DP1 dimer structure and in vitro tubulation activity, and provide mechanistic insights into the role of DP1 oligomerisation on membrane curvature stabilization. Whereas the mutations P71L and S75F decreased dimer homogeneity and led to polydisperse oligomerization and impaired membrane curving activity, A72E introduced new polar interactions between subunits that stabilized the Yop1 dimer and allowed robust tubule formation but prevented formation of more highly-curved lipoprotein particles (LPP). The introduction of a BRIL domain to the cytoplasmic loop of A72E rescued LPP formation, consistent with a requirement for dimer splaying in highly curved membranes. These results suggest that the membrane curving activity of DP1 proteins requires both dimer stability and conformational plasticity at the intermolecular interface.