RESUMO
The cytosolic antibody receptor and RING E3 ligase TRIM21 targets intracellular, antibody-coated immune complexes for degradation and activates the immune system. Here we review how TRIM21 degrades diverse targets and how this activity can be exploited in molecular biology and for the development of new therapeutics. In addition, we compare what is known about TRIM21's mechanism to other TRIM proteins and RING E3 ligases.
Assuntos
Ribonucleoproteínas , Ubiquitina-Proteína Ligases , Anticorpos , Citosol/metabolismo , Ribonucleoproteínas/genética , Ribonucleoproteínas/metabolismo , Ubiquitina-Proteína Ligases/metabolismo , UbiquitinaçãoRESUMO
The S. pombe orthologue of the human PAXT connection, Mtl1-Red1 Core (MTREC), is an eleven-subunit complex that targets cryptic unstable transcripts (CUTs) to the nuclear RNA exosome for degradation. It encompasses the canonical poly(A) polymerase Pla1, responsible for polyadenylation of nascent RNA transcripts as part of the cleavage and polyadenylation factor (CPF/CPSF). In this study we identify and characterise the interaction between Pla1 and the MTREC complex core component Red1 and analyse the functional relevance of this interaction in vivo. Our crystal structure of the Pla1-Red1 complex shows that a 58-residue fragment in Red1 binds to the RNA recognition motif domain of Pla1 and tethers it to the MTREC complex. Structure-based Pla1-Red1 interaction mutations show that Pla1, as part of MTREC complex, hyper-adenylates CUTs for their efficient degradation. Interestingly, the Red1-Pla1 interaction is also required for the efficient assembly of the fission yeast facultative heterochromatic islands. Together, our data suggest a complex interplay between the RNA surveillance and 3'-end processing machineries.
Assuntos
Polinucleotídeo Adenililtransferase , Proteínas de Schizosaccharomyces pombe , Schizosaccharomyces , Proteínas de Transporte/metabolismo , Núcleo Celular/metabolismo , Polinucleotídeo Adenililtransferase/genética , Polinucleotídeo Adenililtransferase/metabolismo , RNA/metabolismo , Precursores de RNA/metabolismo , Schizosaccharomyces/genética , Schizosaccharomyces/metabolismo , Proteínas de Schizosaccharomyces pombe/genética , Proteínas de Schizosaccharomyces pombe/metabolismoRESUMO
TRIM proteins are the largest family of E3 ligases in mammals. They include the intracellular antibody receptor TRIM21, which is responsible for mediating targeted protein degradation during Trim-Away. Despite their importance, the ubiquitination mechanism of TRIM ligases has remained elusive. Here we show that while Trim-Away activation results in ubiquitination of both ligase and substrate, ligase ubiquitination is not required for substrate degradation. N-terminal TRIM21 RING ubiquitination by the E2 Ube2W can be inhibited by N-terminal acetylation, but this doesn't prevent substrate ubiquitination nor degradation. Instead, uncoupling ligase and substrate degradation prevents ligase recycling and extends functional persistence in cells. Further, Trim-Away degrades substrates irrespective of whether they contain lysines or are N-terminally acetylated, which may explain the ability of TRIM21 to counteract fast-evolving pathogens and degrade diverse substrates.
Assuntos
Lisina , Ubiquitina-Proteína Ligases , Animais , Lisina/metabolismo , Ubiquitinação , Ubiquitina-Proteína Ligases/genética , Ubiquitina-Proteína Ligases/metabolismo , Processamento de Proteína Pós-Traducional , Proteólise , Mamíferos/metabolismoRESUMO
Attachment of ubiquitin (Ub) to proteins is one of the most abundant and versatile of all posttranslational modifications and affects outcomes in essentially all physiological processes. RING E3 ligases target E2 Ub-conjugating enzymes to the substrate, resulting in its ubiquitination. However, the mechanism by which a ubiquitin chain is formed on the substrate remains elusive. Here we demonstrate how substrate binding can induce a specific RING topology that enables self-ubiquitination. By analyzing a catalytically trapped structure showing the initiation of TRIM21 RING-anchored ubiquitin chain elongation, and in combination with a kinetic study, we illuminate the chemical mechanism of ubiquitin conjugation. Moreover, biochemical and cellular experiments show that the topology found in the structure can be induced by substrate binding. Our results provide insights into ubiquitin chain formation on a structural, biochemical and cellular level with broad implications for targeted protein degradation.
Assuntos
Biocatálise , Domínios RING Finger , Ubiquitinação , Animais , Feminino , Masculino , Camundongos , Modelos Moleculares , Células NIH 3T3 , Proteólise , Ribonucleoproteínas/química , Especificidade por Substrato , Ubiquitina/química , Ubiquitina/metabolismoRESUMO
The COVID-19 pandemic, caused by the SARS-CoV-2 coronavirus, has triggered a worldwide health emergency. Here, we show that ferritin-like Dps from hyperthermophilic Sulfolobus islandicus, covalently coupled with SARS-CoV-2 antigens via the SpyCatcher system, forms stable multivalent dodecameric vaccine nanoparticles that remain intact even after lyophilisation. Immunisation experiments in mice demonstrated that the SARS-CoV-2 receptor binding domain (RBD) coupled to Dps (RBD-S-Dps) elicited a higher antibody titre and an enhanced neutralising antibody response compared to monomeric RBD. A single immunisation with RBD-S-Dps completely protected hACE2-expressing mice from serious illness and led to viral clearance from the lungs upon SARS-CoV-2 infection. Our data highlight that multimerised SARS-CoV-2 subunit vaccines are a highly efficacious modality, particularly when combined with an ultra-stable scaffold.
Assuntos
Enzima de Conversão de Angiotensina 2/imunologia , Vacinas contra COVID-19/imunologia , COVID-19/prevenção & controle , Receptores Virais/imunologia , Glicoproteína da Espícula de Coronavírus/imunologia , Animais , Anticorpos Neutralizantes/imunologia , Anticorpos Antivirais/imunologia , Proteínas de Bactérias/química , Vacinas contra COVID-19/administração & dosagem , Vacinas contra COVID-19/química , Proteínas de Ligação a DNA/química , Ferritinas/química , Humanos , Imunização , Camundongos , Nanopartículas , Domínios Proteicos , Multimerização Proteica , Glicoproteína da Espícula de Coronavírus/química , SulfolobusRESUMO
Trim-Away is a recently developed technology that exploits off-the-shelf antibodies and the RING E3 ligase and cytosolic antibody receptor TRIM21 to carry out rapid protein depletion. How TRIM21 is catalytically activated upon target engagement, either during its normal immune function or when repurposed for targeted protein degradation, is unknown. Here we show that a mechanism of target-induced clustering triggers intermolecular dimerization of the RING domain to switch on the ubiquitination activity of TRIM21 and induce virus neutralization or drive Trim-Away. We harness this mechanism for selective degradation of disease-causing huntingtin protein containing long polyglutamine tracts and expand the Trim-Away toolbox with highly active TRIM21-nanobody chimeras that can also be controlled optogenetically. This work provides a mechanism for cellular activation of TRIM RING ligases and has implications for targeted protein degradation technologies.
Assuntos
Proteólise , Ribonucleoproteínas/metabolismo , Ubiquitinação , Animais , Biocatálise , Linhagem Celular , Drosophila melanogaster/citologia , Humanos , Proteína Huntingtina/química , Proteína Huntingtina/metabolismo , Camundongos , Modelos Moleculares , Optogenética , Peptídeos/metabolismo , Ligação Proteica , Multimerização Proteica , Ribonucleoproteínas/química , Ubiquitina-Proteína Ligases/metabolismoRESUMO
HIV virion assembly begins with the construction of an immature lattice consisting of Gag hexamers. Upon virion release, protease-mediated Gag cleavage leads to a maturation event in which the immature lattice disassembles and the mature capsid assembles. The cellular metabolite inositiol hexakisphosphate (IP6) and maturation inhibitors (MIs) both bind and stabilize immature Gag hexamers, but whereas IP6 promotes virus maturation, MIs inhibit it. Here we show that HIV is evolutionarily constrained to maintain an immature lattice stability that ensures IP6 packaging without preventing maturation. Replication-deficient mutant viruses with reduced IP6 recruitment display increased infectivity upon treatment with the MI PF46396 (PF96) or the acquisition of second-site compensatory mutations. Both PF96 and second-site mutations stabilise the immature lattice and restore IP6 incorporation, suggesting that immature lattice stability and IP6 binding are interdependent. This IP6 dependence suggests that modifying MIs to compete with IP6 for Gag hexamer binding could substantially improve MI antiviral potency.
RESUMO
Rapid COVID-19 diagnosis in the hospital is essential, although this is complicated by 30%-50% of nose/throat swabs being negative by SARS-CoV-2 nucleic acid amplification testing (NAAT). Furthermore, the D614G spike mutant dominates the pandemic and it is unclear how serological tests designed to detect anti-spike antibodies perform against this variant. We assess the diagnostic accuracy of combined rapid antibody point of care (POC) and nucleic acid assays for suspected COVID-19 disease due to either wild-type or the D614G spike mutant SARS-CoV-2. The overall detection rate for COVID-19 is 79.2% (95% CI 57.8-92.9) by rapid NAAT alone. The combined point of care antibody test and rapid NAAT is not affected by D614G and results in very high sensitivity for COVID-19 diagnosis with very high specificity.
Assuntos
Teste para COVID-19/métodos , COVID-19/diagnóstico , Testes Imediatos , SARS-CoV-2/isolamento & purificação , Idoso , Idoso de 80 Anos ou mais , Anticorpos Antivirais/sangue , Teste para COVID-19/normas , Feminino , Humanos , Imunoensaio , Masculino , Pessoa de Meia-Idade , Testes de Neutralização , Técnicas de Amplificação de Ácido Nucleico , SARS-CoV-2/genética , SARS-CoV-2/imunologia , Sensibilidade e Especificidade , Glicoproteína da Espícula de Coronavírus/genética , Glicoproteína da Espícula de Coronavírus/imunologiaRESUMO
The cytosolic antibody receptor TRIM21 possesses unique ubiquitination activity that drives broad-spectrum anti-pathogen targeting and underpins the protein depletion technology Trim-Away. This activity is dependent on formation of self-anchored, K63-linked ubiquitin chains by the heterodimeric E2 enzyme Ube2N/Ube2V2. Here we reveal how TRIM21 facilitates ubiquitin transfer and differentiates this E2 from other closely related enzymes. A tri-ionic motif provides optimally distributed anchor points that allow TRIM21 to wrap an Ube2N~Ub complex around its RING domain, locking the closed conformation and promoting ubiquitin discharge. Mutation of these anchor points inhibits ubiquitination with Ube2N/Ube2V2, viral neutralization and immune signalling. We show that the same mechanism is employed by the anti-HIV restriction factor TRIM5 and identify spatially conserved ionic anchor points in other Ube2N-recruiting RING E3s. The tri-ionic motif is exclusively required for Ube2N but not Ube2D1 activity and provides a generic E2-specific catalysis mechanism for RING E3s.
Assuntos
Lisina/metabolismo , Ribonucleoproteínas/metabolismo , Enzimas de Conjugação de Ubiquitina/metabolismo , Ubiquitinação/fisiologia , Motivos de Aminoácidos/genética , Fatores de Restrição Antivirais , Biocatálise , Cristalografia por Raios X , Células HEK293 , Células HeLa , Humanos , Modelos Moleculares , Mutação , Ressonância Magnética Nuclear Biomolecular , Ligação Proteica/genética , Ribonucleoproteínas/química , Ribonucleoproteínas/genética , Proteínas com Motivo Tripartido/metabolismo , Ubiquitina/metabolismo , Enzimas de Conjugação de Ubiquitina/química , Ubiquitina-Proteína Ligases/metabolismoRESUMO
Ras homolog enriched in brain (Rheb) is a small GTPase that regulates mammalian/mechanistic target of rapamycin complex 1 (mTORC1) and, thereby, cell growth and metabolism. Here we show that cycling between the inactive GDP- and the active GTP-bound state modulates the backbone dynamics of a C-terminal truncated form, RhebΔCT, which is suggested to influence its interactions. We further investigated the interactions between RhebΔCT and the proposed Rheb-binding domain of the regulatory protein FKBP38. The observed weak interactions with the GTP-analogue- (GppNHp-) but not the GDP-bound state, appear to accelerate the GDP to GTP exchange, but only very weakly compared to a genuine GEF. Thus, FKBP38 is most likely not a GEF but a Rheb effector that may function in membrane targeting of Rheb.