RESUMEN
K11/K48-branched ubiquitin chains are proteasomal priority signals that elicit the rapid elimination of mitotic regulators and aggregation-prone proteins. Indicative of an intriguing signaling mode, Boughton et al. (2019) unravel an interaction between distal subunits of K11/K48-branched ubiquitin trimers that could provide a combined surface for recognition by the proteasomal receptor RPN1.
Asunto(s)
Complejo de la Endopetidasa Proteasomal , Ubiquitina , Proteínas Portadoras , Transducción de Señal , UbiquitinaciónRESUMEN
Metazoan development depends on tightly regulated gene expression programs that instruct progenitor cells to adopt specialized fates. Recent work found that posttranslational modifications, such as monoubiquitylation, can determine cell fate also independently of effects on transcription, yet how monoubiquitylation is implemented during development is poorly understood. Here, we have identified a regulatory circuit that controls monoubiquitylation-dependent neural crest specification by the E3 ligase CUL3 and its substrate adaptor KBTBD8. We found that CUL3KBTBD8 monoubiquitylates its essential targets only after these have been phosphorylated in multiple motifs by CK2, a kinase whose levels gradually increase during embryogenesis. Its dependency on multisite phosphorylation allows CUL3KBTBD8 to convert the slow rise in embryonic CK2 into decisive recognition of ubiquitylation substrates, which in turn is essential for neural crest specification. We conclude that multisite dependency of an E3 ligase provides a powerful mechanism for switch-like cell fate transitions controlled by monoubiquitylation.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales/metabolismo , Diferenciación Celular , Proteínas Cullin/metabolismo , Células Madre Embrionarias Humanas/fisiología , Ubiquitinación , Quinasa de la Caseína II/metabolismo , Células Cultivadas , Humanos , Fosforilación , Procesamiento Proteico-PostraduccionalRESUMEN
Selective inhibition of the immunoproteasome is a promising approach towards the development of immunomodulatory drugs. Recently, a class of substituted thiazole compounds that combine a nonpeptidic scaffold with the absence of an electrophile was reported in a patent. Here, we investigated the mode of action of the lead compound by using a sophisticated chimeric yeast model of the human immunoproteasome for structural studies. The inhibitor adopts a unique orientation perpendicular to the ß5i substrate-binding channel. Distinct interactions between the inhibitor and the subpockets of the human immunoproteasome account for its isotype selectivity.
Asunto(s)
Factores Inmunológicos/química , Modelos Moleculares , Oligopéptidos/química , Complejo de la Endopetidasa Proteasomal/química , Inhibidores de Proteasoma/química , Humanos , Estructura Molecular , Péptidos/química , Complejo de la Endopetidasa Proteasomal/efectos de los fármacos , Complejo de la Endopetidasa Proteasomal/metabolismoRESUMEN
Clinically applied proteasome inhibitors induce cell death by concomitant blockage of constitutive and immunoproteasomes. In contrast, selective immunoproteasome inhibition is less cytotoxic and has the potential to modulate chronic inflammation and autoimmune diseases. In this study, we rationally designed decarboxylated peptides that covalently target a non-catalytic cysteine of the immunoproteasome subunit ß5i with α-chloroacetamide-containing sidechains. The enhanced isoform specificity decreased cytotoxic effects and the compound suppressed the production of inflammatory cytokines. Structure-based optimization led to over 150-fold selectivity for subunit ß5i over ß5c. This new compound class provides a promising starting point for the development of selective immunoproteasome inhibitors as potential anti-inflammatory agents.