RESUMO
Arginine/lysine-rich motifs typically function as targeting signals for the translocation of proteins to the nucleus. Here, we demonstrate that such a motif consisting of four basic amino acids in the polyglutamine protein ataxin-3 (Atx-3) serves as a recognition site for the interaction with the molecular chaperone VCP. Through this interaction, VCP modulates the fibrillogenesis of pathogenic forms of Atx-3 in a concentration-dependent manner, with low concentrations of VCP stimulating fibrillogenesis and excess concentrations suppressing it. No such effect was observed with a mutant Atx-3 variant, which does not contain a functional VCP interaction motif. Strikingly, a stretch of four basic amino acids in the ubiquitin chain assembly factor E4B was also discovered to be critical for VCP binding, indicating that arginine/lysine-rich motifs might be generally utilized by VCP for the targeting of proteins. In vivo studies with Drosophila models confirmed that VCP selectively modulates aggregation and neurotoxicity induced by pathogenic Atx-3. Together, these results define the VCP-Atx-3 association as a potential target for therapeutic intervention and suggest that it might influence the progression of spinocerebellar ataxia type 3.
Assuntos
Arginina/genética , Encéfalo/metabolismo , Proteínas de Ciclo Celular/metabolismo , Lisina/genética , Proteínas do Tecido Nervoso/metabolismo , Adenosina Trifosfatases , Trifosfato de Adenosina/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Animais , Ataxina-3 , Encéfalo/patologia , Células COS , Proteínas de Ciclo Celular/genética , Chlorocebus aethiops , Drosophila/citologia , Drosophila/genética , Drosophila/metabolismo , Proteína Huntingtina , Corpos de Inclusão/metabolismo , Dados de Sequência Molecular , Mutação , Proteínas do Tecido Nervoso/genética , Neurônios/citologia , Neurônios/metabolismo , Sinais de Localização Nuclear/fisiologia , Proteínas Nucleares/metabolismo , Células Fotorreceptoras de Invertebrados/metabolismo , Ligação Proteica , Proteínas Repressoras , Homologia de Sequência de Aminoácidos , Proteína com ValosinaRESUMO
Advances in understanding how GroEL binds to non-native proteins are reported. Conformational flexibility in the GroEL apical domain, which could account for the variety of substrates that GroEL binds, is illustrated by comparison of several independent crystallographic structures of apical domain constructs that show conformational plasticity in helices H and I. Additionally, ESI-MS indicates that apical domain constructs have co-populated conformations at neutral pH. To assess the ability of different apical domain conformers to bind co-chaperone and substrate, model peptides corresponding to the mobile loop of GroES and to helix D from rhodanese were studied. Analysis of apical domain-peptide complexes by ESI-MS indicates that only the folded or partially folded apical domain conformations form complexes that survive gas phase conditions. Fluorescence binding studies show that the apical domain can fully bind both peptides independently. No competition for binding was observed, suggesting the peptides have distinct apical domain-binding sites. Blocking the GroES-apical domain-binding site in GroEL rendered the chaperonin inactive in binding GroES and in assisting the folding of denatured rhodanese, but still capable of binding non-native proteins, supporting the conclusion that GroES and substrate proteins have, at least partially, distinct binding sites even in the intact GroEL tetradecamer.
