Structural basis for the recognition of Lys48-linked polyubiquitin chain by the Josephin domain of ataxin-3, a putative deubiquitinating enzyme
[ATX3_HUMAN] Defects in ATXN3 are the cause of spinocerebellar ataxia type 3 (SCA3) [MIM:109150]; also known as Machado-Joseph disease (MJD). Spinocerebellar ataxia is a clinically and genetically heterogeneous group of cerebellar disorders. Patients show progressive incoordination of gait and often poor coordination of hands, speech and eye movements, due to degeneration of the cerebellum with variable involvement of the brainstem and spinal cord. SCA3 belongs to the autosomal dominant cerebellar ataxias type I (ADCA I) which are characterized by cerebellar ataxia in combination with additional clinical features like optic atrophy, ophthalmoplegia, bulbar and extrapyramidal signs, peripheral neuropathy and dementia. The molecular defect in SCA3 is the a CAG repeat expansion in ATXN3 coding region. Longer expansions result in earlier onset and more severe clinical manifestations of the disease.
[ATX3_HUMAN] Deubiquitinating enzyme involved in protein homeostasis maintenance, transcription, cytoskeleton regulation, myogenesis and degradation of misfolded chaperone substrates. Binds long polyubiquitin chains and trims them, while it has weak or no activity against chains of 4 or less ubiquitins. Involved in degradation of misfolded chaperone substrates via its interaction with STUB1/CHIP: recruited to monoubiquitinated STUB1/CHIP, and restricts the length of ubiquitin chain attached to STUB1/CHIP substrates and preventing further chain extension. In response to misfolded substrate ubiquitination, mediates deubiquitination of monoubiquitinated STUB1/CHIP. Interacts with key regulators of transcription and represses transcription: acts as a histone-binding protein that regulates transcription.  
Publication Abstract from PubMed
Ataxin-3, which is encoded by a gene that has been associated with Machado-Joseph disease, contains a catalytic N-terminal Josephin domain with deubiquitinase activity. Here, we show that the Josephin domain of ataxin 3 catalyzes endo-type cleavage of Lys48-linked polyubiquitin. Furthermore, NMR data obtained following site-specific paramagnetic spin labeling of Lys48-linked di-ubiquitin revealed that both ubiquitin units interact with the Josephin domain, with the C-terminal Gly76 of the proximal unit being situated in the vicinity of the catalytic triad of Josephin domain. Our results help to elucidate how the substrate is recognized by the Josephin domain and properly positioned for an endo-type deubiquitination reaction.
Mode of substrate recognition by the Josephin domain of ataxin-3, which has an endo-type deubiquitinase activity.,Satoh T, Sumiyoshi A, Yagi-Utsumi M, Sakata E, Sasakawa H, Kurimoto E, Yamaguchi Y, Li W, Joazeiro CA, Hirokawa T, Kato K FEBS Lett. 2014 Nov 28;588(23):4422-30. doi: 10.1016/j.febslet.2014.10.013. Epub , 2014 Oct 19. PMID:25448680
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.