title: Novel UCHL1 mutations reveal new insights into ubiquitin processing.
abstract: Recessive loss of function of the neuronal ubiquitin hydrolase UCHL1 has been implicated in early-onset progressive neurodegeneration (MIM no. 615491), so far only in one family. In this study a second family is characterized, and the functional consequences of the identified mutations in UCHL1 are explored. Three siblings developed childhood-onset optic atrophy, followed by spasticity and ataxia. Whole exome sequencing identified compound heterozygous variants in UCHL1, c.533G > A (p.Arg178Gln) and c.647C > A (p.Ala216Asp), cosegregating with the phenotype. Enzymatic activity of purified recombinant proteins analysed by ubiquitin hydrolase assays showed a 4-fold increased hydrolytic activity of the recombinant UCHL1 mutant Arg178Gln compared to wild type, whereas the Ala216Asp protein was insoluble. Structural 3D analysis of UCHL1 by computer modelling suggests that Arg178 is a rate-controlling residue in catalysis which is partly abolished in the Arg178Gln mutant and, consequently, the Arg178Gln mutant increases the enzymatic turnover. UCHL1 protein levels in fibroblasts measured by targeted mass spectrometry showed a total amount of UCHL1 in control fibroblasts about 4-fold higher than in the patients. Hence, studies of the identified missense variants reveal surprisingly different functional consequences as the insoluble Ala216Asp variant leads to loss of function, whereas the Arg178Gln leads to increased enzyme activity. The reported patients have remarkably preserved cognition, and we propose that the increased enzyme activity of the Arg178Gln variant offers a protective effect on cognitive function. This study establishes the importance of UCHL1 in neurodegeneration, provides new mechanistic insight about ubiquitin processing, and underlines the complexity of the different roles of UCHL1.
authors.affiliation: Department of Neurology, Oslo University Hospital, Norway.|Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Norway.
authors.forename: Siri L
authors.initials: SL
authors.lastname: Rydning
authors.affiliation: Department of Microbiology, Oslo University Hospital, Norway.|Department of Medical Biochemistry, University of Oslo, Norway.
authors.forename: Paul H
authors.initials: PH
authors.lastname: Backe
authors.affiliation: Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
authors.forename: Mirta M L
authors.initials: MML
authors.lastname: Sousa
authors.affiliation: Department of Neurology, Oslo University Hospital, Norway.
authors.forename: Zafar
authors.initials: Z
authors.lastname: Iqbal
authors.affiliation: Department of Medical Genetics, Oslo University Hospital and University of Oslo, Norway.
authors.forename: Ane-Marte
authors.initials: AM
authors.lastname: Øye
authors.affiliation: Department of Medical Genetics, Oslo University Hospital and University of Oslo, Norway.
authors.forename: Ying
authors.initials: Y
authors.lastname: Sheng
authors.affiliation: Department of Microbiology, Oslo University Hospital, Norway.|Department of Medical Biochemistry, University of Oslo, Norway.
authors.forename: Mingyi
authors.initials: M
authors.lastname: Yang
authors.affiliation: Department of Microbiology, Oslo University Hospital, Norway.|Department of Medical Biochemistry, University of Oslo, Norway.
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Lin
authors.affiliation: Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.|Proteomics and Metabolomics Core Facility (PROMEC), NTNU, Trondheim, Norway.
authors.forename: Geir
authors.initials: G
authors.lastname: Slupphaug
authors.affiliation: Department of Physical Medicine and Rehabilitation, Oslo University Hospital, Norway.
authors.forename: Tonje H
authors.initials: TH
authors.lastname: Nordenmark
authors.affiliation: Department of Medical Genetics, Oslo University Hospital and University of Oslo, Norway.
authors.forename: Magnus D
authors.initials: MD
authors.lastname: Vigeland
authors.affiliation: Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Norway.|Department of Microbiology, Oslo University Hospital, Norway.|Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
authors.forename: Magnar
authors.initials: M
authors.lastname: Bjørås
authors.affiliation: Department of Neurology, Oslo University Hospital, Norway.|Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Norway.
authors.forename: Chantal M
authors.initials: CM
authors.lastname: Tallaksen
authors.affiliation: Department of Medical Genetics, Oslo University Hospital and University of Oslo, Norway.
authors.forename: Kaja K
authors.initials: KK
authors.lastname: Selmer
mesh_terms: D000368:Aged; D000818:Animals; D001259:Ataxia / Q000000981:diagnostic imaging / Q000235:genetics* / Q000503:physiopathology; D004195:Disease Models, Animal; D059472:Exome; D005260:Female; D006579:Heterozygote; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D009410:Nerve Degeneration / Q000000981:diagnostic imaging / Q000235:genetics* / Q000503:physiopathology; D009896:Optic Atrophy / Q000000981:diagnostic imaging / Q000235:genetics* / Q000503:physiopathology; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics*; D035781:Siblings; D013329:Structure-Activity Relationship; D043222:Ubiquitin Thiolesterase / Q000737:chemistry / Q000235:genetics*
chemical_list: D011994:Recombinant Proteins; C482860:UCHL1 protein, human; D043222:Ubiquitin Thiolesterase