Differential effects of Usp14 and Uch-L1 on the ubiquitin proteasome system and synaptic activity

120

Ubiquitin carboxy-terminal hydrolase L1 (UCHL1) is a Parkinson disease-associated, putative cysteine protease found abundantly and selectively expressed in neurons. The crystal structure of apo UCHL1 showed that the active-site residues are not aligned in a canonical form, with the nucleophilic cysteine being 7.7 Å from the general base histidine, an arrangement consistent with an inactive form of the enzyme. Here we report the crystal structures of the wild type and two Parkinson disease-associated variants of the enzyme, S18Y and I93M, bound to a ubiquitin-based suicide substrate, ubiquitin vinyl methyl ester. These structures reveal that ubiquitin vinyl methyl ester binds primarily at two sites on the enzyme, with its carboxy terminus at the active site and with its amino-terminal β-hairpin at the distal site-a surface-exposed hydrophobic crevice 17 Å away from the active site. Binding at the distal site initiates a cascade of side-chain movements in the enzyme that starts at a highly conserved, surface-exposed phenylalanine and is relayed to the active site resulting in the reorientation and proximal placement of the general base within 4 Å of the catalytic cysteine, an arrangement found in productive cysteine proteases. Mutation of the distal-site, surface-exposed phenylalanine to alanine reduces ubiquitin binding and severely impairs the catalytic activity of the enzyme. These results suggest that the activity of UCHL1 may be regulated by its own substrate.deubiquitinating enzyme | enzyme suicide substrate complex | neurodegeneration | ubiquitination U CHL1, a member of the UCH (ubiquitin C-terminal hydrolase) family of deubiquitinating enzymes (DUBs), is a 223-amino acid protein found abundantly and selectively expressed in brain, constituting up to 1-2% of total brain protein (1, 2). In vivo studies suggest that UCHL1 is involved in regulation of ubiquitin pool, apoptosis, and learning and memory, and its absence in mice because of spontaneous intragenic deletions yields phenotypes with neurological defects (3). Mutations in UCHL1 have been implicated in Parkinson disease (PD). A point mutation near the active site that changes Ile93 to Met (I93M) has been linked to an increased risk of developing an autosomaldominant form of PD (4). Conversely, a common S18Y polymorphism reduces susceptibility to PD (5, 6) and Alzheimer's disease (7). In addition to its association with neurodegenerative diseases, abnormal expression of UCHL1 is found in many forms of cancer, including lung, colorectal, and pancreatic cancers, and may be related to tumor progression (8, 9). The normal function of UCHL1, however, is not known. Also unknown are how the activity of this abundant neuronal enzyme is regulated and what its true physiological substrates are, although biochemical studies have indicated that UCHL1 can accept short-peptide (α or ϵ-amino-linked) or small-molecule C-terminal conjugates of ubiquitin as substrates, cleaving, as its name suggests, the amide bond following immediately after the C-terminal glycine (Gly7...

Section: Al Demonstrating That Leu8 Of Ubiquitin Is Critically Requimentioning

confidence: 80%

Ubiquitin vinyl methyl ester binding orients the misaligned active site of the ubiquitin hydrolase UCHL1 into productive conformation

Boudreaux

Maiti

Davies

et al. 2010

120

“…Vogiatzi et al (49) have reported recently that ␣-synuclein is degraded by both of these pathways in neuroblastoma cells and in primary neurons. Walters et al (7) have suggested that UCH-L1 is involved in a lysosomal pathway.…”

Section: Uch-l1 M Causes Accumulation Of ␣-Synuclein Without Affectinmentioning

confidence: 99%

“…UCH-L1 is robustly expressed in neurons, comprising 1-2% of total brain protein (6), and its absence in mice due to spontaneous intragenic deletions produces neurologic and neurodegenerative phenotypes (1,7). An S18Y polymorphism in UCH-L1 reduces susceptibility to Parkinson's disease (PD) (8)(9)(10)(11)(12)) and Alzheimer's disease (AD) (13) and may influence the age at onset of Huntington's disease (14).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Membrane-associated farnesylated UCH-L1 promotes α-synuclein neurotoxicity and is a therapeutic target for Parkinson's disease

Liu

Meray

Grammatopoulos³

et al. 2009

124

131

Ubiquitin C-terminal hydrolase-L1 (UCH-L1) is linked to Parkinson's disease (PD) and memory and is selectively expressed in neurons at high levels. Its expression pattern suggests a function distinct from that of its widely expressed homolog UCH-L3. We report here that, in contrast to UCH-L3, UCH-L1 exists in a membrane-associated form (UCH-L1 M ) in addition to the commonly studied soluble form. C-terminal farnesylation promotes the association of UCH-L1 with cellular membranes, including the endoplasmic reticulum. The amount of UCH-L1 M in transfected cells is shown to correlate with the intracellular level of ␣-synuclein, a protein whose accumulation is associated with neurotoxicity and the development of PD. Reduction of UCH-L1 M in cell culture models of ␣-synuclein toxicity by treatment with a farnesyltransferase inhibitor (FTI-277) reduces ␣-synuclein levels and increases cell viability. Proteasome function is not affected by UCH-L1 M , suggesting that it may negatively regulate the lysosomal degradation of ␣-synuclein. Therefore, inhibition of UCH-L1 farnesylation may be a therapeutic strategy for slowing the progression of PD and related synucleinopathies.farnesylation ͉ synuclein

“…On one hand, impairment of the maintenance of theta-burst stimulation-induced long-term potentiation (LTP) in hippocampus was reported in gad mice (18). On the other hand, the maintenance of LTP was unaffected in another line of mutant mice carrying a spontaneous deletion of the UCH-L1 gene (nm3419) (19).…”

mentioning

confidence: 99%

Ubiquitin carboxyl-terminal hydrolase L1 is required for maintaining the structure and function of the neuromuscular junction

Chen

Sugiura

Myers

et al. 2010

114

107

The enzyme ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) is one of the most abundant proteins in the mammalian nervous system. In humans, UCH-L1 is also found in the ubiquitinated inclusion bodies that characterize neurodegenerative diseases in the brain, suggesting its involvement in neurodegeneration. The physiologic role of UCH-L1 in neurons, however, remains to be further elucidated. For example, previous studies have provided evidence both for and against the role of UCH-L1 in synaptic function in the brain. Here, we have characterized a line of knockout mice deficient in the UCH-L1 gene. We found that, in the absence of UCH-L1, synaptic transmission at the neuromuscular junctions (NMJs) is markedly impaired. Both spontaneous and evoked synaptic activity are reduced; paired pulse-facilitation is impaired, and synaptic transmission fails to respond to high-frequency, repetitive stimulation at the NMJs of UCH-L1 knockout mice. Morphologic analyses of the NMJs further revealed profound structural defects-loss of synaptic vesicles and accumulation of tubulovesicular structures at the presynaptic nerve terminals, and denervation of the muscles in UCH-L1 knockout mice. These findings demonstrate that UCH-L1 is required for the maintenance of the structure and function of the NMJ and that the loss of normal UCH-L1 activity may result in neurodegeneration in the peripheral nervous system. electrophysiology | knockout mice | neurodegeneration | synaptic transmission