The Ubiquitin-conjugating Enzymes UbcH7 and UbcH8 Interact with RING Finger/IBR Motif-containing Domains of HHARI and H7-AP1

907

744

P arkinson's disease (PD) is the second most prevalent neurodegenerative disorder, but the etiology remains poorly understood (1, 2). Patients with PD suffer from rigidity, slowness of movement, tremor, and disturbances of balance (1, 2). PD is characterized by the progressive loss of dopamine-containing neurons in the substantia nigra pars compacta (3, 4) and the accumulation of Lewy bodies, proteinaceous intracytoplasmic accumulations of eosinophilic material that stain for ubiquitin (5). Novel insights into the molecular mechanisms of the pathogenesis of PD have come from the identification of genes associated with rare forms of familial PD (6). Mutations in ␣-synuclein (A53T and A30P) are linked to autosomal dominant PD (7,8). This led to the discovery that ␣-synuclein is a major component of Lewy bodies and suggests that derangements in ␣-synuclein could be a major cause or contributor to the pathogenesis of sporadic PD (9, 10). Consistent with this notion are observations that overexpression of ␣-synuclein in transgenic fruit flies and mice causes a Parkinsonian phenotype and replicates many of the pathological features of PD (11-13).Other autosomal dominant genes or loci linked to PD have been described and include a mutation (I93M) in ubiquitin carboxyl-terminal-hydrolase-L1 (14), a member of the ubiquitin C-terminal hydrolase family that hydrolyzes small C-terminal adducts of ubiquitin to generate ubiquitin monomers and is involved in facilitating the degradation and processing of proteins through the 26 S proteasome. Thus, derangements in ubiquitin processing may be linked to the pathogenesis of PD. Linkages to chromosome 2P and 4P have been described, as well as yet to be identified loci, but the genes await identification (15-17).Mutations in the Parkin gene are responsible for autosomal recessive PD (18). Several Parkin-associated pedigrees have been described with both deletions and point mutations, as well as compound heterozygosity causing autosomal recessive PD (19)(20)(21). Recent studies suggest that mutations in Parkin are the major cause of autosomal recessive familial PD (19); thus, understanding the function of Parkin and how mutations interfere with the function of Parkin may provide novel insights into the pathogenesis of PD. The function of the Parkin protein remains unknown. However, Parkin shows mild homology to ubiquitin at the N terminus and contains two ring-finger motifs and an in-between ring-finger (IBR) domain at the C terminus (22). Recently, a few proteins with ring-finger motifs similar to Parkin were shown to be involved in E2-dependent ubiquitination (23-26). Ubiquitination requires the ATP-dependent activation of ubiquitin by the ubiquitin-activating enzyme E1. Ubiquitin is transferred to an E2 ubiquitin-conjugating enzyme, which works in conjunction with an E3 ubiquitin-protein ligase to ubiquitinate substrate proteins (23,24). The existence of two ring-finger motifs and the N-terminal homology to ubiquitin suggests that Parkin may be involved in the ubiquitination pathw...

Section: Resultsmentioning

confidence: 99%

Parkin functions as an E2-dependent ubiquitin– protein ligase and promotes the degradation of the synaptic vesicle-associated protein, CDCrel-1

Zhang

Gao

Chung

et al. 2000

907

744

“…To gain further insight into the function and regulation of ISG15 conjugation, we sought here to identify the E2 enzyme that functions in ISG15 conjugation. Surprisingly, we found that UbcH8, an E2 that functions in Ub conjugation pathways (16)(17)(18)(19)(20)(21)(22), is a major E2 enzyme for the ISG15 conjugation pathway. Therefore, our results indicate that the ISG15 conjugation pathway overlaps or converges with the Ub conjugation pathway at the level of a specific E2 enzyme.…”

mentioning

confidence: 94%

“…UbcH8 has been reported to function as an E2 for several Ub E3 enzymes, including both HECT E3s (16) and RING E3s (17)(18)(19)(20)(21)(22). As an initial test of this hypothesis, we determined whether a UbcH8-competent Ub E3 was capable of conjugating ISG15 to a substrate protein in vitro.…”

Section: Isg15mentioning

confidence: 99%

“…The rationale of incorporating UbcH8 into the ISG15 conjugation pathway in this model might be to take advantage of a preexisting set of E3s and switch them from performing Ub conjugation to ISG15 conjugation. Candidate E3s in this model include both HECT and single-subunit RING E3s, which are so far the only families of E3s that contain members capable of using UbcH8 (16)(17)(18)(19)(20)(21)(22) and possibly those E3s that interact with the closely related E2 UbcH7.…”

Section: Isg15mentioning

confidence: 99%

See 1 more Smart Citation

The UbcH8 ubiquitin E2 enzyme is also the E2 enzyme for ISG15, an IFN-α/β-induced ubiquitin-like protein

Zhao

Beaudenon

Kelley

et al. 2004

280

211

Ubiquitin-(Ub) like proteins (Ubls) are conjugated to their targets by an enzymatic cascade involving an E1 activating enzyme, an E2 conjugating enzyme, and in some cases an E3 ligase. ISG15 is a Ubl that is conjugated to cellular proteins after IFN-␣͞␤ stimulation. Although the E1 enzyme for ISG15 (Ube1L͞E1 ISG15 ) has been identified, the identities of the downstream components of the ISG15 conjugation cascade have remained elusive. Here we report the purification of an E2 enzyme for ISG15 and demonstrate that it is UbcH8, an E2 that also functions in Ub conjugation. In vitro assays with purified Ub E2 enzymes and in vivo RNA interference assays indicate that UbcH8 is a major E2 enzyme for ISG15 conjugation. These results indicate that the ISG15 conjugation pathway overlaps or converges with the Ub conjugation pathway at the level of a specific E2 enzyme. Furthermore, these results raise the possibility that the ISG15 conjugation pathway might use UbcH8-competent Ub ligases in vivo. As an initial test of this hypothesis, we have shown that a UbcH8-competent Ub ligase conjugates ISG15 to a specific target in vitro. These results challenge the concept that Ub and Ubl conjugation pathways are strictly parallel and nonoverlapping and have important implications for understanding the regulation and function of ISG15 conjugation in the IFN-␣͞␤ response. IFN-␣͞␤ play an essential role in innate immunity and are induced during many types of viral infections (1). Many genes are transcriptionally induced by IFN-␣͞␤, including ISG15 (IFNstimulated gene, 15 kDa) (2, 3). The ISG15 protein is a 15-kDa ubiquitin (Ub)-like protein (Ubl), consisting of two Ub-related domains, Ϸ30% (N-terminal domain) and 36% (C-terminal domain) identical to Ub. ISG15 becomes conjugated to a diverse set of cellular proteins after IFN-␣͞␤ stimulation (4). Although the biochemical consequences of ISG15 conjugation and the fate of the conjugated proteins are not known, it does not appear that ISG15 targets proteins for proteasomal degradation (5, 6).Conjugation of Ub to target proteins requires the cooperative activities of at least three classes of enzymes (7). The ATPdependent E1 enzyme activates Ub by C-terminal adenylation, followed by formation of a high-energy thioester bond between the terminal carboxylate of Ub and the active-site cysteine of E1. Ub is then transferred to the active-site cysteine of one of a number of related E2 enzymes. E3 enzymes then promote transfer of Ub from the E2 to the substrate, resulting in a stable amide bond between -amino groups of lysine side chains and Ub. E3 enzymes are the primary determinants of substrate specificity and can be divided into two classes based on mechanism. HECT E3s accept Ub from the E2 enzyme, again in the form of a thioester adduct, and transfer Ub from their active-site cysteine to the bound substrate (8). RING E3s consist of several subclasses and are either single or multisubunit enzymes that serve as docking proteins for both protein substrates and activated E2 enzymes, with transfe...

“…In addition to stabilizing and perhaps controlling E2 and substrate interactions, the IBR domain is required to maintain proper RBR domain geometry crucial in recruiting the chaperone Hsp70 (15), a necessary component in many ubiquitination complexes for the presentation of unfolded substrates. In vitro studies with the RBR E3 ligase HHARI have found that UbcH7 binding and subsequent ubiquitination requires both the RING1 domain and the Nterminal portion of the IBR (16).…”

Section: P Arkinson's Disease (Pd) Is a Common Neurodegenerativementioning

confidence: 99%

Structure of the Parkin in-between-ring domain provides insights for E3-ligase dysfunction in autosomal recessive Parkinson's disease

Beasley

Hristova

Shaw

2007

Mutations in Parkin are one of the predominant hereditary factors found in patients suffering from autosomal recessive juvenile Parkinsonism. Parkin is a member of the E3 ubiquitin ligase family that is defined by a tripartite RING1-in-between-ring (IBR)-RING2 motif. In Parkin, the IBR domain has been shown to augment binding of the E2 proteins UbcH7 and UbcH8, and the subsequent ubiquitination of the proteins synphilin-1, Sept5, and SIM2. To facilitate our understanding of Parkin function, the solution structure of the Parkin IBR domain was solved by using NMR spectroscopy. Folding of the IBR domain (residues M327-S378) was found to be zinc dependent, and the structure reveals the domain forms a unique pair scissor-like and GAG knuckle-like zinc-binding sites, different from other zinc-binding motifs such as the RING, LIM, PHD, or B-box motifs. The N terminus of the IBR domain, residues E307-E322, is unstructured. The disease causing mutation T351P causes global unfolding, whereas the mutation R334C causes some structural rearrangement of the domain. In contrast, the protein containing the mutation G328E appears to be properly folded. The structure of the Parkin IBR domain, in combination with mutational data, allows a model to be proposed where the IBR domain facilitates a close arrangement of the adjacent RING1 and RING2 domains to facilitate protein interactions and subsequent ubiquitination.ubiquitination ͉ zinc-binding ͉ NMR spectroscopy ͉ protein folding ͉ protein interactions P arkinson's disease (PD) is a common neurodegenerative disease characterized by damage to the dopaminergic neurons of the substantia nigra of the midbrain manifesting itself with symptoms such as tremors, rigidity, and bradykinesia (1, 2). Autosomal recessive juvenile PD (ARJP) is an early-onset (Ͻ40 years of age) form of the disease that is caused by hereditary factors including mutations in the genes DJ-1, PINK1, and in about half of the cases, parkin. The protein Parkin has been identified as an E3 ubiquitin-protein ligase of the ubiquitin-proteosome system that is required to maintain cellular protein quality control by removing misfolded or damaged proteins (3, 4). Ubiquitin mediated proteolysis occurs through a cascade of ubiquitin transfers from an E1 activating enzyme, to an E2 conjugating enzyme and finally in complex with an E3 ligase to the target substrate (5, 6). At least 40 different missense and deletion mutations in the parkin gene have been identified and correlated to dysfunction of the ubiquitination system, manifesting itself as ARJP due to the loss of the dopaminergic neurons (7).Parkin is a 465-residue protein comprising an N-terminal ubiquitin-like domain, a unique Parkin-specific domain in the central region, and two RING finger domains (RING1, RING2) separated by an in-between ring (IBR) or double ring linked domain near its C terminus. The cysteine and histidine rich RING-IBR-RING (RBR) domain architecture is highly conserved and found only in eukaryotes. To date, all characterized proteins containing the ...