Arresting a Torsin ATPase Reshapes the Endoplasmic Reticulum

Rose, April E.; Zhao, Chenguang; Turner, Elizabeth M.; Steyer, Anna M.; Schlieker, Christian

doi:10.1074/jbc.m113.515791

Cited by 35 publications

(56 citation statements)

References 39 publications

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“…We further showed that this equivalent Torsin-activator interface exists with LULL1 as well (Fig. 3E), consistent with our previous data for LULL1 and TorB (24). All in all, these cross-linking experiments faithfully recapitulate the previously established nucleotide dependency of the cofactor interaction, as well as its disruption by the ΔE mutation (3,4,21).…”

Section: Significancesupporting

confidence: 91%

“…3 C-E and Fig. S5) and is in excellent agreement with all previously published mutagenesis and activity data (24)…”

Section: Significancesupporting

confidence: 91%

“…finding that residues at the extreme C terminus of TorB are required for cofactor interaction, membrane remodeling, and ATPase stimulation (24). According to our model, these residues constitute the C-terminal alpha-helix (denoted by an arrowhead in Fig.…”

Section: Significancementioning

confidence: 79%

“…Apart from providing a structural rationale for Torsin activation, our experimental validation of the activator interface between cofactors and TorA (24) (Fig. 3 and Fig.…”

Section: Discussionmentioning

confidence: 99%

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The mechanism of Torsin ATPase activation

Brown

Zhao

Chase

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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146

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Torsins are membrane-associated ATPases whose activity is dependent on two activating cofactors, lamina-associated polypeptide 1 (LAP1) and luminal domain-like LAP1 (LULL1). The mechanism by which these cofactors regulate Torsin activity has so far remained elusive. In this study, we identify a conserved domain in these activators that is predicted to adopt a fold resembling an AAA+ (ATPase associated with a variety of cellular activities) domain. Within these domains, a strictly conserved Arg residue present in both activating cofactors, but notably missing in Torsins, aligns with a key catalytic Arg found in AAA+ proteins. We demonstrate that cofactors and Torsins associate to form heterooligomeric assemblies with a defined Torsin-activator interface. In this arrangement, the highly conserved Arg residue present in either cofactor comes into close proximity with the nucleotide bound in the neighboring Torsin subunit. Because this invariant Arg is strictly required to stimulate Torsin ATPase activity but is dispensable for Torsin binding, we propose that LAP1 and LULL1 regulate Torsin ATPase activity through an active site complementation mechanism.DYT1 dystonia | nuclear envelope | ATPase | Torsin T orsin ATPases belong to the AAA+ (ATPase associated with a variety of cellular activities) superfamily of ATPases (1) but are unusual in that they lack conserved catalytic residues that are typically found in related ATPases (2, 3). Accordingly, Torsins do not display ATPase activity unless they are engaged by their regulatory cofactors lamina-associated polypeptide 1 (LAP1) or luminal domain-like LAP1 (LULL1) (4), which are type II transmembrane proteins residing in the nuclear envelope and endoplasmic reticulum (ER) (5, 6). This property stands in sharp contrast to the behavior of closely related Clp/Hsp100 ATPases, which display considerable basal ATPase activities that are moderately stimulated by their substrates (7,8). Although a number of Clp/Hsp100 proteins use distinct cofactors that confer substrate specificity to the typically hexameric ATPase ring, they operate via similar principles (9). Substrates ultimately engage the pore at the center of the oligomeric assembly. This narrow annulus is defined by pore loops that emanate from each subunit and harbor a conserved aromatic residue that defines the center of the pore (10). The energy of ATP hydrolysis is invested in threading the substrate through this axial channel, and the substrate is unfolded in the process (11).Much less is known about the mode of action of Torsin ATPases, although it is clear that regulation of Torsin activity is of vital importance in an organismal context. A mutation in TorsinA (TorA) causing the movement disorder primary dystonia (12) renders TorA unresponsive to its binding partners LAP1 and LULL1 (4), and a homozygous "knock-in" of this disease allele in mice causes a lethal phenotype, as does a TorA KO (13). A conditional deletion of TorA from the CNS in mice accurately replicates the symptoms of primary dystonia (14). In add...

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Section: Significancesupporting

confidence: 91%

“…3 C-E and Fig. S5) and is in excellent agreement with all previously published mutagenesis and activity data (24)…”

Section: Significancesupporting

confidence: 91%

Section: Significancementioning

confidence: 79%

“…Apart from providing a structural rationale for Torsin activation, our experimental validation of the activator interface between cofactors and TorA (24) (Fig. 3 and Fig.…”

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

The mechanism of Torsin ATPase activation

Brown

Zhao

Chase

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

146

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“…For transient expression, plasmids were transfected into HEK 293T cells using Lipofectamine TM 2000 (Life Technologies). Experiments were performed 24 h post-transfection as described previously (20), unless otherwise specified.…”

Section: Methodsmentioning

confidence: 99%

Site-specific Proteolysis Mobilizes TorsinA from the Membrane of the Endoplasmic Reticulum (ER) in Response to ER Stress and B Cell Stimulation

Zhao

Brown

Tang

et al. 2016

Journal of Biological Chemistry

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Torsin ATPases are the only representatives of the AAA؉ ATPase family that reside in the lumen of the endoplasmic reticulum (ER) and nuclear envelope. Two of these, TorsinA and TorsinB, are anchored to the ER membrane by virtue of an N-terminal hydrophobic domain. Here we demonstrate that the imposition of ER stress leads to a proteolytic cleavage event that selectively removes the hydrophobic domain from the AAA؉ domain of TorsinA, which retains catalytic activity. Both the pharmacological inhibition profile and the identified cleavage site between two juxtaposed cysteine residues are distinct from those of presently known proteases, suggesting that a hitherto uncharacterized, membrane-associated protease accounts for TorsinA processing. This processing occurs not only in stressexposed cell lines but also in primary cells from distinct organisms including stimulated B cells, indicating that Torsin conversion in response to physiologically relevant stimuli is an evolutionarily conserved process. By establishing 5-nitroisatin as a cell-permeable inhibitor for Torsin processing, we provide the methodological framework for interfering with Torsin processing in a wide range of primary cells without the need for genetic manipulation.The human genome encodes four Torsin ATPases (TorsinA, TorsinB, Torsin 2A, and Torsin3A), all of which are members of the ATPases associated with a variety of cellular activities (AAAϩ) 3 family (1, 2). Of those, TorsinA is the best characterized Torsin ATPase due to its association with the congenital movement disorder DYT1 dystonia (3). TorsinA has been implicated in a variety of cellular processes, including protein quality control and cellular stress responses (4 -9), although its precise mechanistic functions remain to be identified (2, 10). Although Torsins are phylogenetically closely related to Clp/ HSP100 proteins, they are characterized by a number of atypical features (for a recent review, see Refs. 2 and 10). On the primary structural level, these include differences in the Walker A motif responsible for nucleotide binding, as well as the absence of an otherwise conserved arginine residue required for ATP hydrolysis (10).TorsinA is directed to the lumen of the endoplasmic reticulum by a cleavable N-terminal signal sequence, which is followed by a hydrophobic domain responsible for membrane anchoring and ER retention (11). TorsinA is partitioned between the ER and the contiguous perinuclear space of the nuclear envelope, and its localization is controlled in part by its association with LAP1 and LULL1, type II transmembrane proteins residing in the nuclear envelope and ER, respectively (12)(13)(14). Another unusual property of Torsins is that they lack significant basal ATPase activity in isolation and are tightly regulated by LAP1 and LULL1, which integrate into the Torsin ring via AAA-like domains to trigger ATP hydrolysis through an active site complementation mechanism (15-17). Thus, Torsins and their ATPase activating cofactors form a composite, membrane-spanning assembly....

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Biochemical and Cellular Analysis of Human Variants of the DYT1 Dystonia Protein, TorsinA/TOR1A

et al. 2014

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Early-onset dystonia is associated with the deletion of one of a pair of glutamic acid residues (c.904_906delGAG/c.907_909delGAG; p.Glu302del/Glu303del; ΔE 302/303) near the carboxyl-terminus of torsinA, a member of the AAA+ protein family that localizes to the endoplasmic reticulum (ER) lumen and nuclear envelope (NE). This deletion commonly underlies early-onset DYT1 dystonia. While the role of the disease-causing mutation, torsinAΔE, has been established through genetic association studies, it is much less clear whether other rare human variants of torsinA are pathogenic. Two missense variations have been described in single patients; R288Q (c.863G>A; p.Arg288Gln; R288Q) identified in a patient with onset of severe generalized dystonia and myoclonus since infancy, and F205I (c.613T>A, p.Phe205Ile; F205I) in a psychiatric patient with late-onset focal dystonia. In this study, we have undertaken a series of analyses comparing the biochemical and cellular effects of these rare variants to torsinAΔE and wild-type (wt) torsinA in order to reveal whether there are common dysfunctional features. The results revealed that the variants, R288Q and F205I, are more similar in their properties to torsinAΔE protein than to torsinAwt. These findings provide functional evidence for the potential pathogenic nature of these rare sequence variants in the TOR1A gene, thus implicating these pathologies in the development of dystonia.

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Arresting a Torsin ATPase Reshapes the Endoplasmic Reticulum

Cited by 35 publications

References 39 publications

The mechanism of Torsin ATPase activation

The mechanism of Torsin ATPase activation

Site-specific Proteolysis Mobilizes TorsinA from the Membrane of the Endoplasmic Reticulum (ER) in Response to ER Stress and B Cell Stimulation

Biochemical and Cellular Analysis of Human Variants of the DYT1 Dystonia Protein, TorsinA/TOR1A

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