Order out of Disorder: Working Cycle of an Intrinsically Unfolded Chaperone

Reichmann, Dana; Xu, Ying; Cremers, Claudia M.; Ilbert, Marianne; Mittelman, Roni; Fitzgerald, Michael C.; Jakob, Ursula

doi:10.1016/j.cell.2012.01.045

Cited by 121 publications

(154 citation statements)

References 36 publications

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“…These shifts in conformation and activity are evident in autoinhibited signaling proteins (38) and are supported by the recent capture of SurA in a P1-core open conformation (26). Furthermore, the shifts in both activity and stability revealed here are interestingly similar to the functional transient disorder exhibited by another ATP-independent chaperone, Hsp33 (39). Although the cytoplasmic Hsp33 chaperone is regulated by oxidative stress, it is tempting to consider that SurA P1 too may become transiently unstable in response to activation and that this destabilization may promote substrate recognition and chaperone activity.…”

Section: Discussionsupporting

confidence: 57%

The Activity of Escherichia coli Chaperone SurA Is Regulated by Conformational Changes Involving a Parvulin Domain

et al. 2016

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The periplasmic chaperone SurA is critical for the biogenesis of outer membrane proteins (OMPs) and, thus, the maintenance of membrane integrity in Escherichia coli. The activity of this modular chaperone has been attributed to a core chaperone module, with only minor importance assigned to the two SurA peptidyl-prolyl isomerase (PPIase) domains. In this work, we used synthetic phenotypes and covalent tethering to demonstrate that the activity of SurA is regulated by its PPIase domains and, furthermore, that its activity is correlated with the conformational state of the chaperone. When combined with mutations in the ␤-barrel assembly machine (BAM), SurA mutations resulting in deletion of the second parvulin domain (P2) inhibit OMP assembly, suggesting that P2 is involved in the regulation of SurA. The first parvulin domain (P1) potentiates this autoinhibition, as mutations that covalently tether the P1 domain to the core chaperone module severely impair OMP assembly. Furthermore, these inhibitory mutations negate the suppression of and biochemically stabilize the protein specified by a well-characterized gain-of-function mutation in P1, demonstrating that SurA cycles between distinct conformational and functional states during the OMP assembly process. IMPORTANCEThis work reveals the reversible autoinhibition of the SurA chaperone imposed by a heretofore underappreciated parvulin domain. Many ␤-barrel-associated outer membrane (OM) virulence factors, including the P-pilus and type I fimbriae, rely on SurA for proper assembly; thus, a mechanistic understanding of SurA function and inhibition may facilitate antibiotic intervention against Gram-negative pathogens, such as uropathogenic Escherichia coli, E. coli O157:H7, Shigella, and Salmonella. In addition, SurA is important for the assembly of critical OM biogenesis factors, such as the lipopolysaccharide (LPS) transport machine, suggesting that specific targeting of SurA may provide a useful means to subvert the OM barrier.T he Gram-negative bacterial outer membrane (OM) is an essential, selectively permeable barrier between the cell and its external environment. This asymmetric bilayer affords Gramnegative bacteria resistance to a wide range of antimicrobial compounds and membrane perturbants due to strong lateral interactions between lipopolysaccharides (LPS) in the outer leaflet (1, 2). In order to maintain selective permeability, the OM is replete with integral ␤-barrel outer membrane proteins (OMPs), some of which serve as pores for nutrient diffusion. The transport and assembly of these ␤-barrel proteins comprise a complicated multistep process, from their secretion through the inner membrane translocase (Sec) machinery to transport across the aqueous periplasm and assembly into the OM by the ␤-barrel assembly machine (BAM) complex (3).Prior to their assembly in the OM by BAM, these aggregationprone, insoluble ␤-barrel substrates must be maintained in a folding-competent state as they traverse the aqueous, oxidizing periplasm. This maintenance is ...

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Section: Discussionsupporting

confidence: 57%

The Activity of Escherichia coli Chaperone SurA Is Regulated by Conformational Changes Involving a Parvulin Domain

et al. 2016

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“…This situation is best described as an order-to-disorder transition of the NTDs: They are more confined when engaged in intersubunit interactions in higher-order oligomers and more disordered when exposed to the solvent in smaller species. Order-to-disorder transitions have also been found in the context of client interactions for other chaperones (58)(59)(60). In general, intrinsically disordered regions are known to promote binding promiscuity and may thus be important for the ability of chaperones to bind clients differing in structure and sequence (61)(62)(63).…”

Section: N-terminal Flexibility Facilitates Client Reactivation By Thmentioning

confidence: 92%

Regulated structural transitions unleash the chaperone activity of αB-crystallin

Peschek

Braun

Rohrberg

et al. 2013

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

159

169

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The small heat shock protein αB-crystallin is an oligomeric molecular chaperone that binds aggregation-prone proteins. As a component of the proteostasis system, it is associated with cataract, neurodegenerative diseases, and myopathies. The structural determinants for the regulation of its chaperone function are still largely elusive. Combining different experimental approaches, we show that phosphorylation-induced destabilization of intersubunit interactions mediated by the N-terminal domain (NTD) results in the remodeling of the oligomer ensemble with an increase in smaller, activated species, predominantly 12-mers and 6-mers. Their 3D structures determined by cryo-electron microscopy and biochemical analyses reveal that the NTD in these species gains flexibility and solvent accessibility. These modulated properties are accompanied by an increase in chaperone activity in vivo and in vitro and a more efficient cooperation with the heat shock protein 70 system in client folding. Thus, the modulation of the structural flexibility of the NTD, as described here for phosphorylation, appears to regulate the chaperone activity of αB-crystallin rendering the NTD a conformational sensor for nonnative proteins.olecular chaperones share the ability to bind nonnative, aggregation-prone polypeptides and assist their folding and assembly (1-3). Among these, the small heat shock protein (sHsp) αB-crystallin (also HspB5) is one of the major constituents of the vertebrate eye lens where it functions both as a chaperone and structural protein (4, 5). In nonlenticular tissues, αB-crystallin (αB) participates in sustaining cellular proteostasis. The involvement in neurodegenerative diseases (6, 7), multiple sclerosis (8), myopathies (9), as well as in cell cycle control, apoptosis, and cancer (10, 11) underlines its importance for cellular proteostasis.αB exhibits a tripartite organization (Fig. 1A) with a central α-crystallin domain (ACD) flanked by an N-terminal domain (NTD) and a short C-terminal extension (CTE) (12, 13). The ACD forms stable dimers (14-16) that further assemble into higher-order oligomers via interactions mediated by the NTD and CTE (17)(18)(19). αB forms dynamic populations of multimers with a variable number of subunits (20,21). Structural studies indicate that the variety of oligomeric states including a symmetric 24-mer (22) is created by addition of subunits to (or subtraction from) existing oligomers (17, 18). As for many other sHsps (23), the polydispersity of αB is coupled to spontaneous subunit exchange of yet undetermined units. αB quaternary dynamics was attributed to fluctuations of the intersubunit contacts mediated by the C-terminal IXI motif (24). However, given its involvement in oligomer formation, the NTD must also play a decisive role.In general, sHsps including αB recognize aggregation-prone, partially unfolded substrates (4, 25, 26) and keep them in a refolding-competent state (27, 28). The substrate binding sites of sHsps have not been defined yet. Recent studies suggest the involvement ...

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“…189 This chaperone, which protects organisms against oxidative stress, is inactive in its fully folded state, but it undergoes oxidative unfolding within its redox-sensor domain upon stress. The IDR thus generated is used to discriminate between unfolded and folded partners.…”

Section: 187mentioning

confidence: 99%