16 results found
Larburu N, Adams C, Chen C, et al., 2020, Mechanism of Hsp70 specialised interactions in protein translocation and the unfolded protein response, Open Biology, Vol: 10, Pages: 1-9, ISSN: 2046-2441
Hsp70 chaperones interact with substrate proteins in a coordinated fashion that is regulated by nucleotides and enhanced by assisting cochaperones. There are numerous homologues and isoforms of Hsp70 that participate in a wide variety of cellular functions. This diversity can facilitate adaption or specialisation based on particular biological activity and location within the cell. In this review, we highlight two specialised binding partner proteins, Tim44 and IRE1, that interact with Hsp70 at the membrane in order to serve their respective roles in protein translocation and UPR signaling. Recent mechanistic data suggest analogy in the way the two Hsp70 homologues (BiP and mtHsp70) can bind and release from IRE1 and Tim44 upon substrate engagement. These shared mechanistic features may underlie how Hsp70 interacts with specialised binding partners and may extend our understanding of the mechanistic repertoire that Hsp70 chaperones possess.
Kopp MC, Larburu N, vinoth D, et al., 2019, UPR proteins IRE1 and PERK switch BiP from chaperone to ER stress sensor, Nature Structural and Molecular Biology, Vol: 26, Pages: 1053-1062, ISSN: 1545-9985
BiP is a major ER chaperone and suggested to act as primary sensor in the activationof the unfolded protein response (UPR). How BiP operates as a molecular chaperoneand as an ER stress sensor is unknown. Here, by reconstituting components ofhuman UPR, ER stress and BiP chaperone systems, we discover that the interactionof BiP with the luminal domains (LD) of UPR proteins, IRE1 and PERK, switch BiPfrom its chaperone cycle into an ER stress sensor cycle by preventing the binding ofits cochaperones, with loss of ATPase stimulation. Furthermore, misfolded proteindependentdissociation of BiP from IRE1 is primed by ATP but not ADP. Our dataelucidate a previously unidentified mechanistic cycle of BiP function that explains itsability to act as a Hsp70 chaperone and ER stress sensor.
Adams CJ, Kopp MC, Larburu N, et al., 2019, Structure and molecular mechanism of ER stress signaling by the unfolded protein response signal activator IRE1, Frontiers in Molecular Biosciences, Vol: 6, ISSN: 2296-889X
The endoplasmic reticulum (ER) is an important site for protein folding and maturation in eukaryotes. The cellular requirement to synthesize proteins within the ER is matched by its folding capacity. However, the physiological demands or aberrations in folding may result in an imbalance which can lead to the accumulation of misfolded protein, also known as “ER stress.” The unfolded protein response (UPR) is a cell-signaling system that readjusts ER folding capacity to restore protein homeostasis. The key UPR signal activator, IRE1, responds to stress by propagating the UPR signal from the ER to the cytosol. Here, we discuss the structural and molecular basis of IRE1 stress signaling, with particular focus on novel mechanistic advances. We draw a comparison between the recently proposed allosteric model for UPR induction and the role of Hsp70 during polypeptide import to the mitochondrial matrix.
Sepulveda D, Rojas-Rivera D, Rodriguez DA, et al., 2018, Interactome Screening Identifies the ER Luminal Chaperone Hsp47 as a Regulator of the Unfolded Protein Response Transducer IRE1 alpha, MOLECULAR CELL, Vol: 69, Pages: 238-+, ISSN: 1097-2765
Kopp MC, Nowak PR, Larburu N, et al., 2018, In vitro FRET analysis of IRE1 and BiP association and dissociation upon endoplasmic reticulum stress., Elife, Vol: 7
The unfolded protein response (UPR) is a key signaling system that regulates protein homeostasis within the endoplasmic reticulum (ER). The primary step in UPR activation is the detection of misfolded proteins, the mechanism of which is unclear. We have previously suggested an allosteric mechanism for UPR induction (Carrara et al., 2015) based on qualitative pull-down assays. Here, we develop an in vitro Förster resonance energy transfer (FRET) UPR induction assay that quantifies IRE1 luminal domain and BiP association and dissociation upon addition of misfolded proteins. Using this technique, we reassess our previous observations and extend mechanistic insight to cover other general ER misfolded protein substrates and their folded native state. Moreover, we evaluate the key BiP substrate-binding domain mutant V461F. The new experimental approach significantly enhances the evidence suggesting an allosteric model for UPR induction upon ER stress.
Cerezo M, Lehraiki A, Millet A, et al., 2016, Compounds Triggering ER Stress Exert Anti-Melanoma Effects and Overcome BRAF Inhibitor Resistance, Cancer Cell, Vol: 29, Pages: 805-819, ISSN: 1878-3686
Carrara M, Prischi F, Nowak P, et al., 2015, Crystal structures reveal transient PERK luminal domain tetramerization in endoplasmic reticulum stress signaling, EMBO Journal, Vol: 34, Pages: 1589-1600, ISSN: 0261-4189
Stress caused by accumulation of misfolded proteins within the endoplasmic reticulum (ER) elicits a cellular unfolded protein response (UPR) aimed at maintaining protein‐folding capacity. PERK, a key upstream component, recognizes ER stress via its luminal sensor/transducer domain, but the molecular events that lead to UPR activation remain unclear. Here, we describe the crystal structures of mammalian PERK luminal domains captured in dimeric state as well as in a novel tetrameric state. Small angle X‐ray scattering analysis (SAXS) supports the existence of both crystal structures also in solution. The salient feature of the tetramer interface, a helix swapped between dimers, implies transient association. Moreover, interface mutations that disrupt tetramer formation in vitro reduce phosphorylation of PERK and its target eIF2α in cells. These results suggest that transient conversion from dimeric to tetrameric state may be a key regulatory step in UPR activation.
Carrara M, Prischi F, Nowak PR, et al., 2015, Noncanonical binding of BiP ATPase domain to Ire1 and Perk is dissociated by unfolded protein C(H)1 to initiate ER stress signaling, eLife, Vol: 4, Pages: 1-16, ISSN: 2050-084X
The unfolded protein response (UPR) is an essential cell signaling system that detects the accumulation of misfolded proteins within the endoplasmic reticulum (ER) and initiates a cellular response in order to maintain homeostasis. How cells detect the accumulation of misfolded proteins remains unclear. In this study, we identify a noncanonical interaction between the ATPase domain of the ER chaperone BiP and the luminal domains of the UPR sensors Ire1 and Perk that dissociates when authentic ER unfolded protein CH1 binds to the canonical substrate binding domain of BiP. Unlike the interaction between chaperone and substrates, we found that the interaction between BiP and UPR sensors was unaffected by nucleotides. Thus, we discover that BiP is dual functional UPR sensor, sensing unfolded proteins by canonical binding to substrates and transducing this event to noncanonical, signaling interaction to Ire1 and Perk. Our observations implicate BiP as the key component for detecting ER stress and suggest an allosteric mechanism for UPR induction.
Prischi F, Nowak PR, Carrara M, et al., 2014, Phosphoregulation of Ire1 RNase splicing activity., Nat Commun, Vol: 5
Ire1 is activated in response to accumulation of misfolded proteins within the endoplasmic reticulum as part of the unfolded protein response (UPR). It is a unique enzyme, possessing both kinase and RNase activity that is required for specific splicing of Xbp1 mRNA leading to UPR activation. How phosphorylation impacts on the Ire1 splicing activity is unclear. In this study, we isolate distinct phosphorylated species of Ire1 and assess their effects on RNase splicing both in vitro and in vivo. We find that phosphorylation within the kinase activation loop significantly increases RNase splicing in vitro. Correspondingly, mutants of Ire1 that cannot be phosphorylated on the activation loop show decreased specific Xbp1 and promiscuous RNase splicing activity relative to wild-type Ire1 in cells. These data couple the kinase phosphorylation reaction to the activation state of the RNase, suggesting that phosphorylation of the activation loop is an important step in Ire1-mediated UPR activation.
Carrara M, Prischi F, Ali MMU, 2013, UPR Signal Activation by Luminal Sensor Domains, Int. j. Mol. Sci., Vol: 14
Maruf MUATBELDPRNMCS-SAHCMMGRGJMWAICFEDALHP, 2011, Structure of the Ire1 autophosphorylation complex and implications for the unfolded protein response, EMBO J, Vol: 30, Pages: 894-905
Millson SH, Vaughan CK, Zhai C, et al., 2008, Chaperone ligand-discrimination by the TPR-domain protein Tah1, Biochem J, Pages: 261-268
Buchanan SK, Lukacik P, Grizot S, et al., 2007, Structure of colicin I receptor bound to the R-domain of colicin Ia: implications for protein import, EMBO Journal, Pages: 2594-2604
Ali MMU, Roe SM, Vaughan CK, et al., 2006, Crystal structure of an Hsp90-nucleotide-p23/Sba1 closed chaperone complex, NATURE, Vol: 440, Pages: 1013-1017, ISSN: 0028-0836
Roe SM, Ali MMU, Meyer P, et al., 2004, The mechanism of Hsp90 regulation by the protein kinase-specific cochaperone p50(cdc37), CELL, Vol: 116, Pages: 87-98, ISSN: 0092-8674
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