In vivo aspects of protein folding and quality control Balchin, David; Hayer-Hartl, Manajit; Hartl, F. Ulrich
Science (American Association for the Advancement of Science),
07/2016, Volume:
353, Issue:
6294
Journal Article
Peer reviewed
Open access
Most proteins must fold into unique three-dimensional structures to perform their biological functions. In the crowded cellular environment, newly synthesized proteins are at risk of misfolding and ...forming toxic aggregate species. To ensure efficient folding, different classes of molecular chaperones receive the nascent protein chain emerging from the ribosome and guide it along a productive folding pathway. Because proteins are structurally dynamic, constant surveillance of the proteome by an integrated network of chaperones and protein degradation machineries is required to maintain protein homeostasis (proteostasis). The capacity of this proteostasis network declines during aging, facilitating neurodegeneration and other chronic diseases associated with protein aggregation. Understanding the proteostasis network holds the promise of identifying targets for pharmacological intervention in these pathologies.
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BFBNIB, NMLJ, NUK, ODKLJ, PNG, SAZU, UL, UM, UPUK
Protein Misfolding Diseases Hartl, F. Ulrich
Annual review of biochemistry,
06/2017, Volume:
86, Issue:
1
Journal Article
Peer reviewed
The majority of protein molecules must fold into defined three-dimensional structures to acquire functional activity. However, protein chains can adopt a multitude of conformational states, and their ...biologically active conformation is often only marginally stable. Metastable proteins tend to populate misfolded species that are prone to forming toxic aggregates, including soluble oligomers and fibrillar amyloid deposits, which are linked with neurodegeneration in Alzheimer and Parkinson disease, and many other pathologies. To prevent or regulate protein aggregation, all cells contain an extensive protein homeostasis (or proteostasis) network comprising molecular chaperones and other factors. These defense systems tend to decline during aging, facilitating the manifestation of aggregate deposition diseases. This volume of the
Annual Review of Biochemistry
contains a set of three articles addressing our current understanding of the structures of pathological protein aggregates and their associated disease mechanisms. These articles also discuss recent insights into the strategies cells have evolved to neutralize toxic aggregates by sequestering them in specific cellular locations.
The biological functions of proteins are governed by their three-dimensional fold. Protein folding, maintenance of proteome integrity, and protein homeostasis (proteostasis) critically depend on a ...complex network of molecular chaperones. Disruption of proteostasis is implicated in aging and the pathogenesis of numerous degenerative diseases. In the cytosol, different classes of molecular chaperones cooperate in evolutionarily conserved folding pathways. Nascent polypeptides interact cotranslationally with a first set of chaperones, including trigger factor and the Hsp70 system, which prevent premature (mis)folding. Folding occurs upon controlled release of newly synthesized proteins from these factors or after transfer to downstream chaperones such as the chaperonins. Chaperonins are large, cylindrical complexes that provide a central compartment for a single protein chain to fold unimpaired by aggregation. This review focuses on recent advances in understanding the mechanisms of chaperone action in promoting and regulating protein folding and on the pathological consequences of protein misfolding and aggregation.
Ageing is a major risk factor for the development of many diseases, prominently including neurodegenerative disorders such as Alzheimer disease and Parkinson disease. A hallmark of many age-related ...diseases is the dysfunction in protein homeostasis (proteostasis), leading to the accumulation of protein aggregates. In healthy cells, a complex proteostasis network, comprising molecular chaperones and proteolytic machineries and their regulators, operates to ensure the maintenance of proteostasis. These factors coordinate protein synthesis with polypeptide folding, the conservation of protein conformation and protein degradation. However, sustaining proteome balance is a challenging task in the face of various external and endogenous stresses that accumulate during ageing. These stresses lead to the decline of proteostasis network capacity and proteome integrity. The resulting accumulation of misfolded and aggregated proteins affects, in particular, postmitotic cell types such as neurons, manifesting in disease. Recent analyses of proteome-wide changes that occur during ageing inform strategies to improve proteostasis. The possibilities of pharmacological augmentation of the capacity of proteostasis networks hold great promise for delaying the onset of age-related pathologies associated with proteome deterioration and for extending healthspan.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The bacterial chaperonin GroEL and its cofactor GroES constitute the paradigmatic molecular machine of protein folding. GroEL is a large double-ring cylinder with ATPase activity that binds ...non-native substrate protein (SP) via hydrophobic residues exposed towards the ring center. Binding of the lid-shaped GroES to GroEL displaces the bound protein into an enlarged chamber, allowing folding to occur unimpaired by aggregation. GroES and SP undergo cycles of binding and release, regulated allosterically by the GroEL ATPase. Recent structural and functional studies are providing insights into how the physical environment of the chaperonin cage actively promotes protein folding, in addition to preventing aggregation. Here, we review different models of chaperonin action and discuss issues of current debate.
The group I chaperonin GroEL and its cofactor GroES are essential components of the cellular machinery of protein folding in bacteria. Homologous chaperonins occur in mitochondria and chloroplast, while more distantly related group II chaperonins are found in archaea and the eukaryotic cytosol.
GroEL is a double-ring complex with ATPase activity that binds non-native SP in the ring opening. Binding of the lid-shaped GroES to GroEL results in the displacement of SP into an enclosed nano-cage for folding to occur unimpaired by aggregation.
GroEL, non-native protein, and GroES undergo ATP-regulated binding and release cycles.
Recent advances indicate that the physical environment of the GroEL–GroES cage can accelerate the folding of some SPs. An effect of steric confinement of SP in the cage may contribute to the rate enhancement of folding.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The ATP-dependent Hsp70 chaperones (DnaK in E. coli) mediate protein folding in cooperation with J proteins and nucleotide exchange factors (E. coli DnaJ and GrpE, respectively). The Hsp70 system ...prevents protein aggregation and increases folding yields. Whether it also enhances the rate of folding remains unclear. Here we show that DnaK/DnaJ/GrpE accelerate the folding of the multi-domain protein firefly luciferase (FLuc) ~20-fold over the rate of spontaneous folding measured in the absence of aggregation. Analysis by single-pair FRET and hydrogen/deuterium exchange identified inter-domain misfolding as the cause of slow folding. DnaK binding expands the misfolded region and thereby resolves the kinetically-trapped intermediates, with folding occurring upon GrpE-mediated release. In each round of release DnaK commits a fraction of FLuc to fast folding, circumventing misfolding. We suggest that by resolving misfolding and accelerating productive folding, the bacterial Hsp70 system can maintain proteins in their native states under otherwise denaturing stress conditions.
Molecular chaperones are highly conserved proteins that promote proper folding of other proteins in vivo. Diverse chaperone systems assist de novo protein folding and trafficking, the assembly of ...oligomeric complexes, and recovery from stress‐induced unfolding. A fundamental function of molecular chaperones is to inhibit unproductive protein interactions by recognizing and protecting hydrophobic surfaces that are exposed during folding or following proteotoxic stress. Beyond this basic principle, it is now clear that chaperones can also actively and specifically accelerate folding reactions in an ATP‐dependent manner. We focus on the bacterial Hsp70 and chaperonin systems as paradigms, and review recent work that has advanced our understanding of how these chaperones act as catalysts of protein folding.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Most proteins must fold into precise three-dimensional conformations to fulfill their biological functions. Here we review recent concepts emerging from studies of protein folding in vitro and in ...vivo, with a focus on how proteins navigate the complex folding energy landscape inside cells with the aid of molecular chaperones. Understanding these reactions is also of considerable medical relevance, as the aggregation of misfolding proteins that escape the cellular quality-control machinery underlies a range of debilitating diseases, including many age-onset neurodegenerative disorders.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A major challenge faced by human civilization is to ensure that agricultural productivity keeps pace with population growth and a changing climate. All food supply is generated, directly or ...indirectly, through the process of photosynthesis, with the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyzing the assimilation of atmospheric CO2. Despite its pivotal role, Rubisco is a remarkably inefficient enzyme and must be made by plants in large quantities. However, efforts to enhance Rubisco performance by bioengineering have been hampered by its extensive reliance on molecular chaperones and auxiliary factors for biogenesis, metabolic repair, and packaging into membraneless microcompartments. Here, we review recent advances in understanding these complex machineries and discuss their implications for improving Rubisco carboxylase activity with the goal to increase crop yields.
Rubisco is the key enzyme of carbon fixation in photosynthesis. Essentially all biomass and thus food source is directly or indirectly produced by Rubisco.Rubisco is an inefficient enzyme: it has a low turnover rate, can fix O2 instead of CO2 and is prone to self-inhibition.Recent advances revealed the extensive requirement of Rubisco for chaperones and other auxiliary factors for folding, assembly and functional maintenance.Introducing these chloroplast auxiliary factors into bacteria now allows the recombinant expression of plant Rubisco for large scale mutational screening.Nonmembranous compartments in cyanobacteria and algae serve to concentrate CO2 for enhanced Rubisco function. Generation of these compartments requires the formation of liquid-like Rubisco condensates by specific linker proteins.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Huntington’s disease is one of several neurodegenerative disorders characterized by the aggregation of polyglutamine (polyQ)-expanded mutant protein. How polyQ aggregation leads to cellular ...dysfunction is not well understood. Here, we analyzed aberrant protein interactions of soluble oligomers and insoluble inclusions of mutant huntingtin using in-cell single molecule fluorescence spectroscopy and quantitative proteomics. We find that the interactome of soluble oligomers is highly complex, with an enrichment of RNA-binding proteins as well as proteins functioning in ribosome biogenesis, translation, transcription, and vesicle transport. The oligomers frequently target proteins containing extended low-complexity sequences, potentially interfering with key cellular pathways. In contrast, the insoluble inclusions are less interactive and associate strongly with protein quality control components, such as Hsp40 chaperones and factors of the ubiquitin-proteasome system. Our results suggest a “multiple hit” model for the pathogenic effects of mutant huntingtin, with soluble forms engaging more extensively in detrimental interactions than insoluble aggregates.
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•Soluble oligomers and inclusions of polyQ-expanded huntingtin coexist in N2a cells•Oligomers engage in aberrant interactions with multiple key cellular proteins•Oligomers target RNA-binding proteins containing low-complexity sequences•Inclusions are less interactive, consistent with their formation being protective
Huntington’s disease is a neurodegenerative disorder caused by the aggregation of polyglutamine-expanded huntingtin. Kim et al. show that soluble huntingtin oligomers engage in aberrant interactions with numerous key cellular proteins containing low-complexity sequences. Huntingtin inclusions are less interactive. Our results suggest a “multiple hit” model for the pathogenic effects of mutant huntingtin.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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