Protein folding

Biochemical and structural analysis of intermediates during multipass membrane protein biogenesis showed how an intramembrane chaperone guides nascent membrane proteins to a semi-enclosed lipid-filled cavity where they are inserted and folded correctly.

Biochemical reconstitution and functional analysis reveal how newly synthesized multipass membrane proteins dynamically remodel the translocon to facilitate their successful biogenesis.

Ageing alters the kinetics of translation elongation in both Caenorhabditis elegans and Saccharomyces cerevisiae.

The cryo-electron microscopy structure of the glucocorticoid receptor (GR)-loading complex—a complex in which Hsp70 loads GR onto Hsp90 and Hop—is described, providing insights into how the chaperones Hsp90 and Hsp70 coordinate to facilitate GR remodelling for activation.

Studies based on cryo-electron microscopy structures of Hsp90 chaperone complexes reveal the molecular mechanism of the chaperone-mediated maturation of the human glucocorticoid receptor.

The trRosetta neural network was used to iteratively optimise model proteins from random 100-amino-acid sequences, resulting in ‘hallucinated’ proteins, which when expressed in bacteria closely resembled the model structures.

A protein chaperone system is identified that consists of proteins with poly-Asp/Glu sequence, and may have an important role in diseases characterized by protein aggregation.

The binding and activation of HSP70 by class B J-domain proteins is subject to an autoinhibitory regulatory mechanism that controls substrate targeting to HSP70 and is required for the disaggregation of amyloid fibres.

The molecular steps that lead to the disaggregation of amyloid fibrils are shown to involve the synergistic action of HSP70 and its co-chaperones DNAJB1 and HSP110.

An approach for the design of protein pores is demonstrated by the computational design and subsequent experimental expression of both an ion-selective and a large transmembrane pore.

The PAT complex, an intermembrane chaperone complex comprising the ER-resident membrane proteins CCDC47 and Asterix, directly interacts with nascent transmembrane domains to facilitate the biogenesis of multi-spanning membrane proteins.

A systematic analysis of the proteostasis network of secreted proteins in Caenorhabditis elegans identifies numerous regulators of protein homeostasis outside the cell, and highlights the contribution of extracellular proteostasis to host defence.

Cryo-electron microscopy structures of a folding intermediate on the BAM complex of Escherichia coli reveal how interactions between the BamA catalyst and substrate permit stable association during folding, followed by rapid turnover.

A combination of optical tweezers and fluorescent-particle tracking is used to dissect the dynamics of the Hsp100 disaggregase ClpB, and show that the processive extrusion of polypeptide loops is the mechanistic basis of its activity.

Chaperones interact with a canonical motif in α-synuclein, which can be prevented by phosphorylation of α-synuclein at Tyr39, whereas inhibition of this interaction leads to the localization of α-synuclein to the mitochondria and aggregate formation.

iNOS-driven dysregulation of the IRE1α–XBP1 pathway leads to cardiomyocyte dysfunction in mice and recapitulates the systemic and cardiovascular features of human heart failure with preserved ejection fraction.

Ubiquitin chains linked to cytoplasmic misfolded proteins are different from those linked to nuclear misfolded proteins, each requiring a distinct combination of molecular chaperones and ubiquitination circuitries.

The structures of tau filaments from patients with the neurodegenerative disorder Pick’s disease show that the filament fold is different from that of the tau filaments found in Alzheimer’s disease.

Cotranslational assembly is a prevalent mechanism for the formation of oligomeric complexes in Saccharomyces cerevisiae, with one subunit serving as scaffold for the translation of partner subunits.

Sperm-activated lysosomes enhance proteostasis in nematode oocytes just before fertilization; this could prevent transmission of damaged proteins to the next generation and may explain the immortality of the germ-cell lineage.

Proteins prone to aggregation in yeast are imported into mitochondria under stress conditions, suggesting that mitochondrial import and proteolysis may help to disaggregate proteins in the cytoplasm.

Hsp70 binds unfolded protein segments in its groove, but can also bind and stabilize folded protein structures, owing to its moveable lid, with ATP hydrolysis and co-chaperones allowing control of these contrasting effects.

Chaperomes are dynamic assemblies of proteins that regulate cellular homeostasis but specific cellular stresses remodel chaperome components into a stable chaperome network called the epichaperome, which might offer a new cancer target.

The solution structure of SecB, a molecular chaperone that exhibits strong antifolding activity, in complex with alkaline phosphatase and maltose-binding protein captured in their unfolded states.

The signal recognition particle (SRP) preferentially binds peptides destined for secretion before peptide-targeting signals are translated through recognition of elements in their mRNA, including non-coding sequences.

Acute protein folding stress in the mitochondrial matrix activates both increased chaperone availability within the matrix and reduced matrix-localized protein synthesis through translational inhibition.

Defects in the ribosome quality control (RQC) complex, which clears proteins that stalled during translation, can cause neurodegeneration; here it is shown that in RQC-defective cells a peptide tail added by the RQC subunit 2 to stalled polypeptides promotes their aggregation and the sequestration of chaperones in these aggregates, affecting normal protein quality control processes.

A new deep proteomic analysis method is used to identify proteins that interact with wild-type cystic fibrosis transmembrane conductance regulator (CFTR) and its mutant version that is the major cause of cystic fibrosis.

An efficient protein disaggregation system uncovered in metazoan cells requires transient interactions between J-protein co-chaperones of classes A and B, which synergistically boost HSP70-dependent disaggregation activity, providing a flexible further level of regulation for metazoan protein quality control, with direct relevance to human diseases such as age-related neurodegeneration.

The structural polymorphism of intrinsically disordered protein 4E-BP2 allows it to regulate translation initiation through post-translational modification-mediated folding, exemplifying a new and potentially general mechanism of biological regulation mediated by intrinsically disordered proteins.

Lipopolysaccharide, an essential component of the outer membranes of Gram-negative bacteria, is inserted by LptD–LptE, a protein complex with a unique ‘barrel and plug’ architecture; the structure, molecular dynamics simulations and functional assays of the LptD–LptE complex of Salmonella typhimurium suggest that lipopolysaccharide may pass through the barrel and is then inserted into the outer leaflet of the outer membrane through a lateral opening between two β-strands of LptD.

Molecular, pharmacological and functional data show that haematopoietic stem cells (HSCs) are predisposed to ER-stress-mediated apoptosis compared to closely related progenitors; a framework for understanding how stress signalling is coordinated within the hematopoietic hierarchy and integrated with stemness is provided, and may have implications for the improvement of clinical transplantation of HSCs.

Here the Kramers diffusion coefficient and free-energy barrier are characterized for the first time through single-molecule fluorescence measurements of the temperature- and viscosity-dependence of the transition path time for protein folding.

The crystal structure of BamA, the central component of the β-barrel assembly machinery (BAM) complex, from N. gonorrhoeae and H. ducreyi is determined; the structure consists of an interior cavity capped by extracellular loops, an exterior rim with a narrowed hydrophobic surface and a lateral opening of the barrel domain, providing insight into a possible route for the insertion of β-barrel membrane proteins into the bacterial outer membrane.

Biochemical and structural investigation of a model for prion-induced neurodegeneration—antibody binding to PrP^C—reveals the role of the PrP flexible tail and reactive oxygen species in mediating toxicity.

The bacterial chaperone named trigger factor is found to stabilize protein folding intermediates that eventually convert to the native state, suggesting that chaperones play a direct role in instructing protein folding.

MERS-CoV is a newly emerged coronavirus that is related to SARS-CoV and has proven fatal in half of the people it has infected to date: here the crystal structure of the MERS-CoV receptor binding domain is presented in complex with its receptor on human cells, CD26.

It is shown that the formation of amyloid-β oligomers, one of the histopathological signatures of Alzheimer’s disease, can be triggered by small quantities of a specifically truncated and post-translationally modified version of amyloid-β.

Shifts in the position of adherens junctions, triggered by a change in the ratio of Bazooka and Par-1, initiate epithelial folding in the Drosophila embryo.

Aneuploidy is shown to be induced by pleiotropic stress conditions (especially Hsp90 inhbition) in yeast, leading to stress adaptation.

Human neurons derived from induced pluripotent stem cells permit the study of aberrant protein processing and aggregation in Machado–Joseph disease.

Proteins often comprise domains that can be distinguished as relatively separate regions in the three-dimensional structure. Communication between these domains is important for catalysis, regulation and folding, but how they communicate is largely unclear. Here, single-molecule optical tweezers were used to pull on a protein while monitoring the energetics of unfolding and refolding events in disparate regions. By comparing topological variations of the same protein, new rules of cooperation between domains were derived.

The primary sequence of a protein defines its free-energy landscape and thus determines the rate constants of folding and unfolding, with theory suggesting that roughness in the energy landscape leads to slower folding. However, obtaining experimental descriptions of this landscape is challenging. Landscape roughness is now shown to be responsible for the slower folding and unfolding times observed in the R16 and R17 domains of α-spectrin relative to the similar R15 domain.

Group II chaperonins are present in eukaryotes and archaea and are essential mediators of cellular protein folding. This process is critically dependent on the closure of a built-in lid, which is triggered by ATP hydrolysis, but the structural rearrangements and molecular events leading to lid closure are unknown. Using cryo-electron microscopy, the structures of an archaeal group II chaperonin in the open and closed states are now reported, providing details of this mechanism.