Nature structural & molecular biology最新文献

Transthyretin (TTR) is a natively tetrameric thyroxine transporter in blood and cerebrospinal fluid whose misfolding and aggregation causes TTR amyloidosis. A rational drug design campaign identified the small molecule tafamidis (Vyndamax) as a stabilizer of the native TTR fold, and this aggregation inhibitor is regulatory agency approved for the treatment of TTR amyloidosis. Here we used cryo-EM to investigate the conformational landscape of this 55 kDa tetramer in the absence and presence of one or two ligands, revealing inherent asymmetries in the tetrameric architecture and previously unobserved conformational states. These findings provide critical mechanistic insights into negatively cooperative ligand binding and the structural pathways responsible for TTR amyloidogenesis, underscoring the capacity of cryo-EM to identify pharmacological targets suppressed by the confines of the crystal lattice, opening uncharted territory in structure-based drug design.

Random X-chromosome inactivation is a hallmark of female mammalian somatic cells. This epigenetic mechanism, mediated by the long noncoding RNA Xist, occurs in the early embryo and is stably maintained throughout life, although inactivation is lost during primordial germ cell (PGC) development. Using a combination of single-cell allele-specific RNA sequencing and low-input chromatin profiling on developing mouse PGCs, we provide a detailed map of X-linked gene reactivation. Despite the absence of Xist expression, PGCs still harbor a fully silent X chromosome at embryonic day 9.5 (E9.5). Subsequently, X-linked genes undergo gradual and distinct regional reactivation. At E12.5, a substantial part of the inactive X chromosome resists reactivation, retaining an epigenetic memory of its silencing. Our findings define the orchestration of reactivation of the inactive X chromosome, a key event in female PGC reprogramming with direct implications for reproduction.

Botulinum neurotoxins (BoNTs) rank among the most potent toxins and many of them are produced by bacteria carrying the orfX gene cluster that also encodes four nontoxic proteins (OrfX1, OrfX2, OrfX3 and P47). The orfX gene cluster is also found in the genomes of many non-BoNT-producing bacteria, often alongside genes encoding oral insecticidal toxins. However, the functions of these OrfXs and P47 remain elusive. Here, we demonstrate that the combined action of all four components (OrfXs and P47) drastically boosts the oral toxicity of BoNT in mice, following proteolytic activation by digestive proteases that oral toxins regularly confront. In particular, OrfX2 adopts a self-inhibiting state, engaging with BoNT through another clostridial protein, nontoxic non-hemagglutinin (NTNH), only after proteolytic activation. Cryo-electron microscopy studies unveil that two molecules of protease-activated OrfX2 simultaneously associate with NTNH, a binding mode crucial for boosting BoNT oral toxicity. Collectively, these studies offer novel insights into the physiological functions and regulatory mechanisms of OrfXs and P47 of BoNTs, shedding light on the pathogenesis of other bacterial toxins associated with homologous OrfXs and P47.

Fascin cross-links actin filaments (F-actin) into bundles that support tubular membrane protrusions including filopodia and stereocilia. Fascin dysregulation drives aberrant cell migration during metastasis, and fascin inhibitors are under development as cancer therapeutics. Here, we use cryo-EM, cryo-electron tomography coupled with custom denoising and computational modeling to probe human fascin-1’s F-actin cross-linking mechanisms across spatial scales. Our fascin cross-bridge structure reveals an asymmetric F-actin binding conformation that is allosterically blocked by the inhibitor G2. Reconstructions of seven-filament hexagonal bundle elements, variability analysis and simulations show how structural plasticity enables fascin to bridge varied interfilament orientations, accommodating mismatches between F-actin’s helical symmetry and bundle hexagonal packing. Tomography of many-filament bundles and modeling uncover geometric rules underlying emergent fascin binding patterns, as well as the accumulation of unfavorable cross-links that limit bundle size. Collectively, this work shows how fascin harnesses fine-tuned nanoscale structural dynamics to build and regulate micron-scale F-actin bundles.

Intron removal during pre-mRNA splicing is of extraordinary complexity and its disruption causes a vast number of genetic diseases in humans. While key steps of the canonical spliceosome cycle have been revealed by combined structure–function analyses, structural information on an aberrant spliceosome committed to premature disassembly is not available. Here, we report two cryo-electron microscopy structures of post-B^act spliceosome intermediates from Schizosaccharomyces pombe primed for disassembly. We identify the DEAH-box helicase–G-patch protein pair (Gih35–Gpl1, homologous to human DHX35–GPATCH1) and show how it maintains catalytic dormancy. In both structures, Gpl1 recognizes a remodeled active site introduced by an overstabilization of the U5 loop I interaction with the 5′ exon leading to a single-nucleotide insertion at the 5′ splice site. Remodeling is communicated to the spliceosome surface and the Ntr1 complex that mediates disassembly is recruited. Our data pave the way for a targeted analysis of splicing quality control.

Drugs targeting the ghrelin receptor hold therapeutic potential in anorexia, obesity and diabetes. However, developing effective drugs is challenging. To tackle this common issue across a broad drug target, this study aims to understand how anamorelin, the only approved drug targeting the ghrelin receptor, operates compared to other synthetic drugs. Our research elucidated the receptor’s structure with anamorelin and miniG_q, unveiling anamorelin’s superagonistic activity. We demonstrated that ligands with distinct chemical structures uniquely bind to the receptor, resulting in diverse conformations and biasing signal transduction. Moreover, our study showcased the utility of structural information in effectively identifying natural genetic variations altering drug action and causing severe functional deficiencies, offering a basis for selecting the right medication on the basis of the individual’s genomic sequence. Thus, by building on structural analysis, this study enhances the foundational framework for selecting therapeutic agents targeting the ghrelin receptor, by effectively leveraging signaling bias and genetic variations.

Lysosomal membrane protein LYCHOS (lysosomal cholesterol signaling) translates cholesterol abundance to mammalian target of rapamycin activation. Here we report the 2.11-Å structure of human LYCHOS, revealing a unique fusion architecture comprising a G-protein-coupled receptor (GPCR)-like domain and a transporter domain that mediates homodimer assembly. The NhaA-fold transporter harbors a previously uncharacterized intramembrane Na⁺ pocket. The GPCR-like domain is stabilized, by analogy to canonical GPCRs, in an inactive state through ‘tethered antagonism’ by a lumenal loop and strong interactions at the cytosol side preventing the hallmark swing of the sixth transmembrane helix seen in active GPCRs. A cholesterol molecule and an associated docosahexaenoic acid (DHA)-phospholipid are entrapped between the transporter and GPCR-like domains, with the DHA-phospholipid occupying a pocket previously implicated in cholesterol sensing, indicating inter-domain coupling via dynamic lipid–protein interactions. Our work provides a high-resolution framework for functional investigations of the understudied LYCHOS protein.

Thymidine kinase 1 (TK1), a crucial enzyme in DNA synthesis, is highly expressed in various cancers. However, the mechanisms underlying its elevated expression and the implications for tumor metabolism remain unclear. Here we demonstrate that activation of growth factor receptors enhances TK1 expression. Treatment with epidermal growth factor or insulin-like growth factor 1 induces the binding of ERK1/2 to TK1 and subsequent TK1 S13/231 phosphorylation by ERK1/2. This modification recruits ubiquitin carboxyl-terminal hydrolase 9X to deubiquitylate TK1, preventing its proteasomal degradation. Stabilized TK1 not only enhances its enzyme activity-dependent deoxythymidine monophosphate production for DNA synthesis but also promotes glycolysis independently of its enzymatic activity by upregulating phosphofructokinase/fructose bisphosphatase type 3 expression. This dual role of TK1 drives the proliferation of human hepatocellular carcinoma cells and liver tumor growth in mice. Our findings reveal a crucial mechanism by which growth factors promote tumor development through TK1-mediated DNA synthesis and glycolysis and highlight TK1 as a potential molecular target for cancer treatment.

Cholesterol plays a pivotal role in modulating the activity of mechanistic target of rapamycin complex 1 (mTOR1), thereby regulating cell growth and metabolic homeostasis. LYCHOS, a lysosome-localized G-protein-coupled receptor-like protein, emerges as a cholesterol sensor and is capable of transducing the cholesterol signal to affect the mTORC1 function. However, the precise mechanism by which LYCHOS recognizes cholesterol remains unknown. Here, using cryo-electron microscopy, we determined the three-dimensional structural architecture of LYCHOS in complex with cholesterol molecules, revealing a unique arrangement of two sequential structural domains. Through a comprehensive analysis of this structure, we elucidated the specific structural features of these two domains and their collaborative role in the process of cholesterol recognition by LYCHOS.

Human immunodeficiency virus-1 (HIV-1) uses a number of strategies to modulate viral and host gene expression during its life cycle. To characterize the transcriptional and translational landscape of HIV-1 infected cells, we used a combination of ribosome profiling, disome sequencing and RNA sequencing. We show that HIV-1 messenger RNAs are efficiently translated at all stages of infection, despite evidence for a substantial decrease in the translational efficiency of host genes that are implicated in host cell translation. Our data identify upstream open reading frames in the HIV-1 5′-untranslated region as well as internal open reading frames in the Vif and Pol coding domains. We also observed ribosomal collisions in Gag-Pol upstream of the ribosome frameshift site that we attributed to an RNA structural fold using RNA structural probing and functional analysis. Antisense oligonucleotides designed to alter the base of this structure decreased frameshift efficiency. Overall, our data highlight the complexity of HIV-1 gene regulation and provide a key resource for decoding of host–pathogen interactions upon HIV-1 infection. Furthermore, we provide evidence for a RNA structural fold including the frameshift site that could serve as a target for antiviral therapy.