Ribosome biogenesis is a highly complex process in eukaryotes, involving temporally and spatially regulated ribosomal protein (r-protein) binding and ribosomal RNA remodelling events in the nucleolus, nucleoplasm and cytoplasm1,2. Hundreds of assembly factors, organized into sequential functional groups3,4, facilitate and guide the maturation process into productive assembly branches in and across different cellular compartments. However, the precise mechanisms by which these assembly factors function are largely unknown. Here we use cryo-electron microscopy to characterize the structures of yeast nucleoplasmic pre-60S particles affinity-purified using the epitope-tagged assembly factor Nog2. Our data pinpoint the locations and determine the structures of over 20 assembly factors, which are enriched in two areas: an arc region extending from the central protuberance to the polypeptide tunnel exit, and the domain including the internal transcribed spacer 2 (ITS2) that separates 5.8S and 25S ribosomal RNAs. In particular, two regulatory GTPases, Nog2 and Nog1, act as hub proteins to interact with multiple, distant assembly factors and functional ribosomal RNA elements, manifesting their critical roles in structural remodelling checkpoints and nuclear export. Moreover, our snapshots of compositionally and structurally different pre-60S intermediates provide essential mechanistic details for three major remodelling events before nuclear export: rotation of the 5S ribonucleoprotein, construction of the active centre and ITS2 removal. The rich structural information in our structures provides a framework to dissect molecular roles of diverse assembly factors in eukaryotic ribosome assembly.

Functional nanostructures with high biocompatibility and stability, low toxicity, and specificity of targeting to desired organs or cells are of great interest in nanobiology and medicine. However, the challenge is to integrate all of these desired features into a single nanobiostructure, which can be applied to biomedical applications and eventually in clinical settings. In this context, we designed a strategy to assemble two gold nanoclusters at the ferroxidase active sites of ferritin heavy chain. Our studies showed that the resulting nanostructures (Au-Ft) retain not only the intrinsic fluorescence properties of noble metal, but gain enhanced intensity, show a red-shift, and exhibit tunable emissions due to the coupling interaction between the paired Au clusters. Furthermore, Au-Ft possessed the well-defined nanostructure of native ferritin, showed organ-specific targeting ability, high biocompatibility, and low cytotoxicity. The current study demonstrates that an integrated multimodal assembly strategy is able to generate stable and effective biomolecule-noble metal complexes of controllable size and with desirable fluorescence emission characteristics. Such agents are ideal for targeted in vitro and in vivo imaging. These results thus open new opportunities for biomolecule-guided nanostructure assembly with great potential for biomedical applications.

Metal-organic cages (MOCs) are discrete molecular assemblies formed by coordination bonds between metal nodes and organic ligands. The application of MOCs has been greatly limited due to their poor stability, especially in aqueous solutions. In this work, we thoroughly investigate the stability of several Zr-MOCs and reveal their excellent stability in aqueous solutions with acidic, neutral, and weak basic conditions. In addition, we present for the first time a process-tracing study on the postassembly modification of one MOC, ZrT-1-NH, highlighting the excellent stability and versatility of Zr-MOCs as a new type of molecular platform for various applications.

The single-site catalyst (SSC) characteristic of atomically dispersed active centers will not only maximize the catalytic activity,but also provideapromising platform for establishing the structure-activity relationship.H owever,a rbitrary arrangements of active sites in the existed SSCs make it difficult for mechanism understanding and performance optimization. Now, aw ell-defined ultrathin SSC is fabricated by assembly of metal-porphyrin molecules,w hiche nables the precise identification of the active sites for d-orbital energy engineering.The activity of as-assembled products for electrocatalytic CO 2 reduction is significantly promoted via lifting up the energy level of metal d z 2 orbitals,e xhibiting ar emarkable Faradaic efficiency of 96 %a tt he overpotential of 500 mV. Furthermore,aturnover frequency of 4.21 s À1 is achieved with negligible decayo ver4 8h.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.Figure 5. DFT calculation of electrocatalytic CO 2 reduction on STPyP-Co.A)Calculated free-energys tates of CO 2 reduction to CO on STPyP-Co and MTPyP-Co. B) Optimized geometry of intermediate [STPyP-Co-COOH].C ),D) Spatial representationo fHOMO orbital of [STPyP-Co-COOH] and [MTPyP-Co-COOH] intermediates, respectively.

Despite the rapid development of molecular rotors over the past decade, it still remains a huge challenge to understand their confined behavior in ultrathin two-dimensional (2D) nanomaterials for molecular recognition. Here, we report an all-carbon, 2D π-conjugated aromatic polymer, named NUS-25, containing flexible tetraphenylethylene (TPE) units as aggregation-induced emission (AIE) molecular rotors. NUS-25 bulk powder can be easily exfoliated into micrometer-sized lamellar freestanding nanosheets with a thickness of 2-5 nm. The dynamic behavior of the TPE rotors is partially restricted through noncovalent interactions in the ultrathin 2D nanosheets, which is proved by comparative experimental studies including AIE characteristics, size-selective molecular recognition, and theoretical calculations of rotary energy barrier. Because of the partially restricted TPE rotors, NUS-25 nanosheets are highly fluorescent. This property allows NUS-25 nanosheets to be used as a chemical sensor for the specific detection of acenaphthylene among a series of polycyclic aromatic hydrocarbons (PAHs) via fluorescent quenching mechanism. Further investigations show that NUS-25 nanosheets have much higher sensitivity and selectivity than their stacked bulk powder and other similar polymers containing dynamic TPE rotors. The highly efficient molecular recognition can be attributed to the photoinduced electron transfer (PET) from NUS-25 nanosheets to acenaphthylene, which is investigated by time-resolved photoluminescence measurements (TRPL), excitation and emission spectra, and density functional theory (DFT) calculations. Our findings demonstrate that confinement of AIE molecular rotors in 2D nanomaterials can enhance the molecular recognition. We anticipate that the material design strategy demonstrated in this study will inspire the development of other ultrathin 2D nanomaterials equipped with smart molecular machines for various applications.

Cotranslational chaperones, ubiquitous in all living organisms, protect nascent polypeptides from aggregation and facilitate their de novo folding. Importantly, emerging data have also suggested that ribosome-associated cotranslational chaperones have active regulatory roles in modulating protein translation. By characterizing the structure of a type of eukaryotic cotranslational chaperone, the ribosome-associated complex (RAC) from Saccharomyces cerevisiae, we show that RAC cross-links two ribosomal subunits, through a single long α-helix, to limit the predominant intersubunit rotation required for peptide elongation. We further demonstrate that any changes in the continuity, length or rigidity of this middle α-helix impair RAC function in vivo. Our results suggest a new mechanism in which RAC directly regulates protein translation by mechanically coupling cotranslational folding with the peptide-elongation cycle, and they lay the foundation for further exploration of regulatory roles of RAC in translation control.

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The self‐assembly of highly stable zirconium(IV)‐based coordination cages with aggregation induced emission (AIE) molecular rotors for in vitro bio‐imaging is reported. The two coordination cages, NUS‐100 and NUS‐101, are assembled from the highly stable trinuclear zirconium vertices and two flexible carboxyl‐decorated tetraphenylethylene (TPE) spacers. Extensive experimental and theoretical results show that the emissive intensity of the coordination cages can be controlled by restricting the dynamics of AIE‐active molecular rotors though multiple external stimuli. Because the two coordination cages have excellent chemical stability in aqueous solutions (pH stability: 2–10) and impressive AIE characteristics contributed by the molecular rotors, they can be employed as novel biological fluorescent probes for in vitro live‐cell imaging.