The death inducing signaling complex (DISC) formed by the death receptor Fas, the adapter protein FADD and caspase-8 mediates the extrinsic apoptotic program. Mutations in Fas that disrupt the DISC cause autoimmune lymphoproliferative syndrome (ALPS). Here we show that the Fas–FADD death domain (DD) complex forms an asymmetric oligomeric structure composed of 5–7 Fas DD and 5 FADD DD, whose interfaces harbor ALPS-associated mutations. Structure-based mutations disrupt the Fas–FADD interaction in vitro and in living cells; the severity of a mutation correlates with the number of occurrence of a particular interaction in the structure. The highly oligomeric structure explains the requirement for hexameric or membrane-bound FasL in Fas signaling. It also predicts strong dominant negative effects of Fas mutations, which are confirmed by signaling assays. The structure optimally positions the FADD death effector domain (DED) to interact with the caspase-8 DED for caspase recruitment and higher order aggregation.

A system-level framework of complex microbe–microbe and host–microbe chemical cross-talk would help elucidate the role of our gut microbiota in health and disease. Here we report a literature-curated interspecies network of the human gut microbiota, called NJS16. This is an extensive data resource composed of ∼570 microbial species and 3 human cell types metabolically interacting through >4,400 small-molecule transport and macromolecule degradation events. Based on the contents of our network, we develop a mathematical approach to elucidate representative microbial and metabolic features of the gut microbial community in a given population, such as a disease cohort. Applying this strategy to microbiome data from type 2 diabetes patients reveals a context-specific infrastructure of the gut microbial ecosystem, core microbial entities with large metabolic influence, and frequently produced metabolic compounds that might indicate relevant community metabolic processes. Our network presents a foundation towards integrative investigations of community-scale microbial activities within the human gut.

An extension of directed evolution strategies to genome-wide variations increases the chance of obtaining metabolite-overproducing microbes. However, a general high-throughput screening platform for selecting improved strains remains out of reach. Here, to expedite the evolution of metabolite-producing microbes, we utilize synthetic RNA devices comprising a riboswitch and a selection module that specifically sense inconspicuous metabolites. Using L-lysine-producing Escherichia coli as a model system, we demonstrated that this RNA device could enrich pathway-optimized strains to up to 75% of the total population after four rounds of enrichment cycles. Furthermore, the potential applicability of this device was examined by successfully extending its application to the case of L-tryptophan. When used in conjunction with combinatorial mutagenesis for metabolite overproduction, our synthetic RNA device should facilitate strain improvement.

The control of viral outbreaks requires nucleic acid diagnostic tests that are sensitive, simple and fast. Here, we report a highly sensitive and specific one-pot assay for the fluorescence-based detection of RNA from pathogens. The assay, which can be performed within 30-50 min of incubation time and can reach a limit of detection of 0.1-attomolar RNA concentration, relies on a sustained isothermal reaction cascade producing an RNA aptamer that binds to a fluorogenic dye. The RNA aptamer is transcribed by the T7 RNA polymerase from the ligation product of a promoter DNA probe and a reporter DNA probe that hybridize with the target single-stranded RNA sequence via the SplintR ligase (a Chlorella virus DNA ligase). In 40 nasopharyngeal SARS-CoV-2 samples, the assay reached positive and negative predictive values of 95 and 100%, respectively. We also show that the assay can rapidly detect a range of viral and bacterial RNAs.

SEDL is an evolutionarily highly conserved protein in eukaryotic organisms. Deletions or point mutations in the SEDL gene are responsible for the genetic disease spondyloepiphyseal dysplasia tarda (SEDT), an X-linked skeletal disorder. SEDL has been identified as a component of the transport protein particle (TRAPP), critically involved in endoplasmic reticulum-to-Golgi vesicle transport. Herein, we report the 2.4 Å resolution structure of SEDL, which reveals an unexpected similarity to the structures of the N-terminal regulatory domain of two SNAREs, Ykt6p and Sec22b, despite no sequence homology to these proteins. The similarity and the presence of unusually many solvent-exposed apolar residues of SEDL suggest that it serves regulatory and/or adaptor functions through multiple protein-protein interactions. Of the four known missense mutations responsible for SEDT, three mutations (S73L, F83S, V130D) map to the protein interior, where the mutations would disrupt the structure, and the fourth (D47Y) on a surface at which the mutation may abrogate functional interactions with a partner protein.Intracellular targeting and fusion of transport vesicles in eukaryotes are tightly regulated to avoid inappropriate mixing of the contents in different compartments. Central components of the membrane fusion are the proteins denoted as SNAREs 1 (soluble N-ethylmaleimide-sensitive factor attachment receptor proteins). SNAREs constitute a superfamily of proteins that share a highly conserved sequence motif, the SNARE motif composed of 60 -70 amino acids (1). Most SNAREs are membrane proteins anchored on vesicular carriers (v-SNARE) and target organelles (t-SNARE) (1). Association of the SNARE domains between v-and t-SNAREs to form a helical bundle, termed the core complex (2), is believed to be the prime event that drives membrane fusion (3, 4). While the specific pairing of v-and t-SNAREs is one mechanism of providing the fidelity of membrane fusion, other proteins or protein complexes such as the transport protein particle (TRAPP) are known to provide further specificity by controlling the tethering process, in which a transport vesicle is properly docked on target membrane prior to pairing of SNAREs (5). TRAPP is localized to an early Golgi compartment (6) and is able to exchange the nucleotide of Ypt1p GTPase, which is an upstream event of v-and t-SNARE interactions (7,8). Recent in vitro transport studies showed that yeast TRAPP I binds COPII, the vesicle coat derived from the endoplasmic reticulum (ER), indicating that TRAPP I is the receptor for tethering COPII vesicles to Golgi membranes (6). The TRAPP complexes (TRAPP I and TRAPP II) are composed of 7-10 different polypeptides, which are highly conserved in evolution, with the yeast subunits sharing between 29 and 54% sequence identity with their human counterparts (9). The biochemical function of any of the constituent proteins is virtually unknown, although the TRAPP complex was shown to stimulate nucleotide exchange on the Ypt1p and the Ypt31/32 GTPases (10).Spond...

Coupling the energy of nucleoside triphosphate binding and hydrolysis to conformational changes is a common mechanism for a number of proteins with disparate cellular functions, including those involved in DNA replication, protein synthesis, and cell differentiation. Unique to this class of proteins is the dimeric Fe protein component of nitrogenase in which the binding and hydrolysis of MgATP controls intermolecular electron transfer and reduction of nitrogen to ammonia. In the work presented here, the MgADP-bound (or "off") conformational state of the nitrogenase Fe protein has been captured and a 2.15 A resolution X-ray crystal structure is presented. The structure described herein reveals likely mechanisms for long-range communication from the nucleotide-binding sites for controlling the affinity of association with the MoFe protein component. Two pathways, termed switches I and II, appear to be integral to this nucleotide signal transduction mechanism. In addition, the structure provides the basis for the changes in the biophysical properties of the [4Fe-4S] cluster observed when Fe protein binds nucleotides. The structure of the MgADP-bound Fe protein provides important insights into the respective contributions of nucleotide interaction and complex formation in defining the conformational states that are the keys to nitrogenase catalysis.

The structures of fully dehydrated, fully Cd 2+ -exchanged zeolite X, Cd 46 Si 100 Al 92 O 384 (Cd 46 -X; a ) 24.935(8) Å), and that of fully dehydrated Cd 2+ -and Tl + -exchanged zeolite X, Cd 24.5 Tl 43 Si 100 Al 92 O 384 (Cd 24.5 Tl 43 -X; a ) 24.858(9) Å), have been determined by single-crystal X-ray diffraction methods in the cubic space group Fd3 h at 21(1)°C. Cd 46 -X was prepared by ion exchange in a flowing stream of 0.05 M aqueous Cd(NO 3 ) 2 for 2 days. Cd 24.5 Tl 43 -X was prepared similarly using a solution 0.025 M each in Cd(NO 3 ) 2 and TlNO 3 . Each crystal was then dehydrated at 450°C and 2 × 10 -6 Torr for 2 days. Their structures were refined to the final error indices R 1 ) 0.055 and R 2 ) 0.077 with 544 reflections for Cd 46 -X, and R 1 ) 0.054 and R 2 ) 0.051 with 272 reflections for Cd 24.5 Tl 43 -X; I > 3σ(I). In the structure of dehydrated Cd 46 -X, Cd 2+ ions are located at two different crystallographic sites. Sixteen Cd 2+ ions fill site I, at the centers of the double sixrings; each Cd 2+ ion is octahedrally coordinated by framework oxygens, all at 2.35(1) Å. The remaining 30 Cd 2+ ions nearly fill the 32-fold site II in the single six-rings; each is three-coordinate planar to framework oxygens at 2.16(1) Å. The fractional occupancies in dehydrated Cd 24.5 Tl 43 -X are most easily explained with two types of unit cell: half have 14 Cd 2+ ions at site I and four Tl + ions at site I′; the remaining half have 15 Cd 2+ ions at site I and two Tl + ions at site I′. The remaining ten Cd 2+ ions occupy site II; 22 Tl + ions extend 1.52 Å into the supercage from their three oxygen planes to complete the filling of site II. The remaining 18 Tl + ions are statistically distributed over site III, a 48-fold equipoint in the supercages on twofold axes; Tl-O ) 2.79(2) Å. It appears that Cd 2+ ions prefer sites I and II in that order, and that Tl + ions occupy the remaining sites, except that they are too large to be stable at site I.

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