Structural and mechanistic insights into the biosynthesis of CDP-archaeol in membranes

The divergence of archaea, bacteria and eukaryotes was a fundamental step in evolution. One marker of this event is a major difference in membrane lipid chemistry between these kingdoms. Whereas the membranes of bacteria and eukaryotes primarily consist of straight fatty acids ester-bonded to glycerol-3-phosphate, archaeal phospholipids consist of isoprenoid chains ether-bonded to glycerol-1-phosphate. Notably, the mechanisms underlying the biosynthesis of these lipids remain elusive. Here, we report the structure of the CDP-archaeol synthase (CarS) of Aeropyrum pernix (ApCarS) in the CTP- and Mg(2+)-bound state at a resolution of 2.4 Å. The enzyme comprises a transmembrane domain with five helices and cytoplasmic loops that together form a large charged cavity providing a binding site for CTP. Identification of the binding location of CTP and Mg(2+) enabled modeling of the specific lipophilic substrate-binding site, which was supported by site-directed mutagenesis, substrate-binding affinity analyses, and enzyme assays. We propose that archaeol binds within two hydrophobic membrane-embedded grooves formed by the flexible transmembrane helix 5 (TM5), together with TM1 and TM4. Collectively, structural comparisons and analyses, combined with functional studies, not only elucidated the mechanism governing the biosynthesis of phospholipids with ether-bonded isoprenoid chains by CTP transferase, but also provided insights into the evolution of this enzyme superfamily from archaea to bacteria and eukaryotes.Cell Research advance online publication 29 September 2017; doi:10.1038/cr.2017.122

Crystal Structure of the Caenorhabditis elegans Apoptosome Reveals an Octameric Assembly of CED-4

SummaryThe CED-4 homo-oligomer or apoptosome is required for initiation of programmed cell death in Caenorhabditis elegans by facilitating autocatalytic activation of the CED-3 caspase zymogen. How the CED-4 apoptosome assembles and activates CED-3 remains enigmatic. Here we report the crystal structure of the complete CED-4 apoptosome and show that it consists of eight CED-4 molecules, organized as a tetramer of an asymmetric dimer via a previously unreported interface among AAA+ ATPases. These eight CED-4 molecules form a funnel-shaped structure. The mature CED-3 protease is monomeric in solution and forms an active holoenzyme with the CED-4 apoptosome, within which the protease activity of CED-3 is markedly stimulated. Unexpectedly, the octameric CED-4 apoptosome appears to bind only two, not eight, molecules of mature CED-3. The structure of the CED-4 apoptosome reveals shared principles for the NB-ARC family of AAA+ ATPases and suggests a mechanism for the activation of CED-3

Structural and Functional Insights into an Archaeal Lipid Synthase

The UbiA superfamily of intramembrane prenyltransferases catalyzes an isoprenyl transfer reaction in the biosynthesis of lipophilic compounds involved in cellular physiological processes. Digeranylgeranylglyceryl phosphate (DGGGP) synthase (DGGGPase) generates unique membrane core lipids for the formation of the ether bond between the glycerol moiety and the alkyl chains in archaea and has been confirmed to be a member of the UbiA superfamily. Here, the crystal structure is reported to exhibit nine transmembrane helices along with a large lateral opening covered by a cytosolic cap domain and a unique substrate-binding central cavity. Notably, the lipid-bound states of this enzyme demonstrate that the putative substrate-binding pocket is occupied by the lipidic molecules used for crystallization, indicating the binding mode of hydrophobic substrates. Collectively, these structural and functional studies provide not only an understanding of lipid biosynthesis by substrate-specific lipid-modifying enzymes but also insights into the mechanisms of lipid membrane remodeling and adaptation

Correction:Structural and Functional Insights into an Archaeal Lipid Synthase

(Cell Reports 33, 108294-1–9.e1–e4; October 20, 2020) In the originally published version of this article, the supplemental information file containing Figures S1–S7 and Table S1 was inadvertently removed. The complete supplemental information file is now included with the paper online. The production team regrets this error

The molecular mechanism of Xiaoxuming decoction in the treatment of ischemic stroke based on network pharmacology and molecular docking

Abstract Xiaoxuming decoction is a traditional Chinese medicine that has been widely used in the clinical treatment of ischemic stroke (IS). This study employed network pharmacology to identify the bioactive molecules and therapeutic mechanism of Xiaoxuming decoction against IS. First, the traditional Chinese medicine systems pharmacology database and analysis platform (TCMSP) was utilized to obtain the ingredients and potential target proteins related to IS in the Xiaoxuming decoction. Subsequently, known target proteins related to IS were collected from online Mendelian inheritance in man (OMIM), Disgenet, and Gencards databases. The mechanism of Xiaoxuming decoction against IS was identified by enrichment analysis of gene ontology (GO) and Kyoto Encyclopedia of genes and genomes (KEGG). Additionally, protein–protein interaction data were obtained from the search tool for the retrieval of interacting genes/proteins (STRING). The hub gene was further screened out from the gene expression omnibus (GEO) and verified by molecular docking. The study identified a total of 183 candidate molecules and 140 targets related to IS. These candidate targets regulate biological processes including inflammation, autophagy, oxidative stress, and vascular reaction. Our findings provide a comprehensive demonstration of the active compounds, key targets, main signaling pathways, and underlying molecular mechanisms of Xiaoxuming decoction in treating IS

Ultrafast selective adsorption of pretreatment inhibitors from lignocellulosic hydrolysate with metal-organic frameworks: Performance and adsorption mechanisms

In this work, four metal-organic frameworks materials (MOFs, MIL-140A, MIL-140C, MIL-101(Fe) and NH2-MIL-101(Fe) were prepared, characterized and compared for the adsorptive removal of furfural and four phenolic inhibitors. MIL-140C demonstrated the best adsorption capability among the tested MOFs. Effects of pH, ionic strength, contact time, adsorbent dosage, temperature and sugars on adsorption of inhibitors on MIL-140C were systematically investigated. Inhibitors adsorption was ultrafast within minutes and kinetic data fitted pseudosecond-order model well. The Langmuir isotherm described the adsorption process satisfactorily with maximum adsorption capacities of 222.72, 240.38, 231.48, 207.04 and 60.79 mg/g for vanillin, syringaldehyde, ferulic acid, p-coumaric acid and furfural, respectively. Thermodynamic parameters disclosed that nature of the adsorption was exothermic and spontaneous under the experimental conditions. MIL-140C demonstrated exceptional adsorption selectivity towards inhibitors even with excessive amount of xylose and glucose, as well as excellent regeneration performance after five adsorption/desorption cycles. MIL-140C also exhibited satisfactory detoxification performance after treatment of real corn stover dilute acid hydrolysate. Furthermore, analysis of underlying adsorption mechanism showed that pi-pi interaction, hydrophobic interaction and hydrogen bonding/metal-coordination (depending on solution pH) were involved in the adsorption of tested phenolic inhibitors, while the pi-pi and hydrophobic interactions contributed to the furfural adsorption. The overall results revealed that MIL-140C could hold great promise in removing phenolic and furan inhibitors from lignocellulosic hydrolysate

Structural and biochemical basis for ubiquitin ligase recruitment by arrestin-related domain-containing protein-3 (ARRDC3).

After protracted stimulation, the β2-adrenergic receptor and many other G-protein-coupled receptors are ubiquitinated and down-regulated. Arrestin-related domain-containing protein-3 (ARRDC3) has been proposed to recruit the ubiquitin ligase Nedd4 to the β2-adrenergic receptor. ARRDC3 contains two PPXY motifs that could potentially interact with any of the four WW domains of Nedd4. Here we dissect the interaction determinants. ARRDC3 PPXY-Nedd4 WW dissociation constants vary from unmeasurable to Kd = 3 μM for the third WW domain of Nedd4 binding to the first PPXY motif of ARRDC3. Structures of the uncomplexed and PPXY1-bound WW3 domain were determined at 1.1 and 1.7 Å resolution. The structures revealed conformational changes upon binding and the hydrogen bonding network in exquisite detail. Tight packing of ARRDC3 Val-352', part of a 310 helix at the C terminus of PPXY1, is important for high affinity binding to WW3. Although no single WW domain is strictly essential for the binding of Nedd4 and ARRDC3 expressed in HEK293 cells, high affinity binding of full-length ARRDC3 and Nedd4 is driven by the avid interaction of both PPXY motifs with either the WW2-WW3 or WW3-WW4 combinations, with Kd values as low as 300 nM