Hormaomycin produced by Streptomyces griseoflavus is a structurally highly modified depsipeptide that contains several unique building blocks with cyclopropyl, nitro, and chlorine moieties. Within the genus Streptomyces, it acts as a bacterial hormone that induces morphological differentiation and the production of bioactive secondary metabolites. In addition, hormaomycin is an extremely potent narrow-spectrum antibiotic. In this study, we shed light on hormaomycin biosynthesis by a combination of feeding studies, isolation of the biosynthetic nonribosomal peptide synthetase (NRPS) gene cluster, and in vivo and in vitro functional analysis of enzymes. In addition, several nonnatural hormaomycin congeners were generated by feeding-induced metabolic rerouting. The NRPS contains numerous highly repetitive regions that suggest an evolutionary scenario for this unusual bacterial hormone, providing new opportunities for evolution-inspired metabolic engineering of novel nonribosomal peptides. 相似文献
During the investigation of the phosphate bronzes (PO2)4(WO3)2m [MPTBP] and Kx(P2O4)2WO3)2m [DPTBH] crystals of a new type were observed. HREM images of these crystals showed twinned ReO3-type slabs the junction of which was parallel to the (102)ReO3 plane. The proposed model identified the twin boundary as built from P2O7 groups involving the formation of pentagonal tunnels. The structure of this new type of extended defects is quite original: it corresponds to a new structural type named “diphosphate tungsten bronzes with pentagonal tunnels” [DPTBP], for which no regular member could be synthesized. Image calculations were performed to confirm the junction model. Apart from the disordered stacking of the ReO3-type slabs, very few defects were observed and shear planes were only obtained in reduced samples. This new structural type takes its place in the large family of phosphate tungsten bronzes where all members (DPTBH, MPTBH, MPTBP) are very closely related. 相似文献
Amphiphilic hairy nanoparticles are prepared in a one step, batch, heterogeneous polymerization of styrene or n-butyl acrylate, using a water-soluble poly(sodium acrylate) alkoxyamine macroinitiator based on the SG1 nitroxide. 相似文献
Silica-supported heteropoly acids have been studied by microcalorimetry. The results are greatly dependent on both the activation temperature and the heteropoly acid, in agreement with the n-hexane cracking experiments. It is shown that very strong acid sites are formed on H4SiW12O40/SiO2 activated at 623 K and on H3PW12O40/SiO2 activated at 423 K. 相似文献
Structured hybrid nanoparticles were synthesized via surface‐initiated atom transfer radical polymerization of MMA from ordered mesoporous silica (OMS) nanoparticles with various morphologies. The design of the OMS particles was adjusted to target either spherical core‐shell or cylindrical morphologies with a mean diameter below 400 nm. The polymer growth via ATRP from the silica surface was well‐controlled as demonstrated by the macromolecular characteristics of the grafted chains. Original hybrid multilayered nanoparticles composed of either a dense silica core or hollow core; an inner OMS shell showing radial orientation of the mesopores and an outer PMMA shell with controlled thickness were successfully prepared.
Amphipathic agents are widely used in various fields including biomedical sciences. Micelle-forming detergents are particularly useful for in vitro membrane-protein characterization. As many conventional detergents are limited in their ability to stabilize membrane proteins, it is necessary to develop novel detergents to facilitate membrane-protein research. In the current study, we developed novel trimaltoside detergents with an alkyl pendant-bearing terphenyl unit as a hydrophobic group, designated terphenyl-cored maltosides (TPMs). We found that the geometry of the detergent hydrophobic group substantially impacts detergent self-assembly behavior, as well as detergent efficacy for membrane-protein stabilization. TPM-Vs, with a bent terphenyl group, were superior to the linear counterparts (TPM-Ls) at stabilizing multiple membrane proteins. The favorable protein stabilization efficacy of these bent TPMs is likely associated with a binding mode with membrane proteins distinct from conventional detergents and facial amphiphiles. When compared to n-dodecyl-β-d -maltoside (DDM), most TPMs were superior or comparable to this gold standard detergent at stabilizing membrane proteins. Notably, TPM-L3 was particularly effective at stabilizing the human β2 adrenergic receptor (β2AR), a G-protein coupled receptor, and its complex with Gs protein. Thus, the current study not only provides novel detergent tools that are useful for membrane-protein study, but also suggests a critical role for detergent hydrophobic group geometry in governing detergent efficacy. 相似文献
Consider an elastic thin three-dimensional body made of a periodic distribution of elastic inclusions. When both the thickness of the beam and the size of the heterogeneities tend simultaneously to zero the authors obtain three different one-dimensional models of beam depending upon the limit of the ratio of these two small parameters. 相似文献