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Bibenzyls are a specialized metabolite class found throughout the plant kingdom. One of the most prolific producers of bibenzyls are liverworts, specifically plants of the Radula genera. These plants possess an incredible diversity of bibenzyls, prenylated bibenzyls, and a few (bis)bibenzyls, several of which have medicinal properties, including perrottetinene, an analog of tetrahydrocannabinol from cannabis. To provide insight into the bibenzyls’ biosynthesis in planta, exogenous phytohormones were applied to in vitro grown Radula complanata and bibenzyl metabolite production was monitored with targeted and untargeted metabolomics. The targeted metabolomic analysis of six prenylated bibenzyls revealed that production of these metabolites was largely reduced when plants were treated with abscisic acid (AA), salicylic acid (SA), 1-naphthaleneacetic acid (NAA), or 6-benzylaminopurine (BAP). The reduction of these metabolites in the BAP and NAA treatment suggests that prenylated bibenzyl production is negatively correlated with vegetative plant growth. The reduction of bibenzyls at low AA and SA concentrations and mild increase at higher AA and SA concentrations suggest that their production is regulated by these stress hormones. In addition, six other bibenzyl metabolites were tentatively identified from the untargeted analysis. These results provide insight into the influence of phytohormones on the bioactive bibenzyl content of R. complanata.
Publikation
MqnA, the only chorismate dehydratase known so far, catalyzes the initial step in the biosynthesis of menaquinone via the futalosine pathway. Details of the MqnA reaction mechanism remain unclear. Here, we present crystal structures of Streptomyces coelicolor MqnA and its active site mutants in complex with chorismate and the product 3-enolpyruvyl-benzoate, produced during heterologous expression in Escherichia coli. Together with activity studies, our data are in line with dehydration proceeding via substrate assisted catalysis, with the enol pyruvyl group of chorismate acting as catalytic base. Surprisingly, structures of the mutant Asn17Asp with copurified ligand suggest that the enzyme converts to a hydrolase by serendipitous positioning of the carboxyl group. All complex structures presented here exhibit a closed Venus flytrap fold, with the enzyme exploiting the characteristic ligand binding properties of the fold for specific substrate binding and catalysis. The conformational rearrangements that facilitate complete burial of substrate/product, with accompanying topological changes to the enzyme surface, could foster substrate channeling within the biosynthetic pathway.
Publikation
Access to inorganic phosphate (Pi), a principal intermediate of energy and nucleotide metabolism, profoundly affects cellular activities and plant performance. In most soils, antagonistic Pi-metal interactions restrict Pi bioavailability, which guides local root development to maximize Pi interception. Growing root tips scout the essential but immobile mineral nutrient; however, the mechanisms monitoring external Pi sta-tus are unknown. Here, we show that Arabidopsis LOW PHOSPHATE ROOT 1 (LPR1), one key determinant of Fe-dependent Pi sensing in root meristems, encodes a novel ferroxidase of high substrate specificity and affinity (apparent KM ∼2 μmM Fe2+). LPR1 typifies an ancient, Fe-oxidizing multicopper protein family that evolved early upon bacterial land colonization. The ancestor of streptophyte algae and embryophytes (land plants) acquired LPR1-type ferroxidase from soil bacteria via horizontal gene transfer, a hypothesis supported by phylogenomics, homology modeling, and biochemistry. Our molecular and kinetic data on LPR1 regulation indicate that Pi-dependent Fe substrate availability determines LPR1 activity and function. Guided by the metabolic lifestyle of extant sister bacterial genera, we propose that Arabidopsis LPR1 monitors subtle concentration differentials of external Fe availability as a Pi-dependent cue to adjust root meristem maintenance via Fe redox signaling and cell wall modification. We further hypothesize that the acquisition of bacterial LPR1-type ferroxidase by embryophyte progenitors facilitated the evolution of local Pi sensing and acquisition during plant terrestrialization.