Unser 10. Leibniz Plant Biochemistry Symposium am 7. und 8. Mai war ein großer Erfolg. Thematisch ging es in diesem Jahr um neue Methoden und Forschungsansätze der Naturstoffchemie. Die exzellenten Vorträge über Wirkstoffe…
Omanische Heilpflanze im Fokus der Phytochemie IPB-Wissenschaftler und Partner aus Dhofar haben jüngst die omanische Heilpflanze Terminalia dhofarica unter die phytochemische Lupe genommen. Die Pflanze ist reich an…
Geschmack ist vorhersagbar: Mit FlavorMiner. FlavorMiner heißt das Tool, das IPB-Chemiker und Partner aus Kolumbien jüngst entwickelt haben. Das Programm kann, basierend auf maschinellem Lernen (KI), anhand der…
The formation of phytochelatins, small metal‐binding glutathione‐derived peptides, is one of the well‐studied responses of plants to toxic metal exposure. Phytochelatins have also been detected in some fungi and some marine diatoms. Genes encoding phytochelatin synthases (PCS) have recently been cloned from Arabidopsis , wheat and Schizosaccharomyces pombe . Surprisingly, database searches revealed the presence of a homologous gene in the Caenorhabditis elegans genome, DDBJ/EMBL/GenBank accession no. 266513. Here we show that C. elegans indeed expresses a gene coding for a functional phytochelatin synthase. CePCS complements the Cd2+ sensitivity of a Schizosaccharomyces pombe PCS knock‐out strain and confers phytochelatin synthase activity to these cells. Thus, phytochelatins may play a role for metal homeostasis also in certain animals.
Publikation
Brandt, W.; Golbraikh, A.; Tager, M.; Lendeckel, U.;A molecular mechanism for the cleavage of a disulfide bond as the primary function of agonist binding to G-protein-coupled receptors based on theoretical calculations supported by experimentsEur. J. Biochem.26189-97(1999)DOI: 10.1046/j.1432-1327.1999.00224.x
A model of the binding site of δ‐opioids in the extracellular region of the G‐protein‐coupled opioid receptor based on modelling studies is presented. The distance between Asp288 and the disulfide bridge (Cys121–Cys198) formed between the first and second extracellular loops was found to be short. This model is consistent with site‐directed mutagenesis studies. The arrangement of the ligands found in the receptor led to the development of a reaction mechanism for the cleavage of the disulfide bond catalysed by the ligands. Semi‐empirical quantum chemical PM3 and AM1 calculations as well as ab initio studies showed that the interaction between the carboxylic acid side chain of aspartic acid and the disulfide bond leads to the polarization of, and withdrawal of a proton from, the protonated nitrogen of the ligand to one of the sulfur atoms. A mixed sulfenic acid and carboxylic acid anhydrate is formed as an intermediate as well as a thiol. The accompanying cleavage of the disulfide bond may produce a conformational change in the extracellular loops such that the pore formed by the seven‐helix bundle opens allowing entrance of the ligand, water and ions into the cell. Cleavage of the disulfide bond after opioid administration was demonstrated experimentally by flow‐cytometric measurements employing CMTMR and monobromobimane‐based analyses of membrane‐located thiols. The suggested mechanism may explain, in a consistent way, the action of agonists and antagonists and is assumed to be common for many G‐protein coupled receptors.
Publikation
Vörös, K.; Feussner, I.; Kühn, H.; Lee, J.; Graner, A.; Löbler, M.; Parthier, B.; Wasternack, C.;Characterization of a methyljasmonate-inducible lipoxygenase from barley (Hordeum vulgare cv. Salome) leavesEur. J. Biochem.25136-44(1998)DOI: 10.1046/j.1432-1327.1998.2510036.x
We found three methyl jasmonate−induced lipoxygenases with molecular masses of 92 kDa, 98 kDa, and 100 kDa (LOX‐92, ‐98 and ‐100) [Feussner, I., Hause, B., Vörös, K., Parthier, B. & Wasternack, C. (1995) Plant J. 7 , 949−957]. At least two of them (LOX‐92 and LOX‐100), were shown to be localized within chloroplasts of barley leaves. Here, we describe the isolation of a cDNA (3073 bp) coding for LOX‐100, a protein of 936 amino acid residues and a molecular mass of 106 kDa. By sequence comparison this lipoxygenase could be identified as LOX2‐type lipoxygenase and was therefore designated LOX2 : Hv : 1 . The recombinant lipoxygenase was expressed in Escherichia coli and characterized as linoleate 13‐LOX and arachidonate 15‐LOX, respectively. The enzyme exhibited a pH optimum around pH 7.0 and a moderate substrate preference for linoleic acid. The gene was transiently expressed after exogenous application of jasmonic acid methyl ester with a maximum between 12 h and 18 h. Its expression was not affected by exogenous application of abscisic acid. Also a rise of endogenous jasmonic acid resulting from sorbitol stress did not induce LOX2 : Hv : 1 , suggesting a separate signalling pathway compared with other jasmonate‐induced proteins of barley. The properties of LOX2 : Hv : 1 are discussed in relation to its possible involvement in jasmonic acid biosynthesis and other LOX forms of barley identified so far.