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…
Allene oxide cyclase (EC 5.3.99.6) catalyzes the stereospecific cyclization of an unstable allene oxide to (9S,13S)-12-oxo-(10,15Z)-phytodienoic acid, the ultimate precursor of jasmonic acid. This dimeric enzyme has previously been purified, and two almost identical N-terminal peptides were found, suggesting allene oxide cyclase to be a homodimeric protein. Furthermore, the native protein was N-terminally processed. Using degenerate primers, a polymerase chain reaction fragment could be generated from tomato, which was further used to isolate a full-length cDNA clone of 1 kilobase pair coding for a protein of 245 amino acids with a molecular mass of 26 kDa. Whereas expression of the whole coding region failed to detect allene oxide cyclase activity, a 5′-truncated protein showed high activity, suggesting that additional amino acids impair the enzymatic function. Steric analysis of the 12-oxophytodienoic acid formed by the recombinant enzyme revealed exclusive (>99%) formation of the 9S,13Senantiomer. Exclusive formation of this enantiomer was also found in wounded tomato leaves. Southern analysis and genetic mapping revealed the existence of a single gene for allene oxide cyclase located on chromosome 2 of tomato. Inspection of the N terminus revealed the presence of a chloroplastic transit peptide, and the location of allene oxide cyclase protein in that compartment could be shown by immunohistochemical methods. Concomitant with the jasmonate levels, the accumulation of allene oxide cyclase mRNA was transiently induced after wounding of tomato leaves.
Publikation
Wrenger, S.; Faust, J.; Mrestani-Klaus, C.; Fengler, A.; Stöckel-Maschek, A.; Lorey, S.; Kähne, T.; Brandt, W.; Neubert, K.; Ansorge, S.; Reinhold, D.;Down-regulation of T Cell Activation following Inhibition of Dipeptidyl Peptidase IV/CD26 by the N-terminal Part of the Thromboxane A2 ReceptorJ. Biol. Chem.27522180-22186(2000)DOI: 10.1074/jbc.M002338200
Using synthetic inhibitors, it has been shown that the ectopeptidase dipeptidyl peptidase IV (DP IV) (CD26) plays an important role in the activation and proliferation of T lymphocytes. The human immunodeficiency virus-1 Tat protein, as well as the N-terminal nonapeptide Tat(1–9) and other peptides containing the N-terminal sequence XXP, also inhibit DP IV and therefore T cell activation. Studying the effect of amino acid exchanges in the N-terminal three positions of the Tat(1–9) sequence, we found that tryptophan in position 2 strongly improves DP IV inhibition. NMR spectroscopy and molecular modeling show that the effect of Trp2-Tat(1–9) could not be explained by significant alterations in the backbone structure and suggest that tryptophan enters favorable interactions with DP IV. Data base searches revealed the thromboxane A2 receptor (TXA2-R) as a membrane protein extracellularly exposing N-terminal MWP. TXA2-R is expressed within the immune system on antigen-presenting cells, namely monocytes. The N-terminal nonapeptide of TXA2-R, TXA2-R(1–9), inhibits DP IV and DNA synthesis and IL-2 production of tetanus toxoid-stimulated peripheral blood mononuclear cells. Moreover, TXA2-R(1–9) induces the production of the immunosuppressive cytokine transforming growth factor-β1. These data suggest that the N-terminal part of TXA2-R is an endogenous inhibitory ligand of DP IV and may modulate T cell activation via DP IV/CD26 inhibition.