Jasmonoyl-isoleucine (JA-Ile) is a phytohormone that orchestrates plant defenses in response to wounding, feeding insects, or necrotrophic pathogens. JA-Ile metabolism has been studied intensively, but its catabolism as a potentially important mechanism for the regulation of JA-Ile–mediated signaling is not well-understood. Especially the enzyme(s) responsible for specifically glycosylating 12-hydroxy-jasmonic acid (12-OH-JA) and thereby producing 12-O-glucopyranosyl-jasmonic acid (12-O-Glc-JA) is still elusive. Here, we used co-expression analyses of available Arabidopsis thaliana transcriptomic data, identifying four UDP-dependent glycosyltransferase (UGT) genes as wound-induced and 12-OH-JA–related, namely, UGT76E1, UGT76E2, UGT76E11, and UGT76E12. We heterologously expressed and purified the corresponding proteins to determine their individual substrate specificities and kinetic parameters. We then used an ex vivo metabolite-fingerprinting approach to investigate these proteins in conditions as close as possible to their natural environment, with an emphasis on greatly extending the range of potential substrates. As expected, we found that UGT76E1 and UGT76E2 are 12-OH-JA-UGTs, with UGT76E1 contributing a major in vivo UGT activity, as deduced from Arabidopsis mutants with abolished or increased UGT gene expression. In contrast, recombinant UGT76E11 acted on an unidentified compound and also glycosylated two other oxylipins, 11-hydroxy-7,9,13-hexadecatrienoic acid (11-HHT) and 13-hydroxy-9,11,15-octadecatrienoic acid (13-HOT), which were also accepted by recombinant UGT76E1, UGT76E2, and UGT76E12 enzymes. UGT76E12 glycosylated 12-OH-JA only to a low extent, but also accepted an artificial hydroxylated fatty acid and low amounts of kaempferol. In conclusion, our findings have elucidated the missing step in the wound-induced synthesis of 12-O-glucopyranosyl-jasmonic acid in A. thaliana.
The receptor CRM1 is responsible for the nuclear export of many tumor-suppressor proteins and viral ribonucleoproteins. This renders CRM1 an interesting target for therapeutic intervention in diverse cancer types and viral diseases. Structural studies of Saccharomyces cerevisiae CRM1 ( Sc CRM1) complexes with inhibitors defined the molecular basis for CRM1 inhibition. Nevertheless, no structural information is available for inhibitors bound to human CRM1 ( Hs CRM1). Here, we present the structure of the natural inhibitor Leptomycin B bound to the Hs CRM1-RanGTP complex. Despite high sequence conservation and structural similarity in the NES-binding cleft region, Sc CRM1 exhibits 16-fold lower binding affinity than Hs CRM1 toward PKI-NES and significant differences in affinities toward potential CRM1 inhibitors. In contrast to Hs CRM1, competition assays revealed that a human adapted mutant Sc CRM1-T539C does not bind all inhibitors tested. Taken together, our data indicate the importance of using Hs CRM1 for molecular analysis and development of novel antitumor and antiviral drugs.
Many multicellular organisms specify germ cells during early embryogenesis by the inheritance of ribonucleoprotein (RNP) granules known as germplasm. However, the role of complex interactions of RNP granules during germ cell specification remains elusive. This study characterizes the interaction of RNP granules, Buc, and zebrafish Vasa (zfVasa) during germ cell specification. We identify a novel zfVasa-binding motif (Buc-VBM) in Buc and a Buc-binding motif (zfVasa-BBM) in zfVasa. Moreover, we show that Buc and zfVasa directly bind in vitro and that this interaction is independent of the RNA. Our circular dichroism spectroscopy data reveal that the intrinsically disordered Buc-VBM peptide forms alpha-helices in the presence of the solvent trifluoroethanol. Intriguingly, we further demonstrate that Buc-VBM enhances zfVasa ATPase activity, thereby annotating the first biochemical function of Buc as a zfVasa ATPase activator. Collectively, these results propose a model in which the activity of zfVasa is a central regulator of primordial germ cell (PGC) formation and is tightly controlled by the germplasm organizer Buc.
CRM1 is a nuclear export receptor that has been intensively targeted over the last decade for the development of antitumor and antiviral drugs. Structural analysis of several inhibitor compounds bound to CRM1 revealed that their mechanism of action relies on the covalent modification of a critical cysteine residue (Cys528 in the human receptor) located in the nuclear export signal-binding cleft. This study presents the crystal structure of human CRM1, covalently modified by 2-mercaptoethanol on Cys528, in complex with RanGTP at 2.58 Å resolution. The results demonstrate that buffer components can interfere with the characterization of cysteine-dependent inhibitor compounds.
I hereby declare that I prepared the doctoral thesis titled " Structure Based Search for Novel Nuclear Export Inhibiting Anti-Tumor Drugs" independently and with no sources and aids other than quoted. The thesis has not been submitted elsewhere.
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