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  • Brassinosteroid signaling and BRI1 dynamics went underground.

    21 septembre, par Jaillais Y, Vert G
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    Brassinosteroid signaling and BRI1 dynamics went underground.

    Curr Opin Plant Biol. 2016 Oct;33:92-100

    Authors: Jaillais Y, Vert G

    Abstract
    Brassinosteroids (BRs) are a group of steroid molecules perceived at the cell surface and that act as plant hormones. Since their discovery as crucial growth substances, BRs were mainly studied for their action in above ground organs and the BR signaling pathway was largely uncovered in the context of hypocotyl elongation. However, for the past two years, most of the exciting findings on BR signaling have been made using roots as a model. The Arabidopsis root is a system of choice for cell biology and allowed detailed characterization of BR perception at the cell membrane. In addition, a series of elegant articles dissected how BRs act in tissue specific manners to control root growth and development.

    PMID: 27419885 [PubMed - indexed for MEDLINE]

  • Endoplasmic Reticulum Transport of Glutathione by Sec61 Is Regulated by Ero1 and Bip.

    19 septembre, par Ponsero AJ, Igbaria A, Darch MA, Miled S, Outten CE, Winther JR, Palais G, D'Autréaux B, Delaunay-Moisan A, Toledano MB
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    Endoplasmic Reticulum Transport of Glutathione by Sec61 Is Regulated by Ero1 and Bip.

    Mol Cell. 2017 Sep 11;:

    Authors: Ponsero AJ, Igbaria A, Darch MA, Miled S, Outten CE, Winther JR, Palais G, D'Autréaux B, Delaunay-Moisan A, Toledano MB

    Abstract
    In the endoplasmic reticulum (ER), Ero1 catalyzes disulfide bond formation and promotes glutathione (GSH) oxidation to GSSG. Since GSSG cannot be reduced in the ER, maintenance of the ER glutathione redox state and levels likely depends on ER glutathione import and GSSG export. We used quantitative GSH and GSSG biosensors to monitor glutathione import into the ER of yeast cells. We found that glutathione enters the ER by facilitated diffusion through the Sec61 protein-conducting channel, while oxidized Bip (Kar2) inhibits transport. Increased ER glutathione import triggers H2O2-dependent Bip oxidation through Ero1 reductive activation, which inhibits glutathione import in a negative regulatory loop. During ER stress, transport is activated by UPR-dependent Ero1 induction, and cytosolic glutathione levels increase. Thus, the ER redox poise is tuned by reciprocal control of glutathione import and Ero1 activation. The ER protein-conducting channel is permeable to small molecules, provided the driving force of a concentration gradient.

    PMID: 28918898 [PubMed - as supplied by publisher]

  • Pseudolysogeny and sequential mutations build multiresistance to virulent bacteriophages in Pseudomonas aeruginosa.

    16 septembre, par Latino L, Midoux C, Hauck Y, Vergnaud G, Pourcel C
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    Pseudolysogeny and sequential mutations build multiresistance to virulent bacteriophages in Pseudomonas aeruginosa.

    Microbiology. 2016 May;162(5):748-63

    Authors: Latino L, Midoux C, Hauck Y, Vergnaud G, Pourcel C

    Abstract
    Coevolution between bacteriophages (phages) and their prey is the result of mutualistic interactions. Here, we show that pseudolysogeny is a frequent outcome of infection by virulent phages of Pseudomonas aeruginosa and that selection of resistant bacterial mutants is favoured by continuous production of phages. We investigated the frequency and characteristics of P. aeruginosa strain PAO1 variants resisting infection by different combinations of virulent phages belonging to four genera. The frequency of resistant bacteria was 10- 5 for single phage infection and 10- 6 for infections with combinations of two or four phages. The genome of 27 variants was sequenced and the comparison with the genome of the parental PAO1 strain allowed the identification of point mutations or small indels. Four additional variants were characterized by a candidate gene approach. In total, 27 independent mutations were observed affecting 14 genes and a regulatory region. The mutations affected genes involved in biosynthesis of type IV pilus, alginate, LPS and O-antigen. Half of the variants possessed changes in homopolymer tracts responsible for frameshift mutations and these phase variation mutants were shown to be unstable. Eleven double mutants were detected. The presence of free phage DNA was observed in association with exclusion of superinfection in half of the variants and no chromosomal mutation could be found in three of them. Upon further growth of these pseudolysogens, some variants with new chromosomal mutations were recovered, presumably due to continuous evolutionary pressure.

    PMID: 26921273 [PubMed - indexed for MEDLINE]

  • Trz1, the long form RNase Z from yeast, forms a stable heterohexamer with endonuclease Nuc1 and mutarotase.

    14 septembre, par Ma M, Li de La Sierra Gallay I, Lazar N, Pellegrini O, Lepault J, Condon C, Durand D, van Tilbeurgh H
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    Trz1, the long form RNase Z from yeast, forms a stable heterohexamer with endonuclease Nuc1 and mutarotase.

    Biochem J. 2017 Sep 12;:

    Authors: Ma M, Li de La Sierra Gallay I, Lazar N, Pellegrini O, Lepault J, Condon C, Durand D, van Tilbeurgh H

    Abstract
    Proteomic studies haves established that Trz1, Nuc1 and mutarotase form a complex in yeast. Trz1 is a b-lactamase type RNase composed of two b-lactamase type domains connected by a long linker that is responsible for the endonucleolytic cleavage at the 3'-end of tRNAs during the maturation process (RNase Z activity); Nuc1 is a dimeric mitochondrial nuclease involved in apoptosis, while mutarotase (encoded by YMR099C) catalyzes the conversion between the a- and b-configuration of glucose-6-phosphate. Using gel-filtration, SAXS and electron microscopy we demonstrated that Trz1, Nuc1 and mutarotase form a very stable heterohexamer, composed of two copies of each of the three subunits. A Nuc1 homodimer is at the centre of the complex, creating a two-fold symmetry and interacting with both Trz1 and mutarotase. Enzymatic characterization of the ternary complex revealed that the activities of Trz1 and mutarotase are not affected by complex formation, but that the Nuc1 activity is completely inhibited by mutarotase and partially by Trz1. This suggests that mutarotase and Trz1 might be regulators of the Nuc1 apoptotic nuclease activity.

    PMID: 28899942 [PubMed - as supplied by publisher]

  • Ultrafast flavin photoreduction in an oxidized animal (6-4) photolyase through an unconventional tryptophan tetrad.

    12 septembre, par Martin R, Lacombat F, Espagne A, Dozova N, Plaza P, Yamamoto J, Müller P, Brettel K, de la Lande A
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    Ultrafast flavin photoreduction in an oxidized animal (6-4) photolyase through an unconventional tryptophan tetrad.

    Phys Chem Chem Phys. 2017 Sep 11;:

    Authors: Martin R, Lacombat F, Espagne A, Dozova N, Plaza P, Yamamoto J, Müller P, Brettel K, de la Lande A

    Abstract
    Photolyases are flavoenzymes repairing UV-induced lesions in DNA, which may be activated by a photoreduction of their FAD cofactor. In most photolyases, this photoreduction proceeds by electron transfer along a chain of three tryptophan (Trp) residues, connecting the flavin to the protein surface. Much less studied, animal (6-4) photolyases (repairing pyrimidine-pyrimidone (6-4) photoproducts) are particularly interesting as they were recently shown to have a longer electron transfer chain, counting four Trp residues. Using femtosecond polarized transient absorption spectroscopy, we performed a detailed analysis of the photoactivation reaction in the (6-4) photolyase of Xenopus laevis with oxidized FAD. We showed that the excited flavin is very quickly reduced (∼0.5 ps) by a nearby tryptophan residue, yielding FAD˙(-) and WH˙(+) radicals. Subsequent kinetic steps in the picosecond regime were assigned to the migration of the positive charge along the Trp tetrad, in competition with charge recombination. We propose that the positive charge is actually delocalized over various Trp residues during most of the dynamics and that charge recombination essentially occurs through the proximal tryptophanyl radical. Oxidation of the fourth tryptophan is thought to be reached about as fast as that of the third one (∼40 ps), based on a comparison with a mutant protein lacking the distal Trp, implying ultrafast electron transfer between these two residues. This unusual mechanism sheds light on the rich diversity of electron transfer pathways found in various photolyases, and evolution-related cryptochromes alike.

    PMID: 28890968 [PubMed - as supplied by publisher]

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