Wieden-Kothe, Ute

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Browsing Wieden-Kothe, Ute by Subject "Catalysis"

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    Archael proteins Nop10 and Gar1 increase the catalytic activity of Cbf5 in pseudouridylating tRNA
    (Nature Publishing Group, 2012) Kamalampeta, Rajashekhar; Wieden-Kothe, Ute
    Cbf5 is a pseudouridine synthase that usually acts in a guide RNA-dependent manner as part of H/ACA small ribonucleoproteins; however archaeal Cbf5 can also act independently of guide RNA in modifying uridine 55 in tRNA. This guide-independent activity of Cbf5 is enhanced by proteins Nop10 and Gar1 which are also found in H/ACA small ribonucleoproteins. Here, we analyzed the specific contribution of Nop10 and Gar1 for Cbf5-catalyzed pseudouridylation of tRNA. Interestingly, both Nop10 and Gar1 not only increase Cbf5’s affinity for tRNA, but they also directly enhance Cbf5’s catalytic activity by increasing the kcat of the reaction. In contrast to the guide RNA-dependent reaction, Gar1 is not involved in product release after tRNA modification. These results in conjunction with structural information suggest that Nop10 and Gar1 stabilize Cbf5 in its active conformation; we hypothesize that this might also be true for guide-RNA dependent pseudouridine formation by Cbf5.
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    An arginine-aspartate network in the active site of bacterial TruB is critical for catalyzing pseudouridine formation
    (Oxford University Press, 2014) Friedt, Jenna; Leavens, Fern M. V.; Mercier, Evan; Wieden, Hans-Joachim; Wieden-Kothe, Ute
    Pseudouridine synthases introduce the most common RNA modification and likely use the same catalytic mechanism. Besides a catalytic aspartate residue, the contributions of other residues for catalysis of pseudouridine formation are poorly understood. Here, we have tested the role of a conserved basic residue in the active site for catalysis using the bacterial pseudouridine synthase TruB targeting U55 in tRNAs. Substitution of arginine 181 with lysine results in a 2500-fold reduction of TruB’s catalytic rate without affecting tRNA binding. Furthermore, we analyzed the function of a second-shell aspartate residue (D90) that is conserved in all TruB enzymes and interacts with C56 of tRNA. Site-directed mutagenesis, biochemical and kinetic studies reveal that this residue is not critical for substrate binding but influences catalysis significantly as replacement of D90 with glutamate or asparagine reduces the catalytic rate 30- and 50-fold, respectively. In agreement with molecular dynamics simulations of TruB wild type and TruB D90N, we propose an electrostatic network composed of the catalytic aspartate (D48), R181 and D90 that is important for catalysis by finetuning the D48-R181 interaction. Conserved, negatively charged residues similar to D90 are found in a number of pseudouridine synthases, suggesting that this might be a general mechanism.