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Unfolded Protein Response Suppression in Yeast by Loss of tRNA Modifications.

ABSTRACT: Modifications in the anticodon loop of transfer RNAs (tRNAs) have been shown to ensure optimal codon translation rates and prevent protein homeostasis defects that arise in response to translational pausing. Consequently, several yeast mutants lacking important anticodon loop modifications were shown to accumulate protein aggregates. Here we analyze whether this includes the activation of the unfolded protein response (UPR), which is commonly triggered by protein aggregation within the endoplasmic reticulum (ER). We demonstrate that two different aggregation prone tRNA modification mutants (elp6 ncs2; elp3 deg1) lacking combinations of 5-methoxycarbonylmethyl-2-thiouridine (mcm?s²U: elp3; elp6; ncs2) and pseudouridine (?: deg1) reduce, rather than increase, splicing of HAC1 mRNA, an event normally occurring as a precondition of UPR induction. In addition, tunicamycin (TM) induced HAC1 splicing is strongly impaired in the elp3 deg1 mutant. Strikingly, this mutant displays UPR independent resistance against TM, a phenotype we found to be rescued by overexpression of tRNA^Gln(UUG), the tRNA species usually carrying the mcm?s²U34 and ?38 modifications. Our data indicate that proper tRNA anticodon loop modifications promote rather than impair UPR activation and reveal that protein synthesis and homeostasis defects in their absence do not routinely result in UPR induction but may relieve endogenous ER stress.

SUBMITTER: Bruch A

PROVIDER: S-EPMC6275073 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature

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Unfolded Protein Response Suppression in Yeast by Loss of tRNA Modifications.

Bruch Alexander A Klassen Roland R Schaffrath Raffael R

Genes 20181023 11

Modifications in the anticodon loop of transfer RNAs (tRNAs) have been shown to ensure optimal codon translation rates and prevent protein homeostasis defects that arise in response to translational pausing. Consequently, several yeast mutants lacking important anticodon loop modifications were shown to accumulate protein aggregates. Here we analyze whether this includes the activation of the unfolded protein response (UPR), which is commonly triggered by protein aggregation within the endoplasm ...[more]

PMID: 30360492

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Project description:Modified nucleotides are prevalent in tRNA. Experimental studies reveal that these covalent modifications play an important role in tuning tRNA function. In this study, molecular dynamics (MD) simulations were used to investigate how modifications alter tRNA dynamics. The X-ray crystal structures of tRNA(Asp), tRNA(Phe), and tRNA(iMet), both with and without modifications, were used as initial structures for 333 ns explicit solvent MD simulations with AMBER. For each tRNA molecule, three independent trajectory calculations were performed, giving an aggregate of 6 μs of total MD across six molecules. The global root-mean-square deviations (RMSD) of atomic positions show that modifications only introduce significant rigidity to the global structure of tRNA(Phe). Interestingly, RMSDs of the anticodon stem-loop (ASL) suggest that modified tRNA has a more rigid structure compared to the unmodified tRNA in this domain. The anticodon RMSDs of the modified tRNAs, however, are higher than those of corresponding unmodified tRNAs. These findings suggest that the rigidity of the anticodon stem-loop is finely tuned by modifications, where rigidity in the anticodon arm is essential for tRNA translocation in the ribosome, and flexibility of the anticodon is important for codon recognition. Sugar pucker and water residence time of pseudouridines in modified tRNAs and corresponding uridines in unmodified tRNAs were assessed, and the results reinforce that pseudouridine favors the 3'-endo conformation and has a higher tendency to interact with water. Principal component analysis (PCA) was used to examine correlated motions in tRNA. Additionally, covariance overlaps of PCAs were compared for trajectories of the same molecule and between trajectories of modified and unmodified tRNAs. The comparison suggests that modifications alter the correlated motions. For the anticodon bases, the extent of stacking was compared between modified and unmodified molecules, and only unmodified tRNA(Asp) has significantly higher percentage of stacking time. Overall, the simulations reveal that the effect of covalent modification on tRNA dynamics is not simple, with modifications increasing flexibility in some regions of the structure and increasing rigidity in other regions.

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Unfolded Protein Response Suppression in Yeast by Loss of tRNA Modifications.

Publications

Unfolded Protein Response Suppression in Yeast by Loss of tRNA Modifications.

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