Dataset Information

Global and protein-specific analysis reveals Nt-acetylation-independent turnover of SQE1 by Arabidopsis DOA10-like E3 ligases

ABSTRACT: The Acetylation-dependent (Ac/) N-degron pathway degrades proteins through recognition of their acetylated N-termini (Nt) by specific E3-ligases (Ac/N-recognins). To date, no Ac/N-recognins have been defined in plants. Here we use molecular, genetic, and multi-omics approaches to characterise potential roles for Arabidopsis DOA10-like E3-ligases in the Nt-acetylation-(NTA-) dependent turnover of proteins at global and protein-specific scales. Arabidopsis has two ER-localised DOA10-like proteins. AtDOA10A, but not the Brassicaceae-specific AtDOA10B, can compensate for loss of yeast ScDOA10 function. Transcriptome and Nt-acetylome profiling of an Atdoa10a/b RNAi mutant revealed no significant differences in the global NTA profile compared to wildtype, suggesting that AtDOA10s do not regulate the bulk turnover of NTA substrates. Using protein steady-state and cycloheximide-chase degradation assays in yeast and Arabidopsis, we show that turnover of ER-localised squalene epoxidase 1 (AtSQE1), a critical sterol biosynthesis enzyme, is mediated by AtDOA10s. Degradation of AtSQE1 in planta does not depend on NTA, but Nt-acetyltransferases indirectly impact its turnover in yeast, indicating kingdom-specific differences in NTA and cellular proteostasis. Our work suggests that, in contrast to yeast and mammals, targeting of Nt-acetylated proteins is not a major function of DOA10-like E3 ligases in Arabidopsis, and provides further insight into plant ERAD and the conservation of regulatory mechanisms controlling sterol biosynthesis in eukaryotes.

INSTRUMENT(S): LTQ Orbitrap Velos

ORGANISM(S): Arabidopsis Thaliana (mouse-ear Cress)

TISSUE(S): Rosette

SUBMITTER: Jean Baptiste BOYER

LAB HEAD: Carmela GIGLIONE

PROVIDER: PXD043217 | Pride | 2024-01-26

REPOSITORIES: Pride

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Publications

Nt-acetylation-independent turnover of SQUALENE EPOXIDASE 1 by Arabidopsis DOA10-like E3 ligases.

Etherington Ross D RD Bailey Mark M Boyer Jean-Baptiste JB Armbruster Laura L Cao Xulyu X Coates Juliet C JC Meinnel Thierry T Wirtz Markus M Giglione Carmela C Gibbs Daniel J DJ

Plant physiology 20231001 3

The acetylation-dependent (Ac/)N-degron pathway degrades proteins through recognition of their acetylated N-termini (Nt) by E3 ligases called Ac/N-recognins. To date, specific Ac/N-recognins have not been defined in plants. Here we used molecular, genetic, and multiomics approaches to characterize potential roles for Arabidopsis (Arabidopsis thaliana) DEGRADATION OF ALPHA2 10 (DOA10)-like E3 ligases in the Nt-acetylation-(NTA)-dependent turnover of proteins at global- and protein-specific scales ...[more]

PMID: 37427787

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Project description:Co-translational N-terminal (Nt-) acetylation of nascent polypeptides is catalyzed by N-terminal acetyltransferases (NATs). The very N-terminal amino acid sequence is the major factor determining whether or not a given protein is Nt-acetylated. In humans, six different NATs, denoted NatA-NatF, are identified. In the current study we used N-terminal COFRADIC analysis to define the in vivo substrate specificity of Naa50 (Nat5)/NatE as this has long remained elusive. Three yeast strains were generated; a control strain endogenously expressing yNaa50, a deletion strain depleted of yNaa50 and a strain deleted of yNaa50 but ectopically expressing human Naa50. When comparing the Nt-acetylation status of different N-termini in the control strain with the deletion strain, a reduction in Nt-acetylation for several yeast proteins was observed. To our surprise, these substrates were not of the predicted NatE-type substrates, but rather canonical NatA substrates. Further, ectopic expression of hNaa50 mainly resulted in the Nt-acetylation of a selected class of otherwise Nt-free yeast N-termini besides increasing the degree of Nt-acetylation of several other yeast proteins, and as such (partially) complementing those N-termini displaying reduced Nt-acetylation upon yNAA50-deletion. The preferred substrates of hNaa50 were predominantly Met-starting N-termini including Met-Lys-, Met-Val-, Met-Ala-, Met-Tyr-, Met-Phe-, Met-Leu-, Met-Ser- and Met-Thr, and highly overlapped with the previously identified human Naa60/NatF substrate specificity profile. Identification of several hNaa50 substrates with a small amino acid in the second position also revealed a potential interplay between the NATs and methionine aminopeptidases (MetAPs). The initiator Methionine (iMet) is normally cleaved off by MetAPs when the second amino acid is small, but our in vitro data suggest that in contrast to a free iMet, an Nt-acetylated iMet is not hydrolyzed by MetAPs. Thus, Naa50-mediated Nt-acetylation may potentially act as a mechanism to retain the iMet of proteins with a small amino acid at the second position that normally would be hydrolyzed.

Project description:In Arabidopsis thaliana the evolutionary conserved N-terminal acetyltransferase (Nat) complexes NatA and NatB co-translationally acetylate 60% of the proteome. Both have recently been implicated in the regulation of plant stress responses. While NatA mediates drought tolerance, NatB is required for pathogen resistance and the adaptation to high salinity and high osmolarity. Salt and osmotic stress impair protein folding and result in the accumulation of misfolded proteins in the endoplasmic reticulum (ER). The ER-membrane resident E3 ubiquitin ligase DOA10 targets misfolded proteins for degradation during ER stress and is conserved among eukaryotes. In yeast, DOA10 recognizes conditional degradation signals (Ac/N-degrons) created by NatA and NatB. Assuming that this mechanism is preserved in plants, the lack of Ac/N-degrons required for efficient removal of misfolded proteins might explain the sensitivity of NatB mutants to protein harming conditions. In this study, we investigate the response of NatB mutants to dithiothreitol (DTT) and tunicamycin (TM) induced ER stress. We report that NatB mutants are hypersensitive to DTT but not TM, suggesting that the DTT hypersensitivity is caused by an over-reduction of the cytosol rather than an accumulation of unfolded proteins in the ER. In line with this hypothesis, the cytosol of NatB depleted plants is constitutively over-reduced and a global transcriptome analysis reveals that their reductive stress response is permanently activated. Moreover, we demonstrate that doa10 mutants are susceptible to neither DTT nor TM, ruling out a substantial role of DOA10 in ER-associated protein degradation (ERAD) in plants. Contrary to previous findings in yeast, our data indicates that N-terminal acetylation (NTA) does not inhibit ER targeting of a substantial amount of proteins in plants. In summary, we provide further evidence that NatB-mediated imprinting of the proteome is vital for the response to protein-harming stress and rule out DOA10 as the sole recognin for substrates in the plant ERAD pathway.

Dataset Information

Global and protein-specific analysis reveals Nt-acetylation-independent turnover of SQE1 by Arabidopsis DOA10-like E3 ligases

Publications

Nt-acetylation-independent turnover of SQUALENE EPOXIDASE 1 by Arabidopsis DOA10-like E3 ligases.

Similar Datasets

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