Abstract
Nα-terminal acetylation (NTA) is a prevalent protein modification in eukaryotes. In plants, the biological function of NTA remains enigmatic. The dominant N-acetyltransferase (Nat) in Arabidopsis (Arabidopsis thaliana) is NatA, which cotranslationally catalyzes acetylation of ∼40% of the proteome. The core NatA complex consists of the catalytic subunit NAA10 and the ribosome-anchoring subunit NAA15. In human (Homo sapiens), fruit fly (Drosophila melanogaster), and yeast (Saccharomyces cerevisiae), this core NatA complex interacts with NAA50 to form the NatE complex. While in metazoa, NAA50 has N-acetyltransferase activity, yeast NAA50 is catalytically inactive and positions NatA at the ribosome tunnel exit. Here, we report the identification and characterization of Arabidopsis NAA50 (AT5G11340). Consistent with its putative function as a cotranslationally acting Nat, AtNAA50-EYFP localized to the cytosol and the endoplasmic reticulum but also to the nuclei. We demonstrate that purified AtNAA50 displays Nα-terminal acetyltransferase and lysine-ε-autoacetyltransferase activity in vitro. Global N-acetylome profiling of Escherichia coli cells expressing AtNAA50 revealed conservation of NatE substrate specificity between plants and humans. Unlike the embryo-lethal phenotype caused by the absence of AtNAA10 and AtNAA15, loss of NAA50 expression resulted in severe growth retardation and infertility in two Arabidopsis transfer DNA insertion lines (naa50-1 and naa50-2). The phenotype of naa50-2 was rescued by the expression of HsNAA50 or AtNAA50. In contrast, the inactive ScNAA50 failed to complement naa50-2 Remarkably, loss of NAA50 expression did not affect NTA of known NatA substrates and caused the accumulation of proteins involved in stress responses. Overall, our results emphasize a relevant role of AtNAA50 in plant defense and development, which is independent of the essential NatA activity.
Highlights
Nα-terminal acetylation (NTA) is a global proteome imprinting mechanism conserved in all three domains of life and affecting up to 60% of the soluble yeast proteins and80-90% of the soluble proteins in Arabidopsis thaliana and humans (Polevoda and Sherman, 2003; Falb et al, 2006; Arnesen et al, 2009a; Bienvenut et al, 2012).Despite the prevalent frequency of N-terminal acetylation marks in the proteomes of multi-cellular controversially
Down-regulation of NatA by genetic engineering resulted in constitutive activation of the abscisic acid (ABA) response and, drought-resistant plants (Linster et al, 2015). These findings suggest that NTA in plants is not static but a highly dynamic process, which responds to environmental cues and contributes to the regulation of stress responses
Our results suggest that endogenous AtNAA25 assembles with AtNAA20 or HsNAA20 to a functional NatB complex, while interaction with ScNAA20 either failed or produced a catalytically inactive complex in planta
Summary
Nα-terminal acetylation (NTA) is a global proteome imprinting mechanism conserved in all three domains of life and affecting up to 60% of the soluble yeast proteins and80-90% of the soluble proteins in Arabidopsis thaliana and humans (Polevoda and Sherman, 2003; Falb et al, 2006; Arnesen et al, 2009a; Bienvenut et al, 2012).Despite the prevalent frequency of N-terminal acetylation marks in the proteomes of multi-cellular controversially. Nα-terminal acetylation (NTA) is a global proteome imprinting mechanism conserved in all three domains of life and affecting up to 60% of the soluble yeast proteins and. 80-90% of the soluble proteins in Arabidopsis thaliana and humans (Polevoda and Sherman, 2003; Falb et al, 2006; Arnesen et al, 2009a; Bienvenut et al, 2012). Despite the prevalent frequency of N-terminal acetylation marks in the proteomes of multi-cellular controversially. NTA is catalyzed by N-terminal acetyltransferase (Nat) complexes consisting of at least one catalytic and facultative auxiliary subunits. The auxiliary subunits are in some cases required for catalytic activity and anchor the catalytic subunit to the ribosome (Aksnes et al, 2015a; Aksnes et al, 2019). Since all five yeast Nat complexes, NatA-E, are ribosome-associated and no deacetylases acting on the N-
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