NAA50 Is an Enzymatically Active N^α-Acetyltransferase That Is Crucial for Development and Regulation of Stress Responses

Abstract

N a-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 N a-terminal acetyltransferase and lysine-«-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.

The versatile interactome of chloroplast ribosomes revealed by affinity purification mass spectrometry

“…Furthermore, the abundance of the cytosolic ribosome-associated NatA complex is tightly regulated by the drought stress-related hormone ABA ( 83 ). NTA of cytosolic proteins by the ribosome-associated complexes NatA, NatB and NatE is also essential for the responses to pathogen-attack or high salt stress ( 84 , 85 ). Based on these results, co-translational and post-translational NTA is supposed to affect diverse stress responses in plants ( 86 ).…”

Dual lysine and N‐terminal acetyltransferases reveal the complexity underpinning protein acetylation

“…The consensual knowledge favors distinct enzymes for the acetylation of protein N‐termini and lysine residues (Liszczak et al , ; Magin et al , ). The cytosolic acetyltransferases NAA40, NAA50, and NAA60 have been shown to display weak KA and strong NTA activities (Evjenth et al , ; Liu et al , ; Chu et al , ; Yang et al , ; Stove et al , ; Armbruster et al , ; Linster et al , ). However, there still is controversy on whether or not NAA10 might catalyze both reactions (Friedmann & Marmorstein, ; Magin et al , ).…”

The Arabidopsis Nα‐acetyltransferase NAA60 locates to the plasma membrane and is vital for the high salt stress response

“…The NatA complex can also associate with the auxiliary subunit HypK and an additional catalytic subunit NAA50. In the latter case, the complex of NatA and NAA50 is termed NatE (Gautschi et al ., 2003; Weyer et al ., 2017; Gottlieb & Marmorstein, 2018; Deng et al ., 2019; Armbruster et al ., 2020). In higher eukaryotes, post‐translational Nats (NatF–NatH) have been identified (Aksnes et al ., 2015b; Dinh et al ., 2015; Drazic et al ., 2018).…”