Abstract
N-terminal modifications play a major role in the fate of proteins in terms of activity, stability, or subcellular compartmentalization. Such modifications remain poorly described and badly characterized in proteomic studies, and only a few comparison studies among organisms have been made available so far. Recent advances in the field now allow the enrichment and selection of N-terminal peptides in the course of proteome-wide mass spectrometry analyses. These targeted approaches unravel as a result the extent and nature of the protein N-terminal modifications. Here, we aimed at studying such modifications in the model plant Arabidopsis thaliana to compare these results with those obtained from a human sample analyzed in parallel. We applied large scale analysis to compile robust conclusions on both data sets. Our data show strong convergence of the characterized modifications especially for protein N-terminal methionine excision, co-translational N-α-acetylation, or N-myristoylation between animal and plant kingdoms. Because of the convergence of both the substrates and the N-α-acetylation machinery, it was possible to identify the N-acetyltransferases involved in such modifications for a small number of model plants. Finally, a high proportion of nuclear-encoded chloroplast proteins feature post-translational N-α-acetylation of the mature protein after removal of the transit peptide. Unlike animals, plants feature in a dedicated pathway for post-translational acetylation of organelle-targeted proteins. The corresponding machinery is yet to be discovered.
Highlights
As noted as far back as 25 years ago [1,2,3], protein N-␣acetylation (NAA)1 is one of the major protein modifications of
Our simplified approach using strong cation exchange-liquid chromatography (SCX-LC) and targeting blocked N-terminal peptides of both Arabidopsis and human samples highlights the presence of a large number of NAAed proteins in both species proving the conservation of this mechanism in plants
NAA has been investigated in few studies before (6 –9, 11, 79), but this is the first report highlighting the characterization of so many proteins for A. thaliana carrying this modification
Summary
As noted as far back as 25 years ago [1,2,3], protein N-␣acetylation (NAA) is one of the major protein modifications of. NAA, a co-translational modification occurring in close vicinity of the ribosome [12,13,14], consists of the transfer of an acetyl group from the acetyl coenzyme-A to the free N-terminal group of the nascent polypeptide This reaction is catalyzed by several—at least six identified so far [15, 16]—N-␣-acetyltransferase complexes (Nats). Several recent large scale analyses of N-␣-acetylated (NAAed) proteins have been performed in Saccharomyces cerevisiae [11, 20], Homo sapiens [7, 11, 18], Drosophila melanogaster [6], Halobacterium salinarum, and Natronomonas pharaonis [8, 9] These studies have started to uncover this modification at the proteome scale leading to a better overview of the process. The associated NatC gene knock-out is specific to plants because it is associated to a chloroplast defect featured by decreasing effective quantum yield of photosystem II and, as a result, impairing plant growth [44]
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