Identification and Analysis of the Acetylated Status of Poplar Proteins Reveals Analogous N-Terminal Protein Processing Mechanisms with Other Eukaryotes

Background: The N-terminal protein processing mechanism (NPM) including N-terminal Met excision (NME) and N-terminal acetylation (N-alpha-acetylation) represents a common protein co-translational process of some eukaryotes. However, this NPM occurred in woody plants yet remains unknown. Methodology/Principal Findings: To reveal the NPM in poplar, we investigated the N-alpha-acetylation status of poplar proteins during dormancy by combining tandem mass spectrometry with TiO2 enrichment of acetylated peptides. We identified 58 N-terminally acetylated (N-alpha-acetylated) proteins. Most proteins (47, >81%) are subjected to N-alpha-acetylation following the N-terminal removal of Met, indicating that N-alpha-acetylation and NME represent a common NPM of poplar proteins. Furthermore, we confirm that poplar shares the analogous NME and N-alpha-acetylation (NPM) to other eukaryotes according to analysis of N-terminal features of these acetylated proteins combined with genome-wide identification of the involving methionine aminopeptidases (MAPs) and N-terminal acetyltransferase (Nat) enzymes in poplar. The N-alpha-acetylated reactions and the involving enzymes of these poplar proteins are also identified based on those of yeast and human, as well as the subcellular location information of these poplar proteins. Conclusions/Significance: This study represents the first extensive investigation of N-alpha-acetylation events in woody plants, the results of which will provide useful resources for future unraveling the regulatory mechanisms of N-alpha-acetylation of proteins in poplar.