Targeted Profiling of Arabidopsis thaliana Subproteomes Illuminates Co- and Posttranslationally N-Terminal Myristoylated Proteins.

N-terminal myristoylation (MYR) is a biologically important co-translational protein lipidation. MYR is difficult to detect in vivo and challenging to predict in silico. We developed a targeted proteomics strategy to identify the Arabidopsis thaliana myristoylated (MYRed) proteome in specific sub-cellular compartments. This global profiling approach allowed us to: (i) identify one third of all open reading frames of the A. thaliana proteome including 54% of the predicted myristoylome; and (ii) establish the first comprehensive plant myristoylome, featuring direct evidence of MYR in 72 proteins. Eighteen MYRed proteins were unexpected, indicating that the in vivo A. thaliana myristoylome extends beyond current predicted sets. A MYR site was also identified downstream of a predicted initiation codon, indicating that post-translational MYR occurs in plants. Over half of the identified proteins could be quantified and assigned to a subcellular compartment. Hierarchical clustering of protein accumulation profiles combined with MYR data and the S-acylated (PALed) proteome revealed that N-terminal double acylation drastically influences protein redirection to the plasma membrane. In a few cases, MYR function extended beyond simple membrane association. This study identified hundreds of N-acylated proteins for which these modifications have the potential to define new protein localization control mechanisms and expand protein function.