Phosphoproteomic Analysis of Spiroplasma eriocheiris and Crosstalk with Acetylome Reveals the Role of Post-Translational Modifications in Metabolism

Background: Post-Translational Modifications (PTMs), such as phosphorylation, are an essential regulatory mechanism of protein function and are associated with a range of biological processes beyond the genome and transcriptome. Spiroplasma eriocheiris, a wall-less helical bacterium, is one of the smallest self-replicating bacteria, and is a novel pathogen of freshwater crustaceans. Methods: Protein phosphorylation in S. eriocheiris was systematically investigated by iTRAQ analyzed by LC-MS/MS to study the physiological characteristics and regulatory mechanisms of this bacteria. Data are available via ProteomeXchange with identifier PXD015055. Results: We identified 465 phosphorylation sites in 246 proteins involved in a broad spectrum of fundamental biological processes ranging from the regulation of metabolic pathways to protein synthesis. Notably, most proteins involved in glycolysis and all proteins in the arginine deiminase system were phosphorylated. Cytoskeleton proteins (Fibril, Mrebs and EF-Tu) were also phosphorylated suggesting that phosphorylation may play a crucial role in the formation of the cell skeleton. The analysis identified a number of highly conserved proteins and phosphorylation sites that predominantly participate in glucose metabolism and protein synthesis. Crosstalk analysis with protein-protein interaction networks in relation to phosphorylated proteins and acetylated proteins found that the two PTMs are involved in a number of crucial physiological processes in S. eriocheiris. Comparison of the relative positions of acetylation versus phosphorylation revealed that the two modifications are often located in close proximity to the same protein. Conclusion: The results indicate a previously unreported role of phosphorylation in defining the functional state of Spiroplasma.