Protein Language: Post-Translational Modifications Talking to Each Other

Recent studies highlight the importance of crosstalk between different PTMs in several plant signaling pathways. Combinatory PTM codes are the result of distinct molecular mechanisms, leading to different outcomes, although mainly to ensure a tight regulation in response to environmental changes. By its abundance, protein phosphorylation has a central role in protein crosstalk, but emerging studies on ubiquitination and sumoylation also highlight roles for these modifications in plant protein crosstalk. Advances in mass spectrometry allow the identification of PTM crosstalk, enabling a more precise understanding of plant signaling processes. Post-translational modifications (PTMs) are at the heart of many cellular signaling events. Apart from a single regulatory PTM, there are also PTMs that function in orchestrated manners. Such PTM crosstalk usually serves as a fine-tuning mechanism to adjust cellular responses to the slightest changes in the environment. While PTM crosstalk has been studied in depth in various species; in plants, this field is just emerging. In this review, we discuss recent studies on crosstalk between three of the most common protein PTMs in plant cells, being phosphorylation, ubiquitination, and sumoylation, and we highlight the diverse underlying mechanisms as well as signaling outputs of such crosstalk. Post-translational modifications (PTMs) are at the heart of many cellular signaling events. Apart from a single regulatory PTM, there are also PTMs that function in orchestrated manners. Such PTM crosstalk usually serves as a fine-tuning mechanism to adjust cellular responses to the slightest changes in the environment. While PTM crosstalk has been studied in depth in various species; in plants, this field is just emerging. In this review, we discuss recent studies on crosstalk between three of the most common protein PTMs in plant cells, being phosphorylation, ubiquitination, and sumoylation, and we highlight the diverse underlying mechanisms as well as signaling outputs of such crosstalk. self-modification of a modifying enzyme can occur either independently of the oligomerization status of the protein, where the protein can modify itself (in cis), or in an oligomer, where each protomer can modify another protomer (in trans). ubiquitin/SUMO is activated by an ATP-dependent formation of a thioester bond between a catalytic cysteine on the E1 ligase and the ubiquitin/SUMO protein, which is transferred to an E2 ligase via trans-thioesterification. Finally, the E2 ligase catalyzes the conjugation of ubiquitin/SUMO to the substrate via complex formation with the substrate and the E3 ligase core [44Saracco S.A. et al.Genetic analysis of SUMOylation in Arabidopsis: conjugation of SUMO1 and SUMO2 to nuclear proteins is essential.Plant Physiol. 2007; 145: 119-134Crossref PubMed Scopus (218) Google Scholar, 78Wang F. Deng X.W. Plant ubiquitin-proteasome pathway and its role in gibberellin signaling.Cell Res. 2011; 21: 1286-1294Crossref PubMed Scopus (79) Google Scholar]. E1-E2-E3-protein conjugation cascades commonly form complex polyubiquitin or polySUMO chains. While both SUMO and ubiquitin have various similar nonproteolytic functions in cells, in contrast to ubiquitin, no proteasomal machineries have been yet shown to use the polySUMO chain directly as a marker for degradation [60Perry J.J.P. et al.A SIM-ultaneous role for SUMO and ubiquitin.Trends Biochem. 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