Enhanced access to the human phosphoproteome with genetically encoded phosphothreonine.

Protein phosphorylation is a ubiquitous post-translational modification used to regulate cellular processes and proteome architecture by modulating protein-protein interactions. The identification of phosphorylation events through proteomic surveillance has dramatically outpaced our capacity for functional assignment using traditional strategies, which often require knowledge of the upstream kinase a priori. The development of phospho-amino-acid-specific orthogonal translation systems, evolutionarily divergent aminoacyl-tRNA synthetase and tRNA pairs that enable co-translational insertion of a phospho-amino acids, has rapidly improved our ability to assess the physiological function of phosphorylation by providing kinase-independent methods of phosphoprotein production. Despite this utility, broad deployment has been hindered by technical limitations and an inability to reconstruct complex phopho-regulatory networks. Here, we address these challenges by optimizing genetically encoded phosphothreonine translation to characterize phospho-dependent kinase activation mechanisms and, subsequently, develop a multi-level protein interaction platform to directly assess the overlap of kinase and phospho-binding protein substrate networks with phosphosite-level resolution.