Rewiring of RSK–PDZ Interactome by Linear Motif Phosphorylation

Phosphorylation of short linear peptide motifs is a widespread process for the dynamic regulation of protein–protein interactions. However, the global impact of phosphorylation events on the protein–protein interactome is rarely addressed. The disordered C-terminal tail of ribosomal S6 kinase 1 (RSK1) binds to PDZ domain-containing scaffold proteins, and it harbors a phosphorylatable PDZ-binding motif (PBM) responsive to epidermal growth factor stimulation. Here, we examined binding of two versions of the RSK1 PBM, either phosphorylated or unphosphorylated at position −3, to almost all (95%) of the 266 PDZ domains of the human proteome. PBM phosphorylation dramatically altered the PDZ domain-binding landscape of RSK1, by strengthening or weakening numerous interactions to various degrees. The RSK–PDZome interactome analyzed in this study reveals how linear motif-based phospho-switches convey stimulus-dependent changes in the context of related network components.