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Linear motif specificity in signaling through p38α and ERK2 mitogen-activated protein kinases

Mitogen-activated protein kinase (MAPK) cascades are essential for eukaryotic cells to integrate and respond to a wide array of stimuli. Maintaining specificity in signaling through MAPK networks is key to coupling specific inputs to appropriate cellular responses. One way that MAPKs achieve specificity is through transient interactions with docking sites: short linear motifs found in MAPK substrates, regulators, and scaffolds. Docking sites bind to a conserved groove located in the catalytic domain of all MAPKs including the ERK and p38 subfamilies, but how specificity is achieved remains unresolved. To understand the basis of docking selectivity for these two subfamilies, we screened a library of thousands of human proteome-derived sequences for docking to ERK2 and p38α. We discovered a large number of sequences that bound specifically to only one MAPK or promiscuously to both, and that selective and non-selective interactors conformed to distinct sequence motifs. In particular, selective binding to p38α correlated with higher net charge in the docking site, and this phenomenon was driven by enrichment for Lys residues. A pair of acidic residues unique to the docking groove of p38α mediated selectivity for Lys-rich basic motifs. Finally, we validated a set of full-length proteins harboring docking sites selected as hits in our screens to be authentic MAPK interactors and identified ChREBP and TACC1 as cellular MAPK substrates. This study identifies distinguishing features that help define MAPK signaling networks and explains how specific docking motifs promote signaling integrity.