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 diverse stimuli. Maintaining specificity in signaling through MAPK networks is key to coupling distinct inputs to appropriate cellular responses. Docking sites-short linear motifs found in MAPK substrates, regulators, and scaf-folds-can promote signaling specificity through selective interactions, but how they do so remains unresolved. Here, we screened a proteomic library for sequences interacting with the MAPKs extracellular signal- regulated kinase 2 (ERK2) and p38 alpha, identifying selective and promiscuous docking motifs. Sequences specific for p38 alpha had high net charge and lysine content, and selective binding depended on a pair of acidic residues unique to the p38 alpha docking interface. Finally, we validated a set of full- length proteins harboring docking sites selected in our screens to be authentic MAPK interactors and substrates. This study identifies features that help define MAPK signaling networks and explains how specific docking motifs promote signaling integrity.