Kinase interaction analysis predicts actions of the WNK-OSR1/SPAK pathway

The WNK-OSR1/SPAK protein kinase pathway regulates ion homeostasis and cell volume, but its other functions are not well understood. To discover undefined signaling functions, we utilized experimentally-derived binding specificity to predict interactions and relative affinities with the conserved C-terminal (CCT) domains of OSR1 and SPAK, which bind short linear motifs. The upstream kinases WNKs 1-4 and their relatives, the pseudokinases NRBP1/2, also contain CCT-like domains which have conserved folds and motif binding pockets. Motifs were scored using peptide arrays, conservation, cytosolic localization, and solvent accessibility. Out of nearly 3700 motifs in the human proteome, 90% of previously published motifs ranked in the top 2% of those predicted. Interactions with selected candidates, including TSC22D1 and CAVIN1, were validated, and their localization and/or modifications were coupled to changes in WNK1 signaling. We also identified additional motif variants and confirmed binding to the NRBP1 CCT-like domain. Our results stress the diverse functionality of CCT/CCT-like domains and implicates unexpected interactions driving WNK biology.