Genome-wide analysis of SPAK/OSR1 binding motifs

Based on the alignment of 12 sequences of protein motifs that interact with the kinases SPAK (Ste20-related proline alanine-rich kinase) and OSR1 (oxidative stress response 1), we performed genome-wide searches of the sequence [S/G/V]RFx[V/I]xx[V/I/T/S]xx, where x represents any amino acid. The "Mus musculus" search resulted in the identification of 131 mouse proteins containing 137 SPAK/OSR1 putative binding motifs. Similar numbers were found for human, zebrafish, fruit fly, and worm. A little more than half of the mouse proteins containing SPAK/OSR1 binding domains (53%) were also identified in the human search, whereas approximately 17-18% of these common hits were identified in the zebrafish search. The mouse proteins could be divided into two broad categories: 2/3 had an identified function, whereas 1/3 were either predicted or of unknown function. The known proteins were grouped as transport proteins, other membrane proteins, kinases, phosphatases, cytoskeletal, ribosomal, nuclear, enzymes, and others. Analysis of the location of the SPAK/OSR1 binding motif within the protein sequence revealed distribution throughout the entire length, but with preference to the extreme amino- or carboxyl termini for a large number of proteins. Analysis of the amino acid composition of the motifs revealed a preponderance of serine residues at positions 5, 6, 7, and 8. In summary, our new search found and thus confirms the 12 proteins previously shown to interact with the kinases and identifies 119 potential new targets for SPAK and OSR1 in the mouse proteome.