Proteome-Wide Discovery of Evolutionary Conserved Sequences in Disordered Regions

A statistical analysis method can identify short, functionally important linear motifs in disordered regions of proteins. Finding the Hidden Meaning in Disordered Regions Many proteins, including those involved in signal transduction, have large disordered regions, in addition to their clearly defined domains or motifs. Although these disordered regions are functionally important, identifying the important residues in these regions has proved challenging because the regions are not visualized in crystal structures and tend to exhibit high sequence divergence. Nguyen Ba et al. modified the phylogenetic hidden Markov model so that it could be applied to these disordered regions. Application of this method to yeast proteins not only revealed the presence of known short conserved motifs in proteins not known to have these motifs but also predicted previously unknown short conserved motifs. Experimental analysis suggested that both sets of motifs were functionally important. Thus, this approach should provide an effective method for discovering biologically important conserved motifs within the disordered regions of proteins. At least 30% of human proteins are thought to contain intrinsically disordered regions, which lack stable structural conformation. Despite lacking enzymatic functions and having few protein domains, disordered regions are functionally important for protein regulation and contain short linear motifs (short peptide sequences involved in protein-protein interactions), but in most disordered regions, the functional amino acid residues remain unknown. We searched for evolutionarily conserved sequences within disordered regions according to the hypothesis that conservation would indicate functional residues. Using a phylogenetic hidden Markov model (phylo-HMM), we made accurate, specific predictions of functional elements in disordered regions even when these elements are only two or three amino acids long. Among the conserved sequences that we identified were previously known and newly identified short linear motifs, and we experimentally verified key examples, including a motif that may mediate interaction between protein kinase Cbk1 and its substrates. We also observed that hub proteins, which interact with many partners in a protein interaction network, are highly enriched in these conserved sequences. Our analysis enabled the systematic identification of the functional residues in disordered regions and suggested that at least 5% of amino acids in disordered regions are important for function.