The return of the rings: Evolutionary convergence of aromatic residues in the intrinsically disordered regions of RNA-binding proteins for liquid-liquid phase separation

Aromatic residues appeared relatively late in the evolution of protein sequences to stabilize the globular proteins' folding core and are less in the intrinsically disordered regions (IDRs). Recent advances in protein liquid-liquid phase separation (LLPS) studies have also shown that aromatic residues in IDRs often act as stickers to promote multivalent interactions in forming higher-order oligomers. To study how general these structure-promoting residues are in IDRs, we compared levels of sequence disorder in RNA binding proteins (RBPs), which are often found to undergo LLPS, and the human proteome. We found that aromatic residues appear more frequently than expected in the IDRs of RBPs and, through multiple sequence alignment analysis, those aromatic residues are often conserved among chordates. Using TDP-43, FUS, and some other well-studied LLPS proteins as examples, the conserved aromatic residues are important to their LLPS-related functions. These analyses suggest that aromatic residues may have contributed twice to evolution: stabilizing structured proteins and assembling biomolecular condensates.

Automated summary

Aromatic residues are frequently found in the intrinsically disordered regions (IDRs) of RNA binding proteins (RBPs) and are often conserved among chordates. These residues play a crucial role in protein liquid-liquid phase separation (LLPS) and contribute to the formation of higher-order oligomers. This suggests that aromatic residues have played a significant role in the evolution of protein folding and biomolecular condensate assembly.