Correlated Segments of Intrinsically Disordered Proteins as Drivers of Homotypic Phase Separation

Many studies have suggested that amino acid composition, not their positions along the sequence, is the determinant of phase separation of intrinsically disordered proteins (IDPs). In particular, aromatic amino acids and Arg have been identified as major drivers. Here I underscore the importance of the positions of amino acids along the sequence in phase separation. Specifically, clusters of interaction-prone amino acids, including Trp and Arg, along the sequence form correlated segments, and these correlated segments, rather than individual residues, drive the phase separation of many IDPs. Correlated segments manifest themselves as stretches of residues that span major peaks in the backbone 15N NMR transverse relaxation rates and can be predicted by a sequence-based method called SeqDYN (https://zhougroup-uic.github.io/SeqDYNidp/). Inter-chain interactions between individual residues may be too transient, but those between correlated segments involve multiple residues can provide the strengths required for phase separation. Indeed, sequence motifs revealed by NMR and other techniques as important for phase separation frequently map to SeqDYN-predicted correlated segments. These include residues G624-R626, G638-R640, and R660-Q666 of CAPRIN1, residues R21-G30 of LAF-1, and residues Q9-P21 of FUS. SeqDYN presents a sequence-based method for identifying motifs that drive phase separation of IDPs.