# Evolution of intrinsically disordered regions in vertebrate galectins for phase separation

## TL;DR

This paper shows how disordered regions in galectin proteins evolved to perform similar functions in different vertebrates through repeated motifs rather than specific amino acid types.

## Contribution

The study reveals that vertebrate galectin IDRs evolved functional phase separation via motif repetition, not residue specificity.

## Key findings

- Vertebrate galectin IDRs converged on phase separation despite differing aromatic residue types.
- Agglutination depends on repeated aromatic motifs, not specific residue types.
- A conserved N-terminal motif promotes self-association and likely initiated IDR expansion.

## Abstract

Intrinsically disordered regions (IDRs) are widespread in proteins, yet their evolutionary paths remain poorly understood. Using galectin, a universal carbohydrate-binding protein, we investigated how IDRs evolved and acquired their biological roles in vertebrates. Through extensive proteome-wide sequence analyses, we found that vertebrate galectin IDRs share overall amino acid compositions but differ significantly in their aromatic residue types. Using nuclear magnetic resonance (NMR) spectroscopy and lipopolysaccharide micelle assays, we demonstrated that despite these differences, IDRs from various vertebrate galectins independently converged toward a similar function: mediating agglutination via phase separation. Our data suggest that the specific types of aromatic residues within these IDRs were established early in evolution and underwent independent expansions among different vertebrate lineages. Additionally, we identified a conserved short N-terminal motif critical for promoting galectin self-association, which likely served as an incipient sequence for subsequent IDR evolution. Contrary to previous peptide studies emphasizing aromatic residue specificity, our findings highlight the evolutionary preference for increasing motif repetition over residue-type optimization to achieve functional fitness.

Vertebrate galectin IDRs evolved to drive phase separation not by selecting specific aromatic residue types, but by amplifying motif repeats. A conserved N-terminal fragment likely seeded this expansion, enabling diverse lineages to converge on similar agglutination functions.

Vertebrate galectin intrinsically disordered regions converged on phase separation functions despite diverse aromatic residue compositions.Agglutination capacity depends primarily on the quantity of repeated aromatic motifs rather than the specific aromatic residue type.A conserved N-terminal motif promotes self-association and likely served as the evolutionary seed for disordered region expansion.

Vertebrate galectin intrinsically disordered regions converged on phase separation functions despite diverse aromatic residue compositions.

Agglutination capacity depends primarily on the quantity of repeated aromatic motifs rather than the specific aromatic residue type.

A conserved N-terminal motif promotes self-association and likely served as the evolutionary seed for disordered region expansion.

Vertebrate galectin IDRs evolved to drive phase separation not by selecting specific aromatic residue types, but by amplifying motif repeats. A conserved N-terminal fragment likely seeded this expansion, enabling diverse lineages to converge on similar agglutination functions.