Liquid-liquid phase separation and extracellular multivalent interactions in the tale of galectin-3

Abstract

Liquid-liquid phase separation (LLPS) explains many intracellular activities, but its role in extracellular functions has not been studied to the same extent. Here we report how LLPS mediates the extracellular function of galectin-3, the only monomeric member of the galectin family. The mechanism through which galectin-3 agglutinates (acting as a "bridge" to aggregate glycosylated molecules) is largely unknown. Our data show that its N-terminal domain (NTD) undergoes LLPS driven by interactions between its aromatic residues (two tryptophans and 10 tyrosines). Our lipopolysaccharide (LPS) micelle model shows that the NTDs form multiple weak interactions to other galectin-3 and then aggregate LPS micelles. Aggregation is reversed when interactions between the LPS and the carbohydrate recognition domains are blocked by lactose. The proposed mechanism explains many of galectin-3's functions and suggests that the aromatic residues in the NTD are interesting drug design targets.

Relevance of Electrostatic Charges in Compactness, Aggregation, and Phase Separation of Intrinsically Disordered Proteins

“…In contrast with the three examples above, the N-terminal prion-like domain of galectin-3 undergoes LLPS only when the NaCl concentration is increased above 600 mM, with LLPS being driven by π-π interactions between aromatic residues [146].…”

Biomolecular Condensates and Cancer

“…Elastin is the best characterized ECM protein whose polymeric assembly is initiated by phase separation (Bellingham et al, 2003;Kozel et al, 2006;MacEwan and Chilkoti, 2010;Muiznieks et al, 2018;Reichheld et al, 2017;Vrhovski et al, 1997). There are additional proteins that are thought to contribute to ECM dynamics and may be involved in tumor processes; as an example, galectin-3-agglutinated glycosylated molecules in the ECM tumor stroma are thought to undergo phase separation (Chiu et al, 2020). Improved understanding of condensate components and regulation in the ECM might provide novel therapeutic avenues in cancer.…”

Liquid–Liquid Phase Separation by Intrinsically Disordered Protein Regions of Viruses: Roles in Viral Life Cycle and Control of Virus–Host Interactions

“…The sequences of interest often encompass multiple short motifs such as YG/S-, FG-, RG-, GY-, KSPEA-, SY-and Q/N-rich regions, and blocks of alternating charges [143]. Interactions occur via different residue types, such as Phe and Tyr involved in π-π stacking and π-cationic interactions with Lys and Arg residues, polar and charged residues [139,142,[144][145][146]. Distribution of charged amino acids along the sequence has also been suggested to have a role in the coacervation propensity [147], with electrostatic interactions between blocks of oppositely charged residues being associated to stronger driving forces-through long-range, interchain attractions [143] and larger coacervation windows [129] than sequences with interspersed charges.…”