Ligand induced galectin-3 protein self-association

Area of Science:

• Biochemistry
• Molecular Biology
• Glycobiology

Background:

• Galectin-3 functions involve binding glycoproteins via its carbohydrate recognition site.
• Cross-linking was previously attributed to galectin-3's N-terminal domain.
• The precise mechanisms of galectin-3 multimerization and glycoprotein interaction require further elucidation.

Purpose of the Study:

• To investigate the self-association mechanisms of galectin-3 when interacting with the model glycoprotein asialofetuin (ASF).
• To differentiate between N-terminal domain-mediated (Type-N) and carbohydrate recognition site-mediated (Type-C) self-association.
• To characterize the conditions and consequences of galectin-3 self-association, including precipitation.

Main Methods:

• Fluorescence anisotropy assays were employed to quantify free galectin-3 carbohydrate recognition sites.
• Turbidimetry and dynamic light scattering were used to measure precipitation and particle size.
• Studies utilized wild-type galectin-3, a mutant (R186S), and galectin-3 lacking N-terminal domains, alongside ASF and specific glycans.

Main Results:

• ASF induced significant galectin-3 engagement, exceeding expected binding stoichiometry, suggesting self-association.
• A novel Type-C self-association mechanism, mediated by the carbohydrate recognition site, was identified, leading to oligomer formation and precipitation.
• Type-C self-association and precipitation occurred even with a poorly ASF-binding galectin-3 mutant and N-terminally truncated galectin-3, albeit with different efficiencies.

Conclusions:

• Galectin-3 can self-associate via its carbohydrate-binding site (Type-C), distinct from N-terminal mediated (Type-N) associations.
• Type-C self-association plays a crucial role in galectin-3-glycoprotein complex formation and precipitation.
• Understanding these distinct self-association modes provides new insights into galectin-3's diverse biological functions.