Ligand induced galectin-3 self-association.

Summary, in English

Many functions of galectin-3 entail binding of its carbohydrate recognition site to glycans of a glycoprotein, resulting in cross-linking thought to be mediated by its N-terminal non-carbohydrate-binding domain. Here we studied interaction of galectin-3 with the model glycoprotein asialofetuin (ASF), using a fluorescence anisotropy (FA) assay to measure the concentration of free galectin carbohydrate recognition sites in solution. Surprisingly, in the presence of ASF this remained low even at high galectin-3 concentrations, showing that many more galectin-3 molecules were engaged than expected due to the about 9 known glycan based binding sites per ASF molecule. This suggests that, after ASF induced nucleation, galectin-3 associates with itself by the carbohydrate recognition site binding to another galectin-3 molecule, possibly forming oligomers. We named this type-C self-association to distinguish it from the previously proposed models (type-N) where galectin-3 molecules bind to each other through the N-terminal domain, and all carbohydrate recognition sites are available for binding glycans. Both types of self-association can result in precipitates, as measured here by turbidometry and dynamic light scattering. Type-C self-association and precipitation occurred even with a galectin-3 mutant (R186S) that bound poorly to ASF, but required much higher concentration (~50μM) compared to wild type (~1μM). ASF also induced weaker type-C self-association of galectin-3 lacking its N-terminal part, but, as expected, no precipitation. Neither a monovalent or divalent LacNAc containing glycan induced type-C self-association, even if the latter gave precipitates with high concentrations of galectin-3 (> ~50μM) in agreement with published results, and perhaps due to type-N self-association.

• Author: Adriana Lepur; Emma Salomonsson; Ulf J Nilsson; Hakon Leffler
• Department/s: BioCARE: Biomarkers in Cancer Medicine improving Health Care, Education and Innovation; Division of Microbiology, Immunology and Glycobiology - MIG; Centre for Analysis and Synthesis
• Publishing year: 2012
• Language: English
• Pages: 21751-21756
• Publication/Series: Journal of Biological Chemistry
• Volume: 287
• Issue: 26
• Links: http://dx.doi.org/10.1074/jbc.C112.358002
• Document type: Journal article
• Publisher: American Society for Biochemistry and Molecular Biology
• Topic: Microbiology in the medical area; Immunology in the medical area
• Status: Published
• ISBN/ISSN/Other: ISSN: 1083-351X