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Structural Basis Underlying the Binding Preference of Human Galectins-1, -3 and -7 for Galβ1-3/4GlcNAc

Hsieh TJ, et al., 10(5):e0125946, PLoS One, 2015

Galectins are a large family of β-galactoside-binding proteins, known to participate in a broad variety of biological functions including cell adhesion, cell growth regulation, and apoptosis. Previous studies suggest that human galectins play a critical role in processes linked to many types of cancers. It is vital to identify how each galectin member interacts with various glycan structures in connection with cancer progression for the development of new cancer therapeutics. All galectins are known to recognize Galβ1-3/4GlcNAc disaccharides, namely type 1 and 2 Lac-NAc (abbreviated as LN1 and LN2, respectively). Reported herein is the crystal structures of full-length human galectin-1 (hGal1), galectin-7 (hGal7), and the C-terminal carbohydrate recognition domain (CRD ) domain of galectin-3 (hGal3-CRD) in complex with LN1. Binding affinity of LN1 and LN2 to hGal1, hGal3 and hGal7 were studied by Bio-Layer Interferometry (BLI) and Fluorescence polarization (FP)-based competition assays. A Pall ForteBio Octet RED system equipped with biotinylated galectins captured Super Streptavidin Biosensor probes was used in the BLI assays. The free sites on the biosensor tips were blocked with biocytin in order to avoid non-specific binding. Galectin bound biosensor tips were then immersed in a concentration series of 3-fold diluted LN1/LN2 solutions. Dissociation constants were determined for the binding interactions. The dissociation constants obtained by BLI and FP-based competition assays demonstrated a highly consistent trend. Overall results from this structural study reveals why galectins display a binding preference for Galβ1-3/4GlcNAc disaccharides.

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