Abstract
Galectins represent β-galactoside-binding proteins with numerous functions. Due to their role in tumor progression, human galectins-1, -3 and -7 (Gal-1, -3 and -7) are potential targets for cancer therapy. As plant derived glycans might act as galectin inhibitors, we prepared galactans by partial degradation of plant arabinogalactan-proteins. Besides commercially purchased galectins, we produced Gal-1 and -7 in a cell free system and tested binding capacities of the galectins to the galactans by biolayer-interferometry. Results for commercial and cell-free expressed galectins were comparable confirming functionality of the cell-free produced galectins. Our results revealed that galactans from Echinacea purpurea bind to Gal-1 and -7 with KD values of 1–2 µM and to Gal-3 slightly stronger with KD values between 0.36 and 0.70 µM depending on the sensor type. Galactans from the seagrass Zostera marina with higher branching of the galactan and higher content of uronic acids showed stronger binding to Gal-3 (0.08–0.28 µM) compared to galactan from Echinacea. The results contribute to knowledge on interactions between plant polysaccharides and galectins. Arabinogalactan-proteins have been identified as a new source for production of galactans with possible capability to act as galectin inhibitors.
Highlights
Galectins are a family of evolutionarily conserved glycan-binding proteins present in organisms from nematodes to mammals, which are characterized by their affinity for β-galactosides
Galectins do not have a signal sequence, which would be required for protein secretion through the classical secretory pathway, they can be secreted by a non-classical mechanism that bypasses the Golgi apparatus [2]
Alkaline treatment leads to destruction of the protein moiety, whereas mild acid hydrolysis causes cleavage of labile monosaccharide linkage types
Summary
Galectins are a family of evolutionarily conserved glycan-binding proteins present in organisms from nematodes to mammals, which are characterized by their affinity for β-galactosides. The latter residues are present intracellularly, in the extracellular matrix or as part of cell surface glycoconjugates [1]. Gal-3 is the only mammalian representative of the second subfamily, the chimeric galectins, which have a single C-terminal CRD and a large N-terminus of about 120–160 amino acids. The tandem-repeat galectins (Gal-4, -8, -9, -12) have two different CRDs connected by a flexible peptide linker of 5 to more than 50 amino acids
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