Galectin-10: a new structural type of prototype galectin dimer and effects on saccharide ligand binding

Abstract

Galectin-10 (Gal-10) which forms Charcot-Leyden crystals in vivo, is crucial to regulating lymph cell function. Here, we solved the crystal structures of Gal-10 and eight variants at resolutions of 1.55-2.00 Å. Structural analysis and size exclusion chromatography demonstrated that Gal-10 dimerizes with a novel global shape that is different from that of other prototype galectins (e.g., Gal-1, -2 and -7). In the Gal-10 dimer, Glu33 from one subunit modifies the carbohydrate-binding site of another, essentially inhibiting disaccharide binding. Nevertheless, glycerol (and possibly other small hydroxylated molecules) can interact with residues at the ligand binding site, with His53 being the most crucial for binding. Alanine substitution of the conserved Trp residue (Trp72) that is crucial to saccharide binding in other galectins, actually leads to enhanced erythrocyte agglutination, suggesting that Trp72 negatively regulates Gal-10 ligand binding. Overall, our crystallographic and biochemical results provide insight into Gal-10 ligand binding specificity.

Charcot-Leyden crystal protein/galectin-10 interacts with cationic ribonucleases and is required for eosinophil granulogenesis

“…65,66 In addition, recent findings indicate that Gal-10 dimerizes with a novel global shape that is different from that of other prototype galectins (eg, Gal-1, Gal-2, and Gal-7) and may essentially inhibit disaccharide binding. 65,67 The lack of binding to ß-galactosides FIG 6. CLC/Gal-10-deficient (knockdown) eosinophils have fewer secondary granules, a nonproliferative phenotype, decreased MBP-1 expression, and increased secretion of EDN in response to PAF stimulation.…”

A Brief History of Charcot-Leyden Crystal Protein/Galectin-10 Research

“…In the asymmetric unit of the Gal-10 crystal, there is only one Gal-10 monomer, a pseudomorph that did not accurately display the global form of Gal10. Actually, Gal-10 is a homodimeric protein in solution [ 25 ].…”

“…A solid phase assay showed that Gal-10 could bind weakly to lactose and n -acetyl- d -glucosamine conjugated to agarose [ 23 , 26 ]. However, three contradictory results showed that the weak carbohydrate binding activity may be attributed to wild type Gal-10 binding to the cross-linked agarose (or Sepharose) matrix and not to lactose [ 19 , 25 , 27 ], and the crystal structure of Gal-10 showed that it could bind mannose [ 23 ]. Recently, we generated a variant of Gal-10 (W127A) that exists as a monomer and can weakly bind to lactose-modified Sepharose [ 28 ].…”

“…The first structure of Gal-10, solved by using Gal-10 purified from a human myeloid leukemic cell line [ 23 ], showed that there is only one Gal-10 monomer in each asymmetric unit. Recently, we and Kamitori used PISA to predict interactions between two Gal-10 CRDs in two separate asymmetric units close in proximity and proposed that Gal-10 may dimerize [ 25 , 40 ]. This model of Gal-10 has a S-face to S-face structure and is significantly different from other prototype galectins ( Figure 2 ).…”

“…This model of Gal-10 has a S-face to S-face structure and is significantly different from other prototype galectins ( Figure 2 ). Gel filtration validated the formation of Gal-10 dimers in solution [ 25 ]. In addition, a key residue (Trp127) helps mediate Gal-10 dimerization [ 28 ].…”