Galectin-13, a different prototype galectin, does not bind β-galacto-sides and forms dimers via intermolecular disulfide bridges between Cys-136 and Cys-138

Abstract

During pregnancy, placental protein-13 (galectin-13) is highly expressed in the placenta and fetal tissue, and less so in maternal serum that is related to pre-eclampsia. To understand galectin-13 function at the molecular level, we solved its crystal structure and discovered that its dimer is stabilized by two disulfide bridges between Cys136 and Cys138 and six hydrogen bonds involving Val135, Val137, and Gln139. Native PAGE and gel filtration demonstrate that this is not a crystallization artifact because dimers also form in solution. Our biochemical studies indicate that galectin-13 ligand binding specificity is different from that of other galectins in that it does not bind β-galactosides. This is partly explained by the presence of Arg53 rather than His53 at the bottom of the carbohydrate binding site in a position that is crucial for interactions with β-galactosides. Mutating Arg53 to histidine does not re-establish normal β-galactoside binding, but rather traps cryoprotectant glycerol molecules within the ligand binding site in crystals of the R53H mutant. Moreover, unlike most other galectins, we also found that GFP-tagged galectin-13 is localized within the nucleus of HeLa and 293 T cells. Overall, galectin-13 appears to be a new type of prototype galectin with distinct properties.

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

“…was also recently demonstrated for 1 other galectin family member, galectin-13, which exhibits approximately 54% amino acid identity with CLC/Gal-10. 68 Our results further show that CLC/Gal-10 interacts with the glycosylated human eosinophil granule cationic RNases, EDN (RNS2) and ECP (RNS3), but this interaction is not dependent on binding via N-or O-linked sugars, and it occurs even with bacterially expressed recombinant EDN devoid of any glycosylation. Of interest, CLC/Gal-10 also binds avidly to the large family of murine EARs, despite the lack of a CLC/Gal-10 ortholog in the mouse genome.…”

Selection scan reveals three new loci related to high altitude adaptation in Native Andeans

“…Investigations with galectin paralogues have shown that galectin-1 in the first term ovine gestation placenta prevented inflammatory processes that harm the fetus 55 , while galectin-13, which has the highest homology to CLC, is a member of the group of the so-called “pregnancy-related proteins”, due to its special immune functions at the feto-maternal interface 56 , 57 . These fundamental cell functions, already described for humans and other placental mammals, may indicate the path that connects our CLC findings and the selection pressure in the Andean hostile climate.…”

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

“…Although the structures of some prototype galectins (i.e. galectin-14, -16 and -17) have yet to be reported, most prototype galectin structures are known [ 34 , 53 , 54 , 55 , 56 ]. Crystallographic and biochemical analyses show that Gal-1, -2, -7 and -10 form dimers via non-covalent interactions [ 34 , 53 , 54 , 55 ].…”

“…Gal-13 is an unusual prototype galectin in that it forms dimers via disulfide bonds formed between two cysteine residues (Cys136 and Cys138) at the C-terminus of its CRD [ 56 ]. A variant with two mutations (C136S/C138S) exists as a monomer in solution [ 56 ].…”

“…Gal-13 is an unusual prototype galectin in that it forms dimers via disulfide bonds formed between two cysteine residues (Cys136 and Cys138) at the C-terminus of its CRD [ 56 ]. A variant with two mutations (C136S/C138S) exists as a monomer in solution [ 56 ]. Hemagglutination assays have shown that DTT could inhibit this variant inducing erythrocyte agglutination, indicating that the Gal-13 dimer structure is crucial to its function.…”