Activity–structure correlations in divergent lectin evolution: fine specificity of chicken galectin CG-14 and computational analysis of flexible ligand docking for CG-14 and the closely related CG-16

Abstract

Gene duplication and sequence divergence are driving forces toward establishing protein families. To examine how sequence changes affect carbohydrate specificity, the two closely related proto-type chicken galectins CG-14 and CG-16 were selected as models. Binding properties were analyzed using a highly sensitive solid-phase assay. We tested 56 free saccharides and 34 well-defined glycoproteins. The two galectins share preference for the II (Galb1-4GlcNAc) versus I (Galb1-3GlcNAc) version of b-galactosides. A pronounced difference is found owing to the reactivity of CG-14 with histo-blood group ABH active oligosaccharides and A/B active glycoproteins. These experimental results prompted to determine activitystructure correlations by modeling. Computational analysis included consideration of the flexibility of binding partners and the presence of water molecules. It provided a comparative description of complete carbohydrate recognition domains, which had so far not been characterized in animal galectins. The structural models assigned II, I selectivity to a region downstream of the central Trp moiety. Docking revealed that the tetrasaccharides can be accommodated in their free-state low-energy conformations. CG-14's preference for A versus B epitopes could be attributed to a contact between His124 and the Nacetyl group of GalNAc. Regarding intergalectin comparison, the Ala53/Cys51 exchange affects the interaction potential of His54/His52. Close inspection of simulated dynamic interplay revealed reorientation of His124 at the site of the His124/Glu123 substitution, with potential impact on ligand dissociation. In summary, this study identifies activity differences and provides information on their relation to structural divergence, epitomizing the value of this combined approach beyond galectins.

Assessing the inhibitory potency of galectin ligands identified from combinatorial (glyco)peptide libraries using surface plasmon resonance spectroscopy

“…The further structural analysis of these complexes may disclose peptide-galectin contacts beyond the central lactose moiety. Whether they involve sites of the lectin active in binding of histo-blood group A/B-tetrasaccharides or the ganglioside GM1-derived pentasaccharide [29,30] is an open question. …”

Bi- to tetravalent glycoclusters: synthesis, structure–activity profiles as lectin inhibitors and impact of combining both valency and headgroup tailoring on selectivity

“…11a,26 Occurrence of intrafamily differences between CGs was further underscored by slight enhancement of reactivity for CG-8 10 and reduced sensitivity to α1,2-or α1,3-substitutions seen for CG-1B relative to CG-1A. 9 Scheme 2 The comprehensive profiling of lectin reactivity to 1-7 singled out the chimera-type lectin as the most responsive (Table 1). The CG-3 was especially reactive with FL and found to be susceptible to an increase in valency, with the highest affinity being observed towards 6 (Table 1).…”

“…Amberlite IR-120 ( plus) was added to neutralize ( pH = 7), whereafter the resin was removed by filtration and washed with water. The solvent was removed and the residue was purified by BioGel P-2 gel filtration column to give 4 as an amorphous solid 124.3, 102.9, 95.8, 87.2, 77.6, 77.3, 75.3, 74.5, 72.4, 71.9, 70.9, 68.5 9,75.6,72.7,70.9,70.8,70.5,69.1,66.6 (each CH),61.8,60.8,50.9,36.6,35.9,28.6,25.2,25.0,24.5 (each CH 2 ),20.9,20.74,20.67,20.65,20.64,20.5,20.3 …”

Human galectins as sensors for apoptosis/necrosis‐associated surface changes of granulocytes and lymphocytes

“…The following physiological precedents illustrate the relevance of desialylation or downregulation of sialylation as switch-on mechanism for galectin activity: the transition from prolifera- tion to differentiation/anoikis in neuroblastoma or pancreatic cancer cells is linked to a decrease in cell surface sialylation, and a member of the galectin family acts as sensor and effector in both cases (27,31,42). Beyond the sialylation status, the binding activity of these endogenous lectins is also sensitive to changes in the structure of the b-galactoside beyond the central galactose unit, the degree and type of core substitutions, and the density of glycan presentation (14)(15)(16)(17)43). The latter factor can modulate ligand properties without any requirement for a change in the glycan sequence.…”