Structural Studies on Different Ligand Binding Ability of Sialoadhesin Using Molecular Modeling Techniques

Siglecs are the major homologous subfamily of I-type lectins with an ability to recognize sialylated glycans. Siglecs are attractive therapeutic targets because of their endocytic properties, ability to modulate receptor signaling and cell-type specific expression pattern. Sialoadhesin (Sn/ Siglec-1/ CD169), a member of the Siglec family expressed on subsets of resident and inflammatory macrophages and involves in modulation of inflammation and immunity. In this work, 3-D structure of human Siglec-1 (hSiglec-1) was predicted based on X-ray crystallo-graphically determined structure of mouse Siglec-1[mSiglec-1(PDB ID: 1QFP)] using molecular modeling techniques. The structure of complexes in solution of hSiglec-1 with ligands, glycopeptide and 3′-sialyllactose were predicted using a novel docking technique comprising of repeated cycles of molecular dynamics and energy minimization. Calculation of the free energies of binding of complexes suggested that glycopeptide can form stable complex with dissociation constant value of 3.31 μM whereas complex formation of 3′-sialyllactose with the protein in aqueous medium is thermodynamically unfavorable. The structural analysis of theses complexes represent the functional recognition interactions of this protein with the bound sugar molecule and as such provide detailed information about functional roles of such sugar binding protein.