Table 4.

Changes in the hydrogen bond distances due to a change in the position-orientation of galactose in the binding site of S-lectin and S-Lac lectin

	Distance (in Å)
Hydrogen bond	In observed position-orientationa	In modified position-orientationb
In S-Lectin–Galactose complex
Gal:C2-OH...His52:Nɛ2	4.1	4.8
Gal:C4-OH...His44:Nɛ2	2.8	3.2
Gal:Ring O...Arg48:Nη2	2.9	3.8
Gal:C6-OH...Asn61:Nδ2	2.7	2.3
Gal:C6-OH...Glu71:Oɛ2	2.8	3.0
In S-Lac lectin–Galactose complex
Gal:C3-OH...Arg120:Nη2	3.4	4.8
Gal:C4-OH...His45:Nɛ2	2.8	3.5
Gal:Ring O...Arg49:Nη1	4.0	4.5
Gal:C6-OH...Asn58:Nδ2	2.7	1.9
Gal:C6-OH...Glu68:Oɛ1	2.6	2.9

^a This refers to the position-orientation of galactose relative to the binding site aromatic residue observed in the X-ray crystallographic structure. In S-lectin–galactose complex (PDB ID 1SLT), position (r, θ, θ) = (5.1, 150, -3), and orientation (Φ,Θ,Ψ) = (19, 64, 209). In S-lac lectin–galactose complex (PDB ID 1HLC), position (r, θ, φ) = (4.9, 143, 5), and orientation (Φ,Θ,Ψ) = (37, 48, 199).

^b In the modified position-orientation, (r, θ, φ) = (4.7, 152, -15) and (Φ,Θ,Ψ) = (29, 50, 191). This is the position-orientation observed for galactose in the toad ovary galectin–galactose complex (PDB ID 1GAN).