TABLE 1.

Interface residue binding energy contributions and hydrogen bonds observed between αKL1 and α2-3-sialyllactose during the simulations^a

Residue	ΔGbinding (kcal/mol)b	Hydrogen bond partner	Residue	ΔGbinding (kcal/mol)b	Hydrogen bond partner
Ser115	−0.3 ± 0.3		Glu414	0.7 ± 0.4	Sialic acid
Leu117	−0.4 ± 0.5		Gly416	−0.1 ± 0.1
Trp194	−1.0 ± 0.4		Trp417	−0.5 ± 0.4
Asn239	−0.8 ± 0.2	Sialic acid	Phe418	−1.2 ± 0.6
Tyr241	−0.6 ± 0.3		Trp458	−0.3 ± 0.3
Val242	−1.3 ± 0.5		Glu465	0.4 ± 0.3
His246	−1.4 ± 0.2		His467	−1.9 ± 1.1	Galactose
Leu253	−0.6 ± 0.4		Arg468	−2.9 ± 1.1	Glucose, sialic acid
Ser299	−0.1 ± 0.5	Sialic acid	Arg474	−1.6 ± 0.7	Sialic Acid
Gly372	−0.5 ± 0.3		Total	−18.1 ± 2.0
Pro373	−0.5 ± 0.2
Thr374	−0.2 ± 0.5		Glucose*	−7.3 ± 1.4*	Arg468*
Leu375	−0.7 ± 0.6		Galactose*	−3.7 ± 0.6*	His467*
Phe377	−1.4 ± 0.9		Sialic acid*	−13.9 ± 1.6	Asn239*, Ser299*, Glu414*, Arg468*, Arg474*
Leu379	−0.6 ± 0.8		Total*	−25.0 ± 2.8*

^aThe binding energy contribution of the interface residues between αKL1 and α2-3-sialyllactose; hydrogen bonds are reported if present in at least 2 simulations for ≥50% of the analyzed trajectory. The interface residues are defined as those that had a mean heavy-heavy atom distance of <5 Å in at least 3 of the 4 simulations.

^bThe binding free energy was decomposed in 2 ways. One is per amino acid residue, which gives rise to a total ΔG_binding = −18.1 ± 2.0 kcal/mol. The other (*) is per sugar unit, which gives rise to a total ΔG_binding = −25 ± 2.8 kcal/mol. Note that the 2 totals are not identical because the electrostatic salvation energies cannot be equally divided between the receptor and ligand and only the interface residues within 5 Å were included in the first calculation (some long-range electrostatic interactions were not included). Arg468 makes [³H] bonds with α2-3-sialyllactose (2 with sialic acid, 1 with glucose), and contributes to the largest single residue binding energy (−2.9 ± 1.1 kcal/mol). Mutation of this residue disrupts sKlotho regulation of TRPC6 (9).