TY - JOUR
T1 - Microcalorimetric Study of Wheat Germ Agglutinin Binding to N-Acetylglucosamine and Its Oligomers
AU - Bains, Gabrielle
AU - Lee, Reiko T.
AU - Lee, Yuan C.
AU - Freire, Ernesto
PY - 1992/2/1
Y1 - 1992/2/1
N2 - The energetics of association of wheat germ agglutinin (WGA) with TV-acetylglucosamine (GlcNAc) and its β(1, 4) oligomers have been measured using isothermal titration calorimetry. Association constants of 0.4, 5.3, 11.1, 12.3, and 19.1 mM−1 and enthalpies of binding of-6.1, -15.6, -19.4, -19.3, and -18.2 kcal mol−1 were obtained at 26 °C for the titration of WGA with GlcNAc, (GlcNAc)2, (GlcNAc)3, (GlcNAc)4, and (GlcNAc)5, respectively. The term TAS was always of negative value, indicating that the binding process is enthalpically driven. Titrations of WGA performed at pH 4.5 did not differ significantly from those performed at pH 7.0, suggesting that no groups with a pKa this range are directly involved in the binding event. Also, performing the titration in a buffer system with a higher enthalpy of protonation did not change the enthalpy of binding confirming that there is no net protonation or deprotonation when WGA binds GlcNAc residues at pH 7. A model of four independent binding sites was found to adequately describe the binding curves, except in the case of (GlcNAc)4 which exhibited positive cooperativity. The energetic values are discussed within the context of the structure of the WGA-(GlcNAc)2 complex.
AB - The energetics of association of wheat germ agglutinin (WGA) with TV-acetylglucosamine (GlcNAc) and its β(1, 4) oligomers have been measured using isothermal titration calorimetry. Association constants of 0.4, 5.3, 11.1, 12.3, and 19.1 mM−1 and enthalpies of binding of-6.1, -15.6, -19.4, -19.3, and -18.2 kcal mol−1 were obtained at 26 °C for the titration of WGA with GlcNAc, (GlcNAc)2, (GlcNAc)3, (GlcNAc)4, and (GlcNAc)5, respectively. The term TAS was always of negative value, indicating that the binding process is enthalpically driven. Titrations of WGA performed at pH 4.5 did not differ significantly from those performed at pH 7.0, suggesting that no groups with a pKa this range are directly involved in the binding event. Also, performing the titration in a buffer system with a higher enthalpy of protonation did not change the enthalpy of binding confirming that there is no net protonation or deprotonation when WGA binds GlcNAc residues at pH 7. A model of four independent binding sites was found to adequately describe the binding curves, except in the case of (GlcNAc)4 which exhibited positive cooperativity. The energetic values are discussed within the context of the structure of the WGA-(GlcNAc)2 complex.
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U2 - 10.1021/bi00165a012
DO - 10.1021/bi00165a012
M3 - Article
C2 - 1472499
AN - SCOPUS:0027098042
SN - 0006-2960
VL - 31
SP - 12624
EP - 12628
JO - Biochemistry
JF - Biochemistry
IS - 50
ER -