Microcalorimetric study of wheat germ agglutinin binding to N-acetylglucosamine and its oligomers

Gabrielle Bains, Reiko T. Lee, Yuan C. Lee, Ernesto I Freire

Research output: Contribution to journalArticle

Abstract

The energetics of association of wheat germ agglutinin (WGA) with N-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 TΔS 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 in 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.

Original languageEnglish (US)
Pages (from-to)12624-12628
Number of pages5
JournalBiochemistry®
Volume31
Issue number50
StatePublished - 1992

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Wheat Germ Agglutinins
Acetylglucosamine
Oligomers
Titration
Enthalpy
Protonation
Calorimetry
Deprotonation
Buffers
Binding Sites
Association reactions

ASJC Scopus subject areas

  • Biochemistry

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Microcalorimetric study of wheat germ agglutinin binding to N-acetylglucosamine and its oligomers. / Bains, Gabrielle; Lee, Reiko T.; Lee, Yuan C.; Freire, Ernesto I.

In: Biochemistry®, Vol. 31, No. 50, 1992, p. 12624-12628.

Research output: Contribution to journalArticle

Bains, Gabrielle ; Lee, Reiko T. ; Lee, Yuan C. ; Freire, Ernesto I. / Microcalorimetric study of wheat germ agglutinin binding to N-acetylglucosamine and its oligomers. In: Biochemistry®. 1992 ; Vol. 31, No. 50. pp. 12624-12628.
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