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Lookup NU author(s): Professor Steve Homans
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We report here solution NMR relaxation measurements that show millisecond time-scale intersubunit dynamics in the homopentameric B subunit (VTB) of the toxin derived from Escherichia coli O157. These data are consistent with interconversion between an axially symmetric form and a low-abundance (10%, 45 °C) higher energy form. The higher energy state is depopulated on binding of a novel bivalent analogue (Pk dimer) of the natural carbohydrate acceptor globotriaosylceramide. The isothermal titration calorimetry isotherm for the binding of Pk dimer to VTB is consistent with a five-site sequential binding model which assumes that cooperative effects arise through communication only between neighboring binding sites. The resulting thermodynamic parameters (Ka1 = 114 ± 2.2 M-1, Ka2 = 283 ± 4.5 M-1, ΔH1° = −116.3 ± 0.55 kJ/mol, and ΔH2° = −50.3 ± 0.11 kJ/mol) indicate favorable entropic cooperativity that has not previously been observed in multivalent systems.
Author(s): Yung A, Turnbull WB, Kalverda AP, Thompson GS, Homans SW, Kitov P, Bundle DR
Publication type: Article
Publication status: Published
Journal: Journal of the American Chemical Society
Year: 2003
Volume: 125
Issue: 43
Pages: 13058-13062
ISSN (print): 0002-7863
ISSN (electronic): 1943-2984
Publisher: American Chemical Society
URL: http://dx.doi.org/10.1021/ja0367288
DOI: 10.1021/ja0367288
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