Bundle DR

Homans SW

Kalverda AP

Kitov P

Thompson GS

Turnbull WB

Yung A

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 \ub0C) 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 \ub1 2.2 M-1, Ka2 = 283 \ub1 4.5 M-1, ΔH1\ub0 = −116.3 \ub1 0.55 kJ/mol, and ΔH2\ub0 = −50.3 \ub1 0.11 kJ/mol) indicate favorable entropic cooperativity that has not previously been observed in multivalent systems

Large-scale millisecond intersubunit dynamics in the B subunit homopentamer of the toxin derived from Escherichia coli O157

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