Large-scale millisecond intersubunit dynamics in the B subunit homopentamer of the toxin derived from Escherichia coli O157.
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 ( approximately 10%, 45 degrees C) higher energy form. The higher energy state is depopulated on binding of a novel bivalent analogue (P(k) dimer) of the natural carbohydrate acceptor globotriaosylceramide. The isothermal titration calorimetry isotherm for the binding of P(k) 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 (K(a1) = 114 +/- 2.2 M(-1), K(a2) = 283 +/- 4.5 M(-1), DeltaH(1) degrees = -116.3 +/- 0.55 kJ/mol, and DeltaH(2) degrees = -50.3 +/- 0.11 kJ/mol) indicate favorable entropic cooperativity that has not previously been observed in multivalent systems.
Astbury Centre for Structural Molecular Biology, School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom.
Anna
A
Yung
W Bruce
WB
Turnbull
Arnout P
AP
Kalverda
Gary S
GS
Thompson
Steve W
SW
Homans
Pavel
P
Kitov
David R
DR
Bundle
D019453:Escherichia coli O157 / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D021122:Protein Subunits / Q000737:chemistry*; D022641:Shiga Toxin 2 / Q000737:chemistry*; D013816:Thermodynamics
D021122:Protein Subunits; D022641:Shiga Toxin 2; C450841:shiga toxin 2 B subunit