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.
Yung
Anna
A
Astbury Centre for Structural Molecular Biology, School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom.
Turnbull
W Bruce
WB
Kalverda
Arnout P
AP
Thompson
Gary S
GS
Homans
Steve W
SW
Kitov
Pavel
P
Bundle
David R
DR
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