To understand why the classical two-state allosteric model of Monod, Wyman, and Changeux explains cooperative oxygen binding by hemoglobin but does not explain changes in oxygen affinity by allosteric inhibitors, we have investigated the kinetic properties of unstable conformations transiently trapped by encapsulation in silica gels. Conformational trapping reveals that after nanosecond photodissociation of carbon monoxide a large fraction of the subunits of the T quaternary structure has kinetic properties almost identical to those of subunits of the R quaternary structure. Addition of allosteric inhibitors reduces both the fraction of R-like subunits and the oxygen affinity of the T quaternary structure. These kinetic and equilibrium results are readily explained by a recently proposed generalization of the Monod–Wyman–Changeux model in which a preequilibrium between two functionally different tertiary, rather than quaternary, conformations plays the central role.

New insights into allosteric mechanisms from trapping unstable protein conformations in silica gels / Viappiani, Cristiano; Bettati, Stefano; Bruno, Stefano; Ronda, Luca; Abbruzzetti, Stefania; Mozzarelli, Andrea; W. A., Eaton. - In: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA. - ISSN 0027-8424. - 101:(2004), pp. 14414-14419. [10.1073/pnas.0405987101]

New insights into allosteric mechanisms from trapping unstable protein conformations in silica gels.

VIAPPIANI, Cristiano;BETTATI, Stefano;BRUNO, Stefano;RONDA, Luca;ABBRUZZETTI, Stefania;MOZZARELLI, Andrea;
2004

Abstract

To understand why the classical two-state allosteric model of Monod, Wyman, and Changeux explains cooperative oxygen binding by hemoglobin but does not explain changes in oxygen affinity by allosteric inhibitors, we have investigated the kinetic properties of unstable conformations transiently trapped by encapsulation in silica gels. Conformational trapping reveals that after nanosecond photodissociation of carbon monoxide a large fraction of the subunits of the T quaternary structure has kinetic properties almost identical to those of subunits of the R quaternary structure. Addition of allosteric inhibitors reduces both the fraction of R-like subunits and the oxygen affinity of the T quaternary structure. These kinetic and equilibrium results are readily explained by a recently proposed generalization of the Monod–Wyman–Changeux model in which a preequilibrium between two functionally different tertiary, rather than quaternary, conformations plays the central role.
New insights into allosteric mechanisms from trapping unstable protein conformations in silica gels / Viappiani, Cristiano; Bettati, Stefano; Bruno, Stefano; Ronda, Luca; Abbruzzetti, Stefania; Mozzarelli, Andrea; W. A., Eaton. - In: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA. - ISSN 0027-8424. - 101:(2004), pp. 14414-14419. [10.1073/pnas.0405987101]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11381/2298556
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