Collaboration with group at University of Parma, Italy, on hemoglobin allostery: Following an extended period of steady state laser illumination of the carbon monoxide complex of hemoglobin in the T quaternary structure to maintain the hemes in the deoxy state, the kinetics of carbon monoxide rebinding after turning off the laser switch from biphasic to monophasic, indicating that all subunits are in the same conformation as deoxyhemoglobin in the absence of light or carbon monoxide. These experiments dramatically confirm our interpretation of gel-encapsulated rebinding kinetics following nanosecond photodissociation of carbon monoxide in the T quaternary structure as arising from an equilibrium population of liganded subunits in the same conformation as found in the R quaternary structure. Preliminary experiments suggest that steady illumination of the carbon monoxide complex prepared in the R quaternary structure results in the appearance of a slow rebinding phase, indicating the formation of T-like tertiary structures in the R quaternary structure - a major prediction of our Tertiary Two-State Allosteric model, and a result that is inconsistent with the two-state model of Monod, Wyman, and Chageux, as well as all other existing theoretical models. A series of control experiments are now being carried out to confirm the discovery of T-like tertiary structures in the R quaternary structure.
|Henry, Eric R; Mozzarelli, Andrea; Viappiani, Cristiano et al. (2015) Experiments on Hemoglobin in Single Crystals and Silica Gels Distinguish among Allosteric Models. Biophys J :|
|Viappiani, Cristiano; Abbruzzetti, Stefania; Ronda, Luca et al. (2014) Experimental basis for a new allosteric model for multisubunit proteins. Proc Natl Acad Sci U S A 111:12758-63|