Configurational distribution of denatured phosphoglycerate kinase

Physiochemical characterization of the denatured states of proteins is important for a complete understanding of the factors stabilizing their folded conformations. Using a combination of small angle neutron scattering (SANS), statistical mechanical modelling and molecular mechanics calculations, we examine the configurational distribution of phosphoglycerate kinase denatured in 4 M guanidine hydrochloride solution. The denaturing of the protein produces a clear change in the form of the SANS profile and a large increase of the radius of gyration. In the statistical mechanical model, the region of contrast neutron scattering density associated with the protein is pictured as a chain of freely jointed spheres. The model is fitted to the SANS data for the denatured protein. It is found that a model with a small number of spheres cannot account for the higher resolution scattering, indicating an absence of detectable structuration; a good fit is found with 100 spheres of 8.5 A radius. Single configurations of the fitted chain of spheres are used as low-resolution bounds for model-building and molecular mechanics calculations to obtain plausible atomic-detail models of the denatured chain.