EXCLUDED-VOLUME IN THE CONFIGURATIONAL DISTRIBUTION OF A STRONGLY-DENATURED PROTEIN

The configurational distribution of phosphoglycerate kinase (PGK) stro ngly-denatured in 4M guanidine hydrochloride solution is investigated using small-angle neutron scattering (SANS) and Monte Carlo computer s imulation. It is shown that the experimental scattering profile can be represented by a random flexible chain of spheres of excess scatterin g density with excluded volume interactions, the best agreement being achieved when partial sphere intersection is allowed. The radius of gy ration of the chain increases by a factor of 4 on denaturation, wherea s the average length of segments similar to 5 residues long increases by only similar to 10%, consistent with a picture in which the large e xpansion on denaturation originates primarily from increased long-rang e flexibility of the polypeptide chain. The results provide a descript ion of the chain statistics from which the construction of starting po ints for simulation studies of folding of the protein can be envisaged .