The inverse and direct Hofmeister series of Hen egg lysozyme at pH below isoelectric point (pI) as seen by SAXS

Protein interaction and aggregation processes are important in understanding many physiological processes in living organisms. Diseases such as Alzheimer’s, Creutzfeldt-Jakob and Parkinson’s are associated with protein or peptide aggregation phenomena. We are focused on determining the shape, size, and nature of interactions between the protein molecules (lysozyme) in solution at low and high salt concentration of various sodium salts at certain pH by using Small-angle X-ray scattering (SAXS).
Results show that for protein at 10mg/ml and 200mg/ml the shape and size of the protein is spherical with radius 15.5 Å and 16.7 Å respectively. At 60mg/ml with 0.1M sodium salt, the shape and size of the protein is ellipsoidal with the average polar radius of 38.5 Å and equatorial radius 15.5Å. There is no interaction among proteins at 10mg/ml and 60mg/ml whereas at 200mg/ml we see a coulomb repulsive interaction with effective radius 20.3 Å. The variation of the polar radius of protein at 60mg/ml at pH 9.0 with 0.1M of various Hofmeister sodium salts shows an elongation of the protein as we go from left to right in the Hofmeister series. We are currently focusing on determining the mechanism of elongation and impact on aggregation in the protein induced by Hofmeister salts.