Controlling protein stability: Mechanisms revealed using formulations of arginine, glycine and guanidinium HCl with three globular proteins.

Three distinct interactions between the amino acid arginine and a protein explain arginine's ability to modulate the thermal stability of proteins. Arginine's effect on the protein unfolding behaves like the sum of its constituent parts, glycine and the guanidinium ion. The authors propose that glycine can affect the thermal stability of a protein in two ways: (1) direct interaction with the charged side chains and/or the peptide backbone of the protein which is observed at low concentrations and (2) competition for water between the unfolding protein and the cosolute increasing the energy required to hydrate the unfolding protein. The guanidinium ion acts by (3) direct interaction with apolar regions exposed during unfolding reducing the energy required to hydrate the unfolding protein.