High-resolution X-ray analysis reveals binding of arginine to aromatic residues of lysozyme surface: implication of suppression of protein aggregation by arginine

While biotechnological applications of arginine (Arg) as a solution additive that prevents protein aggregation are increasing, the molecular mechanism of its effects remains unclear. In this study, we investigated the Arg–lysozyme complex by high-resolution crystallographic analysis. Three Arg molecules were observed to be in close proximity to aromatic amino acid residues of the protein surface, and their occupancies gradually increased with increasing Arg concentration. These interactions were mediated by electrostatic, hydrophobic and cation–π interactions with the surface residues. The binding of Arg decreased the accessible surface area of aromatic residues by 40%, but increased that of charged residues by 10%. These changes might prevent intermolecular hydrophobic interactions by shielding hydrophobic regions of the lysozyme surface, resulting in an increase in protein solubility.