Probing Residue-Specific Interactions in the Stabilization of Proteins Using High-Resolution NMR: A Study of Disulfide Bond Compensation

Abstract

It is well established that the oxidation state of cysteine residues in proteins are critical to overall physical stability. The presence of disulfide bonds most often imparts thermodynamic stability, and as such, engineered disulfide bonds have become a means for improving the viability of protein therapeutics. In some cases, however, disulfide bonds can diminish stability. Because proteins are held together by numerous weak interactions, understanding the mechanisms by which stabilization is achieved is important to the design of new biotechnology products that better resist unfolding and aggregation. Mechanistic information describing how specific interactions influence stability is lacking, in part because the techniques typically used to study inherent stability do not provide sufficient detail. In the present study, a model protein system, phosphatase of regenerating liver (PRL-1), was used to investigate the role of cysteine residues on physical stability. A combination of chemical modulation and mutagenesis was employed to alter the redox state of the protein, and the effects were observed using a combination of low- and high-resolution methods. Specifically, solution NMR data revealed the stability of PRL-1 depends on cooperation between local interactions with the Cys side chains. This approach provides a means to better understand how protein stabilization is achieved.