Total Chemical Synthesis of Onconase and its Sec-Containing Analogs and their Oxidative Folding

Onconase (ONC) is the smallest member of the bovine pancreatic ribonuclease A superfamily, isolated from the oocytes of the Northern leopard frog Rana pipiens. ONC is 104 amino acids long with eight cysteine residues that form four disulfide bonds in the native folded state.¹ The oxidative folding mechanism of ONC is unique, which is a combination of the folding mechanism of two disulfide-rich protein models, that of bovine pancreatic trypsin inhibitor (BPTI) and hirudin.² We will study the effect of cysteine (Cys) to selenocysteine (Sec) substitution on the oxidative folding mechanism of ONC. The unique chemistry Sec, which we have recently deeply investigated, suggest that Cys-to-Sec substitution will increases the yield of the native structure of disulfide-rich protein and enhances protein’s stability.³ In addition, we anticipate that Cys-to-Sec substitution may be used to steer the oxidative folding mechanism to only BPTI-like or hirudin-like mechanism, not a combination of both. The total chemical synthesis of ONC and its Sec-containing analogs based on Fmoc-SPPS and NCL will be presented.

References

[1] Xu, G., Narayan, M., Welker, E. and Scheraga, H.A., 2004. Characterization of the fast-forming intermediate, des [30− 75], in the reductive unfolding of onconase. Biochemistry, 43(11), pp.3246-3254.

[2] Gahl, R.F. and Scheraga, H.A., 2009. Oxidative folding pathway of onconase, a ribonuclease homologue: insight into oxidative folding mechanisms from a study of two homologues. Biochemistry, 48(12), pp.2740-2751.

[3] Metanis, N., Mousa, R. and Notis Dardashti, R., 2017. Selenium and Selenocysteine in Protein Chemistry. Angewandte Chemie.