Exploring the oxidative folding of totally chemically synthesized Onconase and its seleno-analogs

Onconase (ONC) was isolated from the oocytes of the northern leopard Rana pipiens.It is a member of the bovine pancreatic ribonuclease A superfamily and it is the smallest member in the family. ONC contains eight cysteine (Cys) that forms four disulfide bonds in its native folded form. Its oxidative folding pathway is unique as it is a combination of the folding pathways of two cysteine-rich protein models, the hirudin and bovine pancreatic trypsin inhibitor (BPTI).Using the unique chemistry of selenocysteine (Sec), in this project we aim to study the effect of Cys-to-Sec substitutions on the oxidative pathway of ONC. Based on the proposed oxidative folding of ONC, we anticipate that specific Sec substitution will steer the folding pathway of ONC to either only BPTI-like or only hirudin-like, not a combination of both, by this approach a protein folding pathway can be designed. The total chemical synthesis of ONC and its seleno-analogues using Fmoc-SPPS chemistry and NCL will be presented.