Isolating cyclic peptides from linear peptides
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Ballout, Kendah, Mandpaka, Hyma and Wu, Haifan. Isolating cyclic peptides from linear peptides. -- Fyre in STEM Showcase, 2023.
For decades, medicines treating ailments from autoimmune diseases to fungal infections have included peptides. Cyclic peptides are preferable to linear peptides because they are less likely to denature within the body. Purification always follows the cyclization process as some linear peptides fail to cyclize. However, peptide libraries, which can include hundreds of peptides of varying sequences, are difficult to purify with existing methods. Using a process inspired by native chemical ligation (NCL), this project aims to create an effective way to purify cyclic peptides. NCL was developed in the 1990s to create dipeptides. A peptide with a C-terminal thioester reacts with another peptide's nucleophilic N-terminal cysteine to bind the two ends together. This is only possible with linear peptides, as cyclic peptides lack an N-terminus. We hypothesize that linear peptides would bind to a solid thioester resin while cyclic peptides remain in the liquid solution. The first stage of the project, synthesizing a thioester resin from a carboxylic acid, requires an intermediate step: creating a hydrazide resin. Once UV spectroscopy confirmed that was successful, a thioester could be obtained by reacting it with sodium nitrite and MPAA. A mixture of linear and cyclic peptides and MPAA were added to the resin simultaneously and a small amount of the liquid solution was analyzed with HPLC after a few hours. Results indicated that the linear peptide was no longer in the solution, but the cyclic peptides remained there. These findings will facilitate the purification of peptide mixtures and studying peptide libraries.
Poster and abstract presented at the FYRE in STEM Showcase, 2023.
Research project completed at the Department of Chemistry and Biochemistry.