Christopher Grubb, Graduate Student, Meisel Lab, GW Department of Chemistry

The Department of Chemistry Presents:  Christopher Grubb, Graduate Student, Meisel Lab, GW Department of Chemistry.  

Macrocyclic peptides are promising candidates for protein surface recognition because of their large size, precisely displayed functional groups, and structural complexity. However, macrocyclic peptides typically adopt a flat conformation that is poorly suited for binding to convex protein surfaces, such as amino acid residues that protrude from the protein surface as “pillars.” Some recent examples of pillar- binding peptides have emerged from the scientific literature, but binding contributions of pillar residues were not investigated. Supramolecular cavitands have been widely studied as pillar-binding ligands but lack the conformational and functional control that is necessary for strong and selective binding. As a result, the pursuit of rationally designed pillar-binding ligands remains understudied. Cyclic peptide cavitands are synthesized from noncanonical amino acid mimetics and contain a defined pocket that is characteristic of cavitands. Cyclic peptide cavitands possess the synthetic and functional advantages of most cyclic peptides and provide a binding site for convex protein surfaces. However, these cavitands still suffer from structural complexities that make preorganization for binding difficult. As such, controlling the conformation for the rational design of protein surface ligands remains a challenge. In our work we investigate the role of stereosequence – the sequence of stereocenters in an oligomer – in controlling the global conformation of cyclic peptide cavitands. We synthesized a library of cavitands composed of alpha amino acids and meta-aminomethylbenzoic acid (MAMBA) dipeptide mimetics and studied conformational changes that arise from single point alterations in backbone stereochemistry. We found that specific intramolecular hydrogen bonds are critical for transmitting stereochemical information along the macrocyclic backbone. This stereochemical information is
conveyed through the secondary structure of cyclic peptide cavitands. Our findings were then applied to a model protein PTPN1, which contains an allosteric binding site around pillar residue Phe280. Pillar-binding ligands were designed and screened with computational
docking software. Ligands were then synthesized and screened with thermal shift (TSA) and pNPP inhibition assays for affinity and activity toward PTPN1. We found that some allosteric inhibitors of PTPN1 have a destabilizing effect on the melting point of PTPN1, possibly highlighting an unusual
mechanism by which pillar binding ligands interact with protein surfaces. Our ongoing research will provide insight into mechanisms by which chemists can rationally design inhibitors that bind to protein pillars.

BIO

Chris graduated from the University of Montana in Missoula, MT in 2017 with a B.S. in Chemistry. While at UM, Chris worked as an undergraduate researcher with Dr. Orion Berryman working to develop thiourea-based organocatalysts. In 2020, Chris started a PhD at The George Washington University where he joined Dr. Joseph Meisel’s group shortly after. Since then, he has been studying conformational control of peptidomimetic macrocycles.