In Vitro Selection of Macrocyclic <scp>l</scp>-α/<scp>d</scp>-α/β/γ-Hybrid Peptides Targeting IFN-γ/IFNGR1 Protein–Protein Interaction

Abstract

Nonproteinogenic amino acids, including d -α-, β-, and γ-amino acids, present in bioactive peptides play pivotal roles in their biochemical activities and proteolytic stabilities. d -α-Amino acids ( d αAA) are widely used building blocks that can enhance the proteolytic stability. Cyclic β 2,3 -amino acids (cβAA), for instance, can fold peptides into rigid secondary structures, improving the binding affinity and proteolytic stability. Cyclic γ 2,4 -amino acids (cγAA) are recently highlighted as rigid residues capable of preventing the proteolysis of flanking residues. Simultaneous incorporation of all d αAA, cβAA, and cγAA into a peptide is expected to yield l -α/ d -α/β/γ-hybrid peptides with improved stability and potency. Despite challenges in the ribosomal incorporation of multiple nonproteinogenic amino acids, our engineered tRNA Pro1E2 successfully reaches such a difficulty. Here, we report the ribosomal synthesis of macrocyclic l -α/ d -α/β/γ-hybrid peptide libraries and their application to in vitro selection against interferon gamma receptor 1 (IFNGR1). One of the resulting l -α/ d -α/β/γ-hybrid peptides, IB1, exhibited remarkable inhibitory activity against the IFN-γ/IFNGR1 protein–protein interaction (PPI) (IC 50 = 12 nM), primarily attributed to the presence of a cβAA in the sequence. Additionally, cγAAs and d αAAs in the resulting peptides contributed to their serum stability. Furthermore, our peptides effectively inhibit IFN-γ/IFNGR1 PPI at the cellular level (best IC 50 = 0.75 μM). Altogether, our platform expands the chemical space available for exploring peptides with high activity and stability, thereby enhancing their potential for drug discovery.

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