De Novo Discovery of Pseudo-Natural Prenylated Macrocyclic Peptide Ligands.

Prenylation of peptides is widely observed in the secondary metabolites of diverse organisms, granting peptides unique chemical properties distinct from proteinogenic amino acids. Discovery of prenylated peptide agents has largely relied on isolation or genome mining of naturally occurring molecules. To devise a platform technology for de novo discovery of artificial prenylated peptides targeting a protein of choice, here we have integrated the thioether-macrocyclic peptide (teMP) library construction/selection technology, so-called RaPID (Random nonstandard Peptides Integrated Discovery) system, with a Trp-C3-prenyltransferase KgpF involved in the biosynthesis of a prenylated natural product. This unique enzyme exhibited remarkably broad substrate tolerance, capable of modifying various Trp-containing teMPs to install a prenylated residue with tricyclic constrained structure. We constructed a vast library of prenylated teMPs and subjected it to in vitro selection against a phosphoglycerate mutase. This selection platform has led to the identification of a pseudo-natural prenylated teMP inhibiting the target enzyme with an IC50 of 30 nM. Importantly, the prenylation was essential for the inhibitory activity, enhanced serum stability, and cellular uptake of the peptide, highlighting the benefits of peptide prenylation. This work showcases the de novo discovery platform for pseudo-natural prenylated peptides, which is readily applicable to other drug targets.

A Macrocyclic Peptide Library with a Structurally Constrained Cyclopropane-containing Building Block Leads to Thiol-independent Inhibitors of Phosphoglycerate Mutase.

Here we report the construction of an mRNA-encoded library of thioether-closed macrocyclic peptides by using an N-chloroacetyl-cyclopropane-containing exotic initiator whose structure is more constrained than the ordinary N-chloroacetyl-α-amino acid initiators. The use of such an initiator has led to a macrocycle library with significantly suppressed population of lariat-shaped species compared with the conventional libraries. We previously used a conventional library and identified a small lariat thioether-macrocycle with a tail peptide with a C-terminal free Cys whose sidechain plays an essential role in potent inhibitory activity against a parasitic model enzyme, phosphoglycerate mutase. On the other hand, the cyclopropane-containing macrocycle library has yielded a larger thioether-macrocycle lacking a free Cys residue, which exhibits potent inhibitory activity to the same enzyme with a different mode of action. This result indicates that such a cyclopropane-containing macrocycle library would allow us to access mechanistically distinct macrocycles.