Efficient refolding and functional characterization of PfAMA1(DI+DII) expressed in E. coli

Chemically Engineered Peptide Efficiently Blocks Malaria Parasite Entry into Red Blood Cells

Chemical peptide engineering, enabled by residue insertion, backbone cyclization, and incorporation of an additional disulfide bond, led to a unique cyclic peptide that efficiently inhibits the invasion of red blood cells by malaria parasites. The engineered peptide exhibits a 20-fold enhanced affinity toward its receptor (PfAMA1) compared to the native peptide ligand (PfRON2), as determined by surface plasmon resonance. In-vitro parasite growth inhibition assay revealed augmented potency of the engineered peptide. The structure of the PfAMA1-cyclic peptide complex, predicted by the deep learning-based structure prediction tool ColabFold-AlphaFold2 with protein-cyclic peptide complex offset, provided valuable insights into the observed activity of the peptide analogs. Rational editing of the peptide backbone and side chain described here proved to be an effective strategy for designing peptide-based inhibitors to interfere with disease-related protein-protein interactions.

Rational engineering of an antimalarial peptide with enhanced proteolytic stability and preserved parasite invasion inhibitory activity

We describe rational chemical engineering to enhance the proteolytic stability of a chimeric peptide using a combination of unique strategies that involve the incorporation of a series of d-amino acids into the parent l-peptide sequence and restricting the conformational freedom of the peptide by covalent stitching. We hypothesize that replacing a stretch of sequence of an unstructured peptide motif with d-amino acids would increase its proteolytic stability without significantly affecting its affinity to the target protein. Also, considering the Cβ-Cβ distances, replacing an appropriate pair of residues with cysteine to form an additional disulfide bond in the molecule would provide additional stability to the engineered peptide. To verify this hypothesis, we have implemented these strategies to a previously reported peptidic inhibitor RR, against P. falciparum invasion into red blood cells (RBCs) and designed two novel heterochiral chimeric peptides, RR-I and RR-II. We have demonstrated that these peptides exhibit remarkable inhibitory activity with dramatically enhanced proteolytic stability. Finally, we have designed a cyclic analog, RR-III, to enhance the stability of the peptide against endopeptidases. The RR-III peptide exhibits the same inhibitory activity as RR-II while demonstrating impressive resistance to enzymatic degradation and prolonged stability in human plasma. These developments hold promise for a new generation of peptide-based therapeutics, showcasing the potential of residue selection for tailored modifications, as demonstrated in this work.