Building Capture Agents for the Detection of Plasmodium Lactate Dehydrogenase (pLDH) as Malaria In Vitro Diagnostics
- James Heath, Elizabeth W. Gilloon Professor of Chemistry, California Institute of Technology
- Aiko Umeda, Postdoctoral Scholar in Chemistry, California Institute of Technology
Conventional protein-detection methods that identify malaria utilize antibodies for their high affinity and selectivity for their target protein; however, these antibodies are expensive and unstable, especially in the presence of thermal fluctuations. As an alternative to traditional antibody-based capture agents, more cost-effective and stable peptide-based multi-ligand protein-capture agents have been developed through the Huisgen 1,3-dipolar cycloaddition reaction and one-bead-one-compound (OBOC) peptide library screens (“in situ click screen”). In this study, a capture agent against pLDH is being constructed based on the in situ click screen strategy. We chose amino acid residues 285-295 of pLDH as a target epitope for general detection of malarial parasites since this epitope is conserved among the major Plasmodium species. We screened a linear 5-mer OBOC library of D-amino acids against the chemically synthesized epitope to isolate the anchor peptide NH2-hevwh-COOH, which showed moderate binding to pLDH in ELISA. Based on these ELISAs, we estimated the dissociation constant to be between 1-20 μM. We then screened the second OBOC library of 5-mer cyclic peptides of L-amino acids using the anchor peptide and full-length pLDH protein. The candidate biligand, hevwh-(YLGHK)cyclic, has been scaled up and is currently being tested for its affinity and selectivity for different strands of pLDH from major Plasmodium species. We expect that peptide-based multi-ligands will serve as drop-in replacements for antibodies as robust capture agents in malaria diagnostics.