Identification of Atg-8–Atg 3 protein-protein interaction inhibitor

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SELECTBIO

Autophagy is a catabolic process of normal cells to maintain homeostasis and degradation of unwanted and toxic cellular content such as misfolded proteins. A key protein of this pathway is Atg8 (MAP1LC3), a ubiquitin-like autophagy protein in eukaryotes that is covalently attached (lipidated) to the autophagosome membrane. Autophagy is appreciated as a target in diverse diseases from cancer to eukaryotic parasitic infections. Some of the autophagy machinery is conserved in the malaria parasite, Plasmodium; the best-characterized autophagy protein in P. falciparum (Pf) is Atg8, with a known co-crystal structure of Atg8 with a peptide from it’s E2 conjugating enzyme Atg3. Although Atg8's function in the parasite is not well understood, it is essential for Plasmodium growth and survival and partially localizes to the apicoplast, an indispensable organelle in Apicomplexans. Here we describe the identification of inhibitors from the Malaria Medicine Venture (MMV) Malaria Box against the protein-protein interaction of PfAtg8 with its E2-conjugating enzyme, PfAtg3 by surface plasmon resonance (SPR). These small molecule inhibitors share a common scaffold and have activity against both blood and liver stages of infection by P. falciparum. The inhibition of the interaction between Atg3 and Atg8 results in the non-lipidated form of Atg8, rendering autophagosome expansion dysfunctional. We have derivatized this scaffold into a functional platform, while retaining activity for further optimization.