Zinc Metalloproteases of Apicomplexan Parasites: Conserved Targets for Broad-Spectrum Antiparasitic Drug Discovery.
Abstract
The phylum Apicomplexa includes major protozoan pathogens of humans and animals (Plasmodium falciparum, Toxoplasma gondii, Cryptosporidium parvum, Babesia spp., Eimeria spp., and Neospora caninum) with substantial global health and economic impact. Resistance to key chemotherapeutics, including the partner and antifolate drugs used against several of these diseases, is narrowing a limited arsenal of target-specific treatments, creating an urgent need for mechanistically distinct drug targets. Proteolytic enzymes are attractive candidates, yet antiprotease drug discovery in the Apicomplexa has concentrated on aspartyl and cysteine proteases, leaving zinc metalloproteases (ZMPs) comparatively neglected despite non-redundant roles in haemoglobin digestion, invasion, egress, organelle biogenesis, and immune evasion. This review synthesises the biology, conservation, and drug-target status of apicomplexan ZMPs (MEROPS families M1, M16C, M17, M18, M24, M41) across the six species above. Catalytic-domain conservation, genetic and pharmacological validation status, and inhibitor pharmacology (hydroxamic acid, phosphinic acid, bestatin, amino-benzosuberone, and peptide-based scaffolds) are compared family-by-family. A multi-criteria druggability framework identifies the M17 leucyl aminopeptidase and apicoplast-resident FtsH1 (M41) as the most compelling pan-apicomplexan targets, reflecting genetic essentiality, chemical tractability, and host selectivity, while the expanded M16C insulinase family of C. parvum illustrates a lineage-specific opportunity. Principal gaps include sparse genetic validation outside P. falciparum and T. gondii, near-total absence of experimental structures beyond P. falciparum, and no ZMP inhibitor yet advanced to in vivo or clinical testing. This synthesis aims to advance apicomplexan zinc metalloproteases from an underexplored genomic feature toward a validated class of antiparasitic drug targets.