Around a quarter of the human population is infected by parasitic helminths and this places a large economic burden on the agricultural industry. Unfortunately anthelmintic resistance is a growing problem. Helminths survive long periods of hypoxia in their hosts, but their anaerobic metabolism has yet to be fully characterized. These anaerobic metabolic pathways are a promising, selective target for new drugs. Fumarate reduction, a rewiring of the TCA cycle, has long been identified as a key pathway for parasitic worms. We have previously identified the metabolic pathway for the synthesis of the essential small molecule involved in fumarate respiration, rhodoquinone (RQ) which combines two important pathways, the kynurenine metabolism pathway and the ubiquinone synthesis pathway and found that COQ-2 is the key connection between both. We have previously found that a mutually exclusive exon in
coq-2 which is exclusive to RQ-species is what determines whether RQ or the closely related ubiquinone (UQ) is synthesized.
coq-2 has two key residues near the active site which are conserved in RQ-species but not in other invertebrates or in hosts. Furthermore, mutating these two residues is sufficient to change the UQ-exon so that it can recover in a RQ assay developed by our lab. This finding combined with previous research which suggested that parasitic worms rely on extensive rewiring of existing pathways led to a focus on known metabolites and known pathways which often have existing drugs and crystal structures. By building from previous work, drug targets can be more easily found than if a novel pathway had to be characterized. The most effective drug targets will be those genes which are funadamental to parasitic metabolism and which have had divergence between hosts and parasites so that they can be targeted selectively. More specifically, four pathways which have been previously linked with anaerobic metabolism were tested for importance in RQ-dependent metabolism to narrow down to specific targets. For each of these targets, protein sequences were compared between hosts, parasites and RQ-containing mollusks and annelids to find conserved divergent residues in proximity to druggable sites. In total four known enzymes, including COQ2, have been found which are required for RQ-dependent metabolism and which have parasite specific residues near active sites which may act as selective drug targets. Humanized mutants have been generated for those residues. Moving forwards, in silico drug design will be carried out to find drugs predicted to be specific to the helminths which can be then be assayed against wild-type as well as the humanized mutants.