Identification of enzymes that have helminth-specific active sites and are required for Rhodoquinone-dependent metabolism as targets for new anthelmintics

Abstract

Soil transmitted helminths (STHs) are major human pathogens that infect over a billion people. Resistance to current anthelmintics is rising and new drugs are needed. Here we combine multiple approaches to find druggable targets in the anaerobic metabolic pathways STHs need to survive in their mammalian host. These require rhodoquinone (RQ), an electron carrier used by STHs and not their hosts. We identified 25 genes predicted to act in RQ-dependent metabolism including sensing hypoxia and RQ synthesis and found 9 are required. Since all 9 have mammalian orthologues, we used comparative genomics and structural modeling to identify those with active sites that differ between host and parasite. Together, we found 4 genes that are required for RQ-dependent metabolism and have different active sites. Finding these high confidence targets can open up in silico screens to identify species selective inhibitors of these enzymes as new anthelmintics.

An Organismal Perspective on the Warburg Effect and Models for Proliferation Studies

“…Two critical residues distinguish this exon. Three additional genes associated with an RQ-based anaerobic metabolism were also identified [ 17 ]. As described in more detail below, bioinformatic methods could, thus, be used to search for the signature of anaerobic mitochondria in available genomic data prior to undertaking the necessary experiments to investigate the actual physiology.…”

“…Besides RQ itself, anaerobic mitochondria require several other genetic variants compared to aerobic mitochondria. In particular, variants of three additional genes are associated with an RQ-based anaerobic metabolism [ 17 ]. The best-characterized are those associated with the quinone-binding pocket of succinate dehydrogenase (Complex II) [ 17 ].…”

“…In particular, variants of three additional genes are associated with an RQ-based anaerobic metabolism [ 17 ]. The best-characterized are those associated with the quinone-binding pocket of succinate dehydrogenase (Complex II) [ 17 ]. Under aerobic conditions, Complex II acts as a dehydrogenase and converts succinate into fumarate, transferring two electrons onto UQ as the entry point into the mitochondrial electron transport chain (ETC).…”

“…UQ and RQ are highly similar in structure, but differ at Position 2 of their benzoquinone rings. UQ has a methoxy group, whereas RQ has an amine group [ 17 ]. Complex II in mitochondria with anaerobic capabilities must be able to bind both ring structures, and this difference requires a variant amino acid surrounding the quinone-binding pocket of Complex II and the related nucleotide sequence changes.…”

Identification of a novel family of benzimidazole species-selective Complex I inhibitors as potential anthelmintics

“…For example, anacardic acid is a potent inhibitor of Complex III and IV in purified mitochondria and it is unclear mechanistically how it might be acting or why it has such a strong effect on RQDM but appears to have no detectable effect on metabolism in normoxia. Other RQDM hits appear to have no effect on the ETC and must be affecting RQDM in some other unknown manner, perhaps through targeting other required components of RQDM such as AMPK 46 or on RQ synthesis itself. Thus while the mode of action of some of the RQDM hits fits with what is known of electron flow in the ETC in RQDM, others will require future studies to identify the targets and mode of action.…”