Protein-bound molybdenum cofactor is bioavailable and rescues molybdenum cofactor-deficient C. elegans

Abstract

The molybdenum cofactor (Moco) is a 520 dalton prosthetic group that is synthesized in a multi-step enzymatic pathway present in most Archaea, Bacteria, and Eukarya. In animals, four oxidases (among them sulfite oxidase) use Moco as a prosthetic group. Moco is essential in animals; humans with mutations in genes that encode Moco-biosynthetic enzymes display lethal neurological and developmental defects. Moco supplementation seems a logical therapy, however the instability of Moco has precluded biochemical and cell biological studies of Moco transport and bioavailability. The nematode Caenorhabditis elegans can take up Moco from its bacterial diet and transport it to cells and tissues that express Moco-requiring enzymes, suggesting a system for Moco uptake and distribution. Here we show that protein-bound Moco is the stable, bioavailable species of Moco taken up by C. elegans from its diet and is an effective dietary supplement in a C. elegans model of Moco deficiency. Diverse purified Moco:protein complexes from bacteria, bread mold, green algae, and dairy cows were able to support the growth of otherwise Moco-deficient C. elegans mutants grown on Moco-deficient E. coli. We show that these Moco:protein complexes are very stable, suggesting they may provide a strategy for the production and delivery of therapeutically active Moco to treat human Moco deficiency.

Dietary molybdenum cofactor promotes fitness by increasing Moco content and sulfite oxidase activity in the nematode C. elegans

“…To expand our understanding of Moco homeostasis, we produced C. elegans extracts from animals lacking either endogenous Moco synthesis or dietary Moco. These extracts were used to quantify Moco content and SUOX-1 activity, providing biochemical clarity to our genetic system (12)(13)(14). We found that C. elegans mutants lacking endogenous Moco biosynthesis displayed reduced Moco content and SUOX-1 activity.…”

“…Growth assays were performed as previously described with minor modifications (13,14). Briefly, wild-type and mutant C. elegans were synchronized at the first stage of larval development (L1) and subsequently cultured on NGM seeded with wild-type or mutant E. coli for 72 hours at 20°C.…”

“…Thus, it seems likely that Moco biology uncovered in the nematode C. elegans will be found throughout the tree of life. Our discovery that dietary Moco promotes Moco content, SUOX-1 activity, and rescues C. elegans Moco deficiency lays additional intellectual groundwork for developing Moco supplementation as a therapy to treat human Moco deficiency (13,14). However, uptake of exogenous Moco has yet to be examined or observed in another organism.…”

“…moc mutant animals are viable because C. elegans stably acquires mature Moco from its bacterial diet. This dietary Moco is stabilized by Moco-binding/using proteins and is transported by unknown mechanisms throughout the C. elegans animal to support the activity of its Moco-requiring enzymes (13). Unsurprisingly, Moco is essential for C. elegans viability: animals lacking both endogenous Moco synthesis and dietary Moco arrest larval development and die.…”

“…Most Moco-requiring cells are believed to synthesize Moco de novo. However, recent advances in the nematode Caenorhabditis elegans have demonstrated that Moco can move not only between cells and tissues but between disparate organisms (12)(13)(14). Unlike other animals studied, C. elegans with null mutations in genes encoding the Moco-biosynthetic enzymes are viable and fertile.…”