Oleic Acid Metabolism via a Conserved Cytochrome P450 System-Mediated ω-Hydroxylation in the Bark Beetle-Associated Fungus Grosmannia clavigera

The bark beetle-associated fungus Grosmannia clavigera participates in the large-scale destruction of pine forests. In the tree, it must tolerate saturating levels of toxic conifer defense chemicals (e.g. monoterpenes). The fungus can metabolize some of these compounds through the ß-oxidation pathway and use them as a source of carbon. It also uses carbon from pine triglycerides, where oleic acid is the most common fatty acid. High levels of free fatty acids, however, are toxic and can cause additional stress during host colonization. Fatty acids induce expression of neighboring genes encoding a cytochrome P450 (CYP630B18) and its redox partner, cytochrome P450 reductase (CPR2). The aim of this work was to study the function of this novel P450 system. Using LC/MS, we biochemically characterized CYP630 as a highly specific oleic acid ω-hydroxylase. We explain oleic acid specificity using protein interaction modeling. Our results underscore the importance of ω-oxidation when the main ß-oxidation pathway may be overwhelmed by other substrates such as host terpenoid compounds. Because this CYP-CPR gene cluster is evolutionarily conserved, our work has implications for metabolism studies in other fungi.