Bypass of the canonical biotin synthesis pathway in yeast

Biotin serves as an essential cofactor for several carboxylation enzymes that catalyze reactions vital for cell survival and proliferation. While bacterial biotin synthesis pathways are well characterized, the mechanisms in eukaryotic organisms remain poorly understood. In Saccharomyces cerevisiae, Bio1 catalyzes the initial and rate-limiting step in the yeast biosynthetic pathway. Previous workers demonstrated that the Bio1 ortholog from the related yeast, Cyberlindnera fabianii, functionally substituted for S. cerevisiae Bio1 and greatly increased growth in the absence of biotin. However, we show this enzyme has far more remarkable capabilities. Through combined in vivo and in vitro experiments, we report that C. fabianii Bio1 (CfBio1) is a 2-oxoglutarate-dependent nonheme iron (II) dioxygenase. The enzyme utilizes the free fatty acid, oleic acid (C18:1^Δ9), as substrate, a departure from all previously characterized biotin pathways. Our study shows that CfBio1 catalyzes multiple rounds of oxidation and produces a nine-carbon intermediate, 7-oxononanoate, as opposed to the conventional seven-carbon initial intermediate, pimelate. Moreover, CfBio1 effectively replaces the well-studied Escherichia coli BioC-BioH enzymes that initiate biotin synthesis and remarkably, also bypasses BioF, the second enzymatic step in the pathway. The enzyme bypasses the first two steps of the canonical biotin synthesis pathway both in vivo and in vitro.