S78: Structural Biology of Biotin Biosynthesis

Biosynthesis of the essential co-factor- biotin, in E. coli requires the termination of the iterative fatty acid biosynthetic machinery to release the seven carbon dicarboxylic pimeloyl precursor, which is subsequently incorporated into biotin. However, it is unclear how the elongation of this fatty acid could be halted at the C7 stage. We present biochemical and structural biological evidence as to the gatekeeper enzyme that shunts pimelate from fatty acid synthetic pathway to biotin synthesis. We will also present a high-resolution co-crystal structure of an inactive variant of BioH in complex with its pimeloyl-ACP methyl ester substrate. Using the structural data as a guide, we generated several mutants that block the interaction between the two polypeptides and test the mutant phenotypes both in vitro and in vivo. Our data answers several major, long-standing questions on the biosynthesis of a primary metabolite.