Biosynthesis of bacterial menaquinones: the membrane-associated 1,4-dihydroxy-2-naphthoate octaprenyltransferase of Escherichia coli

Abstract

It was postulated that 1,4-dihydroxy-2-naphthoic acid is the naphthalenic intermediate in the biosynthesis of menaquinone (vitamin K2) in E. coli to which the octaprenyl side chain is attached to form demethylmenaquinone. In this work the presence of an enzyme, 1,4-dihydroxy-2-naphthoate octaprenyltransferase, which catalyzes the conversion of 1,4-dihydroxy-2-naphthoate to demethylmenaquinone was demonstrated in cell extracts of E. coli. Demethylmenaquinone-9 was formed when the naphthoate was incubated with cell extracts and the synthetic substrate, solanesyl pyrophosphate, in the presence of Triton X-100. Solanesyl monophosphate could not substitute for pyrophosphate in the reaction. The prenylation of 1,4-dihydroxy-2-naphthoate was also studied in a strain of E. coli which accumulates octaprenyl pyrophosphate, the natural precursor of the menaquinone side chain. The octaprenyltransferase was membrane bound and required Mg2+ for optimal activity. A menA- mutant of E. coli lacked octaprenyltransferase activity, suggesting that the menA gene is the structural gene for this enzyme. This strain had normal levels of 4-hydroxybenzoate octaprenyltransferase, the enzyme catalyzing the analogous prenylation reaction in ubiquinone biosynthesis, providing additional evidence that the 2 octaprenyltransferases are quite distinct.