InterPro domain: IPR010198

This entry represents an enzyme, naphthoate synthase 4.1.3.36 , MenB or dihydroxynaphthoic acid synthetase, which is involved in the fifth step of the menaquinone biosynthesis pathway. Menaquinone (vitamin K2), is an essential quinone used in electron-transfer pathways serving as the major electron carrier during anaerobic growth. In the bacterium, the biosynthetic pathway in bacteria typically comprises 6-7 steps [ 1 ]. Together with o-succinylbenzoate-CoA ligase (menE IPR010192 ),MenB takes 2-succinylbenzoate and converts it into 1,4-di-hydroxy-2-naphthoic acid (DHNA) [ 2 , 2 , 3 , 4 ]. The conversion of o-succinylbenzoate-CoA ligase to DHNA is mediated by the enzyme DHNA synthase, which is encoded by menB [ 5 ].

The protein structure of naphthoate synthase has been expressed in Escherichia coli, purified and crystallized, and found to have fold characteristics of the crotonase family of enzymes, which is notable for the presence of several highly flexible regions around the active site. The C-terminal region of the protein may play a critical role both in completion of the binding pocket and in stabilisation of the hexamer, suggesting a link between oligomerisation and catalytic activity [ 6 ].

1. Biosynthesis of menaquinone (vitamin K2) and ubiquinone (coenzyme Q): a perspective on enzymatic mechanisms. Vitam. Horm. 61, 173-218
2. Crystal structure of Mycobacterium tuberculosis MenB, a key enzyme in vitamin K2 biosynthesis. J. Biol. Chem. 278, 42352-60
3. Menaquinone (vitamin K2) biosynthesis: conversion of o-succinylbenzoic acid to 1,4-dihydroxy-2-naphthoic acid by Mycobacterium phlei enzymes. J. Bacteriol. 140, 92-8
4. Identification of Bacillus subtilis men mutants which lack O-succinylbenzoyl-coenzyme A synthetase and dihydroxynaphthoate synthase. J. Bacteriol. 145, 328-32
5. Menaquinone (vitamin K2) biosynthesis: nucleotide sequence and expression of the menB gene from Escherichia coli. J. Bacteriol. 174, 5057-62
6. Structure of naphthoate synthase (MenB) from Mycobacterium tuberculosis in both native and product-bound forms. Acta Crystallogr. D Biol. Crystallogr. 61, 1199-206