Partial Saturation of Menaquinone in <i>Mycobacterium tuberculosis</i>: Function and Essentiality of a Novel Reductase, MenJ

Abstract

Menaquinone (MK) with partially saturated isoprenyl moieties is found in a wide range of eubacteria and Archaea. In many Gram-positive organisms, including mycobacteria, it is the double bond found in the β-isoprene unit that is reduced. Mass spectral characterization of menaquinone from mycobacterial knockout strains and heterologous expression hosts demonstrates that <i>Rv0561c</i> (designated <i>menJ</i>) encodes an enzyme which reduces the β-isoprene unit of menaquinone in <i>Mycobacterium tuberculosis</i>, forming the predominant form of menaquinone found in mycobacteria. MenJ is highly conserved in mycobacteria species but is not required for growth in culture. Disruption of <i>menJ</i> reduces mycobacterial electron transport efficiency by 3-fold, but mycobacteria are able to maintain ATP levels by increasing the levels of the total menaquinone in the membrane; however, MenJ is required for <i>M. tuberculosis</i> survival in host macrophages. Thus, MK with partially hydrogenated isoprenyl moieties represents a novel virulence factor and MenJ is a contextually essential enzyme and a potential drug target in pathogenic mycobacteria and other Gram-positive pathogens.