Partial Saturation of Menaquinone in : Function and Essentiality of a Novel Reductase, MenJ.

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 (designated ) encodes an enzyme which reduces the β-isoprene unit of menaquinone in , 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 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 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.