Arabinosyltransferase EmbA (EmbA)

Arabinosyltransferase EmbA is an essential enzyme in Mycobacterium tuberculosis and other mycobacteria, playing a pivotal role in the biosynthesis of the unique mycobacterial cell wall (UniProt P9WGI1). It belongs to a family of membrane-bound glycosyltransferases (EmbA, EmbB, and EmbC) that catalyze the polymerization of arabinose into the arabinan segments of arabinogalactan and lipoarabinomannan (Goude et al., 2008). EmbA and EmbB typically function as a heterodimer to synthesize the terminal hexaarabinoside motif of arabinogalactan, which provides the attachment points for mycolic acids (Amin et al., 2008). This enzyme is a well-validated therapeutic target, most notably for the first-line antitubercular drug ethambutol, which inhibits the binding of the arabinosyl donor and acceptor substrates (Zhang et al., 2020). Disruption of EmbA activity leads to a defective cell envelope, increased drug permeability, and bacteriostasis (Mikusova et al., 1995). Clinical resistance to ethambutol is frequently associated with mutations in the embCAB operon, particularly in the embB gene and the embC-embA intergenic region (Li et al., 2025). The structural characterization of the EmbA-EmbB complex has provided insights into the molecular basis of drug binding and resistance, facilitating the design of next-generation inhibitors (Zhang et al., 2020).

Other names

EmbAArabinosyltransferase AIntegral membrane indolylacetylinositol arabinosyltransferase EmbA

Ethambutol inhibits the arabinosyltransferase activity of EmbA, EmbB, and EmbC by competing with the donor substrate decaprenylphosphoryl-D-arabinose (DPA) and the acceptor substrate, thereby blocking the synthesis of the arabinan core of the mycobacterial cell wall (Zhang et al., 2020).