EmbCAB arabinosyltransferase (EmbCAB)

The EmbCAB arabinosyltransferases are a complex of membrane-bound enzymes (EmbA, EmbB, and EmbC) essential for the synthesis of the mycobacterial cell wall in species such as Mycobacterium tuberculosis (UniProt P9WNK3, P9WNK5, P9WNK1) [1]. These enzymes catalyze the transfer of arabinose residues from the donor molecule decaprenyl-phospho-arabinose (DPA) to the growing arabinan chains of arabinogalactan and lipoarabinomannan [2]. Specifically, EmbA and EmbB are primarily involved in the formation of the arabinan core of arabinogalactan, while EmbC is responsible for the synthesis of the arabinan component of lipoarabinomannan [2]. Because these glycans are critical for the structural integrity and virulence of the mycobacterium, the EmbCAB complex is a validated therapeutic target [3]. The first-line antitubercular drug ethambutol exerts its antibacterial effect by inhibiting these enzymes, leading to a weakened cell wall and increased susceptibility to other agents (DrugBank DB00330) [4]. Recent cryo-electron microscopy studies have revealed that ethambutol binds within the active sites of EmbB and EmbC, directly obstructing the binding of the DPA substrate [2]. Mutations in the genes encoding these proteins, particularly the embB gene at codon 306, are the primary mechanism by which clinical resistance to ethambutol arises [5]. Understanding the structural biology of the EmbCAB complex is crucial for developing next-generation inhibitors that can overcome existing resistance mechanisms in multi-drug resistant tuberculosis strains.

Other names

Arabinosyltransferase AArabinosyltransferase BArabinosyltransferase CEmbAEmbBEmbCEthambutol-sensitive arabinosyltransferase

Ethambutol acts as a competitive inhibitor of the EmbCAB enzymes by mimicking the substrate decaprenyl-phospho-arabinose (DPA), thereby blocking the polymerization of arabinose into the mycobacterial cell wall [2, 4].