EmbC

embC is a gene encoding the arabinosyltransferase EmbC, one of the enzymes in the embCAB operon found in many mycobacterial species, including Mycobacterium tuberculosis. The embCAB operon is involved in the biosynthesis of arabinan, a component of the cell wall arabinogalactan and lipoarabinomannan (LAM). The EmbC protein is a membrane-associated glycosyltransferase that functions together with EmbA and EmbB to transfer arabinose residues from decaprenylphosphoryl-D-arabinose (DPA) to acceptor substrates, extending arabinan chains. This activity is essential for proper cell wall assembly and integrity, influencing permeability and resistance to environmental stress.

Genetic context and expression: In many species, embC is co-transcribed with embA and embB in the embCAB operon; expression can be induced by cell wall stress and is linked to regulatory networks that govern cell envelope biosynthesis. The EmbCAB complex localizes to the cell envelope, where it participates directly in arabinan synthesis.

Clinical and research relevance: Ethambutol, a first-line anti-tuberculosis drug, inhibits the EmbCAB arabinosyltransferase complex. Mutations in embC, particularly in combination with embA or embB alterations, can contribute to reduced drug susceptibility, with embB mutations being the most common cause of ethambutol resistance. Because arabinan biosynthesis is essential for the mycobacterial cell wall, EmbC remains a focus of research as a potential target for new antimycobacterial therapies.

In summary, embC encodes a key arabinosyltransferase in mycobacteria, contributing to arabinan synthesis and cell wall integrity, and playing a role in the mechanism of ethambutol resistance.