Mycobacterium tuberculosis antigen 85 complex (Ag85 complex)

The **Mycobacterium tuberculosis antigen 85 complex** (commonly known as the Ag85 complex) is a major secreted protein family composed of three homologous enzymes: Ag85A, Ag85B, and Ag85C[2][3]. These mycolyltransferases are essential for the final steps in *M. tuberculosis* cell wall biogenesis, where they catalyze the transfer of mycolic acids to create trehalose dimycolate and other glycolipids critical for cell envelope integrity[1][2][3][4]. As secreted and highly immunogenic proteins, members of the Ag85 complex are involved in pathogenesis, immune evasion, and intracellular survival of the bacterium[4][5]. They are robustly recognized by the host immune system, making them important antigens for tuberculosis vaccines, diagnostic assays, and therapeutic drug development[3][6][8]. The crystal structures show an alpha/beta-hydrolase fold with a conserved active site suitable for small-molecule inhibition[2]. The Ag85 complex is a promising multi-faceted target due to its essentiality, accessibility, limited redundancy, and unique enzymatic activity not present in humans[1][2][3]. Drugs such as ebselen target and inactivate these enzymes, suggesting a path toward novel multi-drug resistant TB therapies[1].

Other names

Antigen 85 complexAg85AAg85BAg85CMycolyltransferase complexFibronectin-binding protein complex

Inhibitors bind to the active site of antigen 85 proteins, block mycolyltransferase catalytic activity, and disrupt cell wall synthesis[1][2]. Drugs such as ebselen covalently modify key active site residues (e.g., Cys209 in Ag85C), leading to inactivation of the enzyme and impairment of mycolic acid transfer[1].