Protein complex supports bacterial envelope and TB drug resistance

Tuberculosis remains difficult to treat because Mycobacterium tuberculosis (Mtb) has a complex, impermeable cell envelope that gives the bacterium intrinsic drug resistance. To understand how that barrier is built and maintained, researchers led by Sabine Ehrt looked for proteins that keep the envelope intact and help Mtb withstand antibiotics. They identified a periplasmic protein complex made up of FecB and Rv3035. The team found that FecB interacts with Rv3035 to form a stable heterodimer, and that this heterodimer associates with AftB, a cell envelope biosynthesis protein. By solving structures of Rv3035 by itself and in complex with FecB, the researchers mapped physical contacts and pinpointed critical residues needed for the proteins to come together and function. These findings show that a previously unrecognized assembly of periplasmic proteins plays a direct role in maintaining the envelope that contributes to Mtb’s built-in resistance to multiple drugs.

The study combined structural biology, genetic interaction studies and functional assays to connect protein structure with bacterial physiology. Structural analysis produced models of Rv3035 alone and bound to FecB, and identified specific residues required for complex formation and function. Genetic approaches, including co-essentiality and genetic interaction analyses, revealed a functional link between FecB, Rv3035 and AftB. AftB is an arabinofuranosyltransferase responsible for synthesizing key envelope components, arabinogalactan and lipoarabinomannan. Loss of either FecB or Rv3035 disrupted AftB-mediated arabinan synthesis, indicating that the FecB–Rv3035 complex supports AftB’s enzymatic activity. The physiological importance of these interactions was shown in animal experiments: FecB is required for Mtb virulence in mice. Taken together, the structural and genetic results tie molecular interactions to changes in cell envelope construction and to the bacterium’s ability to cause disease.

These results matter because they point to specific components that keep Mtb’s protective envelope intact and thus contribute to intrinsic multidrug resistance. By showing that FecB and Rv3035 form a periplasmic complex that supports the arabinofuranosyltransferase AftB and that loss of these proteins impairs arabinan synthesis and virulence, the research highlights FecB, Rv3035 and AftB as promising therapeutic targets. Targeting this complex could weaken the envelope, potentially making Mtb more vulnerable to existing drugs and to host defenses. The direct structural information and the identification of critical residues also provide starting points for designing molecules that disrupt the complex and interfere with envelope biosynthesis, offering a focused route for future drug discovery aimed at overcoming intrinsic drug resistance.