Mutually Exclusive Interactions of Rifabutin with Spatially Distinct Mycobacterial Cell Envelope Membrane Layers Offer Insights into Membrane-Centric Therapy of Infectious Diseases.

The mycobacterial cell envelope has spatially resolved inner and outer membrane layers with distinct compositions and membrane properties. However, the functional implication and relevance of this organization remain unknown. Using membrane biophysics and molecular simulations, we reveal a varied interaction profile of these layers with antibiotic Rifabutin, underlined by the structural and chemical makeup of the constituent lipids. The mycobacterial inner membrane displayed the highest partitioning of Rifabutin, which was located exclusively in the lipid head group/interfacial region. In contrast, the drug exhibited specific interaction sites in the head group/interfacial and hydrophobic acyl regions within the outer membrane. Altogether, we show that the design of membrane-active agents that selectively disrupt the mycobacterial outer membrane structure can increase drug uptake and enhance intracellular drug concentrations. Exploiting the mycobacterium-specific membrane-drug interaction profiles, chemotypes consisting of outer membrane-disruptive agents and antitubercular drugs can offer new opportunities for combinational tuberculosis (TB) therapy.

Biophysical characterization of mycobacterial model membranes and their interaction with rifabutin: Towards lipid-guided drug screening in tuberculosis.

Lipid structure critically dictates the molecular interactions of drugs with membranes influencing passive diffusion, drug partitioning and accumulation, thereby underpinning a lipid-composition specific interplay. Spurring selective passive drug diffusion and uptake through membranes is an obvious solution to combat growing antibiotic resistance with minimized toxicities. However, the spectrum of complex mycobacterial lipids and lack thereof of suitable membrane platforms limits the understanding of mechanisms underlying drug-membrane interactions in tuberculosis. Herein, we developed membrane scaffolds specific to mycobacterial outer membrane and demonstrate them as improvised research platforms for investigating anti-tubercular drug interactions. Combined spectroscopy and microscopy results reveal an enhanced partitioning of model drug Rifabutin in trehalose dimycolate-containing mycobacterial membrane systems. These effects are apportioned to specific changes in membrane structure, order and fluidity leading to enhanced drug interaction. These findings on the membrane biophysical consequences of drug interactions will offer valuable insights for guiding the design of more effective antibiotic drugs coupled with tuned toxicity profiles.