Exploring the stereochemistry-specific tendency for interdigitation in synthetic monomycoloyl glycerol analogs through molecular dynamics simulations

Synthetic monomycoloyl glycerol (MMG) analogs possess robust immunostimulatory activity and are investigated as adjuvants for subunit vaccines in preclinical and clinical studies. These synthetic lipids consist of a glycerol moiety attached to a corynomycolic acid. Previous experimental studies have shown that the stereochemistry of the lipid acid moiety affects whether the MMG analogs self-assemble into interdigitated or non-interdigitated structures below the main phase transition temperature (Tm). In this study, we elucidated possible thermodynamic mechanisms governing the phase behavior of MMG analogs by exploring their conformations, interactions, and dynamics using molecular dynamics (MD) simulations. We compared two analogs, MMG-1 and MMG-6, which differ only by the stereochemistry of the lipid acid moiety; the former has a configuration different from the natural MMG, and the latter displays a native-like stereochemistry. Three different membrane states were simulated: 1) a non-interdigitated single bilayer, 2) a non-interdigitated double bilayer, and 3) a fully interdigitated double bilayer. Our results indicate that the propensity for interdigitation of the MMG analogs is linked to the degree to which their hydrocarbon chains are ordered and oriented, and the extent of the intermolecular interactions in their hydrophilic region. This study demonstrates how MD simulations can enhance the molecular understanding of vaccine adjuvants.