Modeling Diversity in Structures of Bacterial Outer Membrane Lipids

Lipopolysaccharides (LPSs) are vital components of the outer membrane of Gram-negative bacteria, and they act as extremely strong stimulators of innate immunity in diverse eukaryotic species. The primary immunostimulatory center of the LPS molecule is lipid A, a disaccharide-bound lipophilic domain. Considering the broad diversity in bacterial species, there are variations in the lipid A structures and their immunogenic potencies. In this work, we model the lipid A structures of eight commensal or human pathogenic bacterial species: Helicobacter pylori, Porphyromonas gingivalis, Bacteroides fragilis, Bordetella pertussis, Chlamydia trachomatis, Campylobacter jejuni, Neisseria meningitidis, and Salmonella Minnesota. The membrane properties of these bacterial species were characterized and compared using molecular simulations. The structure-property relationships that emerge from this lipid A molecular library highlight the roles of acyl chain lengths, number of chains, phosphorylation state, membrane composition, and counterion charge in regulating the phase transition temperature of the membrane, diffusion coefficient of the lipids, and membrane thickness. The molecular and structural insights provided reveal the diversity in bacterial outer membrane lipids and their contribution to human disease and immunity.