Outer membrane protein size and LPS O-antigen define protective antibody targeting to the Salmonella surface

Abstract

Lipopolysaccharide (LPS) O-antigen (O-Ag) is known to limit antibody binding to surface antigens, although the relationship between antibody, O-Ag and other outer-membrane antigens is poorly understood. Here we report, immunization with the trimeric porin OmpD from Salmonella Typhimurium (STmOmpD) protects against infection. Atomistic molecular dynamics simulations indicate this is because OmpD trimers generate footprints within the O-Ag layer sufficiently sized for a single IgG Fab to access. While STmOmpD differs from its orthologue in S. Enteritidis (SEn) by a single amino-acid residue, immunization with STmOmpD confers minimal protection to SEn. This is due to the OmpD-O-Ag interplay restricting IgG binding, with the pairing of OmpD with its native O-Ag being essential for optimal protection after immunization. Thus, both the chemical and physical structure of O-Ag are key for the presentation of specific epitopes within proteinaceous surface-antigens. This enhances combinatorial antigenic diversity in Gram-negative bacteria, while reducing associated fitness costs.

Role of the lipid bilayer in outer membrane protein folding in Gram-negative bacteria

“…Measurement of water permeation in P. aeruginosa PAO1 LPS (outer)–DPPE ( di C 16:0 PE) (inner), P. aeruginosa LPS (outer)–PPPE (C 16:0 C 16:1 PE)/PVPG (C 16:0 C 18:1 PG)/CL (inner), and E. coli LPS (outer)–PPPE/PVPG/CL (inner) asymmetric bilayers by A-MD showed that the outer leaflet is relatively permeable to water when compared with the inner leaflet (with water reaching the terminal methyl groups of lipid A acyl chains) with both “rough” LPS and LPS containing an O-antigen region ( 246 , 248 , 249 , 262 ). This polarity gradient is also apparent through interactions between loop regions of OMPs and charged and polar groups on LPS that have been observed by A-MD and CG-MD ( 79 , 210 , 247 – 249 , 253 , 263 – 274 ) and specific LPS-binding sites that have been validated experimentally for trimeric porins such as OmpF ( 6 , 189 , 275 – 278 ). One area that remains understudied but warrants further investigation is the effect of the acyl tails of lipoproteins in the inner leaflet of the asymmetric OM on membrane properties.…”

“…Sam50 and Tom40) ( 22 , 23 , 74 – 77 ). Furthermore, the growth in antibiotic-resistant pathogens has highlighted the importance of the OM as a formidable barrier to the entry of antibiotics into bacteria as well as a site of efflux out ( 78 ) and as a shield against recognition of surface epitopes by natural or designed antibodies ( 79 – 82 ). Hence, insights gained from studies of OMP folding and biogenesis are also vital for our understanding of human physiology ( 83 ) and will be key in guiding our choice of targets for the generation of new antibiotics and vaccines against Gram-negative bacteria ( 84 ).…”

A general strategy to control antibody specificity against targets showing molecular and biological similarity: Salmonella case study

“…Factor (1) accounts for the fact that immunisations against different species ( S. bongori or S. enterica ), subspecies ( enterica , salamae , arizonae , diarizonae , and houtenae), and serovars (either isolated or combined in pools) expose rabbit’s immune response to antigens that differ for structure (proteins and O-lipopolysaccharides) 30 , localisation and immunodominance (e.g. outer membrane protein OmpA of Salmonella enterica serovar Typhimurium) 31 , 32 . While the α values resulting from the use of the 21 immunogens do not differ statistically after ANOVA and pairwise comparisons (Tukey, p < 0.05, Supporting Information S4 -e), Factor (1) seems to dictate the range of the α values, and thus it is the more likely player for the observed 96-fold difference.…”

Tea Tree Oil Prevents Mastitis-Associated Inflammation in Lipopolysaccharide-Stimulated Bovine Mammary Epithelial Cells

“…LPS, a macromolecular structural component on the outer membrane of gram-negative bacteria ( 14 , 15 ), can trigger an immune response in mammalian cells leading to the release of pro-inflammatory factors. Previous research underscored that the whole process of mastitis can be simulated using an LPS-induced challenge of BMEC ( 15 , 16 ). In the current study, the proliferation activity of BMEC was enhanced subsequent to LPS (50 μg/mL) challenge; however, it decreased when the concentration of LPS was >100 μg/mL, which is consistent with previous studies ( 17 ).…”