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Published on: November 5, 2019
Identification of a novel cationic glycolipid in Streptococcus agalactiae that contributes to brain entry and
Luke R Joyce1,2, Haider S Manzer2, Jéssica da C Mendonça2,3
1Department of Biological Sciences, The University of Texas at Dallas, Richardson, Texas, United States of America.
Abstract:
Bacterial membrane lipids are critical for membrane bilayer formation, cell division, protein localization, stress responses, and pathogenesis. Despite their critical roles, membrane lipids have not been fully elucidated for many pathogens. Here, we report the discovery of a novel cationic glycolipid, lysyl-glucosyl-diacylglycerol (Lys-Glc-DAG), which is synthesized in high abundance by the bacterium Streptococcus agalactiae (Group B Streptococcus, GBS). To our knowledge, Lys-Glc-DAG is more positively charged than any other known lipids. Lys-Glc-DAG carries 2 positive net charges per molecule, distinct from the widely described lysylated phospholipid lysyl-phosphatidylglycerol (Lys-PG) that carries one positive net charge due to the presence of a negatively charged phosphate moiety. We use normal phase liquid chromatography (NPLC) coupled with electrospray ionization (ESI) high-resolution tandem mass spectrometry (HRMS/MS) and genetic approaches to determine that Lys-Glc-DAG is synthesized by the enzyme MprF in GBS, which covalently modifies the neutral glycolipid Glc-DAG with the cationic amino acid lysine. GBS is a leading cause of neonatal meningitis, which requires traversal of the endothelial blood-brain barrier (BBB). We demonstrate that GBS strains lacking mprF exhibit a significant decrease in the ability to invade BBB endothelial cells. Further, mice challenged with a GBSΔmprF mutant developed bacteremia comparably to wild-type (WT) infected mice yet had less recovered bacteria from brain tissue and a lower incidence of meningitis. Thus, our data suggest that Lys-Glc-DAG may contribute to bacterial uptake into host cells and disease progression. Importantly, our discovery provides a platform for further study of cationic lipids at the host-pathogen interface.
Insights
Researchers discovered a novel cationic lipid, lysyl-glucosyl-diacylglycerol (Lys-Glc-DAG), in Group B Streptococcus. This lipid aids bacterial invasion of the blood-brain barrier, potentially contributing to meningitis.
Area of Science:
- Microbiology
- Lipid Biochemistry
- Pathogenesis
Background:
- Bacterial membrane lipids are crucial for various cellular functions and pathogen survival.
- The lipid composition of many pathogens, including Streptococcus agalactiae (GBS), remains incompletely understood.
- Understanding these lipids is vital for developing new therapeutic strategies against bacterial infections.
Purpose of the Study:
- To identify and characterize novel membrane lipids in Streptococcus agalactiae (GBS).
- To investigate the role of a newly discovered cationic glycolipid, lysyl-glucosyl-diacylglycerol (Lys-Glc-DAG), in GBS pathogenesis.
- To explore the potential contribution of Lys-Glc-DAG to GBS invasion of the blood-brain barrier (BBB).
Main Methods:
- Normal phase liquid chromatography (NPLC) coupled with electrospray ionization (ESI) high-resolution tandem mass spectrometry (HRMS/MS) for lipid identification.
- Genetic approaches, including the creation of GBS mutants lacking the mprF gene.
- In vitro assays to assess the invasion of BBB endothelial cells by GBS strains.
- In vivo mouse models to evaluate the impact of GBS mutants on bacteremia, brain colonization, and meningitis incidence.
Main Results:
- Discovery of a novel, highly cationic glycolipid, lysyl-glucosyl-diacylglycerol (Lys-Glc-DAG), synthesized by GBS.
- Lys-Glc-DAG is produced by the enzyme MprF, which modifies glucosyl-diacylglycerol (Glc-DAG) with lysine.
- GBS strains deficient in mprF showed significantly reduced ability to invade BBB endothelial cells.
- Mice infected with a GBSΔmprF mutant exhibited reduced bacterial load in the brain and lower rates of meningitis compared to wild-type.
Conclusions:
- Lysyl-glucosyl-diacylglycerol (Lys-Glc-DAG) is a novel cationic lipid synthesized by Streptococcus agalactiae.
- The MprF enzyme is responsible for Lys-Glc-DAG synthesis and plays a role in GBS invasion of the blood-brain barrier.
- Lys-Glc-DAG may facilitate bacterial entry into host cells and contribute to the pathogenesis of GBS meningitis.
- This discovery opens new avenues for understanding cationic lipids in host-pathogen interactions and developing targeted therapies.
