Poster Presentation The 46th Lorne Conference on Protein Structure and Function 2021

Understanding the molecular recognition of Bacteroides fragilis glycosphingolipids by Natural killer T-cell receptor (#315)

Praveena Thirunavukkarasu 1 , Sungwhan F. Oh 2 3 , Hee Bum Song 4 , Shankar Iyer 5 , Ji-Sun Yoo 3 , Changwon C. Lee 2 , Da-Jung Jung 3 , Jérôme Le Nours 1 , Hyunsoo Kim 4 , Yoon Soo Hwang 4 , Ledia Gebremedhin 3 , Deniz Erturk-Hasdemir 2 , Richard S. Blumberg 5 , Seung Bum Park 4 , Dennis L. Kasper 2 , Jamie Rossjohn 1 6 7
  1. Infection and Immunity program, Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Melbourne, Victoria, Australia
  2. Department of Immunology, Blavatnik Institute of Harvard Medical school, Boston, USA
  3. Center for Experimental Therapeutics and Reperfusion injury, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Boston, USA
  4. CRI center for Chemical Proteomics, Department of Chemistry, Seoul National University, Seoul, Republic of Korea
  5. Division of Gastroenterology, Hepatology and Endoscopy, Department of Medicine, Brigham and Women’s Hospital, Boston, USA
  6. Institute of Infection and Immunity, Cardiff University, Heath Park, Cardiff, UK
  7. Australian Research Council Centre of Excellence for Advanced Molecular Imaging, Monash University, Australia, Melbourne, Victoria, Australia

The human gut microbiota is composed of more than 50% of Bacteroides species whose membranes are enriched in sphingolipids. In particular, Bacteroides fragilis produced glycosphingolipids termed as α-Galactosylceramides (α-GalCerBf) have the ability to activate both mouse and human type I Natural Killer T (NKT) cells. While they share key chemical similarities with the type I NKT cell marker antigen, α-Galactosylceramide (KRN7000), they possess distinctive structural features including short branched acyl chains with the variations in their hydroxyl group positions. Here, using X-ray crystallography, we have determined the crystal structures of four type I NKT TCR-mouse CD1d-lipid ternary complexes revealing a parallel docking mode of the TCR atop the F’-pocket of the antigen presenting molecule CD1d in recognising the presented bacterial sphingolipids. The measured binding affinities between the mouse CD1d presented sphingolipids and NKT TCR were observed to be in nanomolar range. As translation of results from benchside to bedside with KRN7000 has proven challenging, the study of these physiologically relevant α-GalCerBf lipids may open new avenues in designing novel immunomodulatory agents to achieve desired immune outcomes in various clinical conditions. Further, this study sheds light on the better understanding of the existing symbiotic relationship between the microbes producing these endogenous lipids and the host. This manuscript is currently under review in Cell journal.