The Lipopolysaccharide from Capnocytophaga canimorsus Reveals an Unexpected Role of the Core-Oligosaccharide in MD-2 Binding

Simon Ittig,Evelina Zdorovenko,Buko Lindner,Matteo Dal Peraro,Yuriy A Knirel,Ulrich Zähringer,Marco Stenta,Pablo Manfredi,Guy R Cornelis,Stuart M Levitz

doi:10.1371/journal.ppat.1002667

Abstract

Capnocytophaga canimorsus is a usual member of dog's mouths flora that causes rare but dramatic human infections after dog bites. We determined the structure of C. canimorsus lipid A. The main features are that it is penta-acylated and composed of a “hybrid backbone” lacking the 4′ phosphate and having a 1 phosphoethanolamine (P-Etn) at 2-amino-2-deoxy-d-glucose (GlcN). C. canimorsus LPS was 100 fold less endotoxic than Escherichia coli LPS. Surprisingly, C. canimorsus lipid A was 20,000 fold less endotoxic than the C. canimorsus lipid A-core. This represents the first example in which the core-oligosaccharide dramatically increases endotoxicity of a low endotoxic lipid A. The binding to human myeloid differentiation factor 2 (MD-2) was dramatically increased upon presence of the LPS core on the lipid A, explaining the difference in endotoxicity. Interaction of MD-2, cluster of differentiation antigen 14 (CD14) or LPS-binding protein (LBP) with the negative charge in the 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) of the core might be needed to form the MD-2 – lipid A complex in case the 4′ phosphate is not present.

Highlights

Capnocytophaga canimorsus, a usual member of dog’s mouths flora [1] was discovered in 1976 [2] in patients who underwent dramatic infections after having been bitten, scratched or licked by a dog
Capnocytophaga canimorsus, a commensal bacterium in dog’s mouths, causes rare but dramatic infections in humans that have been bitten by dogs
We present here the structure of C. canimorsus lipid A, which shows several features typical for low-inflammatory lipid A

Summary

Introduction

Capnocytophaga canimorsus, a usual member of dog’s mouths flora [1] was discovered in 1976 [2] in patients who underwent dramatic infections after having been bitten, scratched or licked by a dog. C. canimorsus are able to escape complement killing and phagocytosis by human polymorphonuclear leukocytes and macrophages [7,8]. Whole bacteria are poor agonists of Toll-like receptor (TLR) 4, which results in a lack of release of proinflammatory cytokines by macrophages [9]. In addition to these ‘‘passive’’ features, C. canimorsus have been shown to harvest glycan moieties from glycoproteins at the surface of animal cells, including phagocytes [10,11,12], in addition they deglycosylate human IgG [12]

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Conclusion