A Novel Mechanism for LSECtin Binding to Ebola Virus Surface Glycoprotein through Truncated Glycans

Alex S Powlesland,Tanja Fisch,Maureen E Taylor,David F Smith,Bérangère Tissot,Anne Dell,Stefan Pöhlmann,Kurt Drickamer

doi:10.1074/jbc.m706292200

Abstract

LSECtin is a member of the C-type lectin family of glycan-binding receptors that is expressed on sinusoidal endothelial cells of the liver and lymph nodes. To compare the sugar and pathogen binding properties of LSECtin with those of related but more extensively characterized receptors, such as DC-SIGN, a soluble fragment of LSECtin consisting of the C-terminal carbohydrate-recognition domain has been expressed in bacteria. A biotin-tagged version of the protein was also generated and complexed with streptavidin to create tetramers. These forms of the carbohydrate-recognition domain were used to probe a glycan array and to characterize binding to oligosaccharide and glycoprotein ligands. LSECtin binds with high selectivity to glycoproteins terminating in GlcNAcbeta1-2Man. The inhibition constant for this disaccharide is 3.5 microm, making it one of the best low molecular weight ligands known for any C-type lectin. As a result of the selective binding of this disaccharide unit, the receptor recognizes glycoproteins with a truncated complex and hybrid N-linked glycans on glycoproteins. Glycan analysis of the surface glycoprotein of Ebola virus reveals the presence of such truncated glycans, explaining the ability of LSECtin to facilitate infection by Ebola virus. High mannose glycans are also present on the viral glycoprotein, which explains why DC-SIGN also binds to this virus. Thus, multiple receptors interact with surface glycoproteins of enveloped viruses that bear different types of relatively poorly processed glycans.

Highlights

Endocytosis mediated by sugar-specific receptors results in clearance of glycoproteins from circulation, so these receptors can participate in normal turnover of serum glycoproteins and in the scavenging of glycoproteins released as a result of damage to tissues [3, 4]
There are clear differences in the way that these receptors interact with viral glycoproteins, because LSECtin does not interact with lentiviral particles harboring the surface proteins of human immunodeficiency virus or hepatitis C virus, whereas DC-SIGN and DC-SIGNR do [10]
Analysis of the Ebola virus surface glycoprotein shows the presence of both this target structure and high mannose oligosaccharides, which would account for the ability of LSECtin as well as DC-SIGN and DC-SIGNR to bind to the viral glycoprotein

Summary

Introduction

Endocytosis mediated by sugar-specific receptors results in clearance of glycoproteins from circulation, so these receptors can participate in normal turnover of serum glycoproteins and in the scavenging of glycoproteins released as a result of damage to tissues [3, 4]. It is demonstrated that the most effective glycan ligands for LSECtin contain the disaccharide sequence GlcNAc␤1–2Man. Analysis of the Ebola virus surface glycoprotein shows the presence of both this target structure and high mannose oligosaccharides, which would account for the ability of LSECtin as well as DC-SIGN and DC-SIGNR to bind to the viral glycoprotein.

Results

Conclusion