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

Abstract

LSECtin is a member of the C-type lectin family of glycanbinding 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 GlcNAc␤1-2Man. The inhibition constant for this disaccharide is 3.5 M, 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.

The pathogen receptor liver and lymph node sinusoidal endotelial cell C‐type lectin is expressed in human Kupffer cells and regulated by PU.1†

“…19 The removal of bacteria-derived products and microbial debris by Kupffer cells is mediated through a large array of scavenging molecules on their cell surface, and LSECtin could be an additional molecule engaged in their clearance function. The ability of LSECtin to interact with virally encoded molecules and glycoproteins with truncated complex and hybrid N-linked glycans 18 suggests its role as a scavenging molecule. Moreover, biochemical studies using recombinant LSECtin indicates its ability to specifically interact with serum proteins (data not shown).…”

“…Such a function can be inferred from a large list of pathogenic and endogenous ligands of DC-SIGN 33 and by the restricted sugar specificity of LSECtin. 18 Kupffer cells constitute more than 80% of the tissue macrophages present in the body and are the first macrophage population exposed to material derived from the gastrointestinal tract. 19 The removal of bacteria-derived products and microbial debris by Kupffer cells is mediated through a large array of scavenging molecules on their cell surface, and LSECtin could be an additional molecule engaged in their clearance function.…”

“…16,17 Although reported to be exclusively expressed on liver and lymph node sinusoidal endothelial cells, 4 LSECtin has been later found to be expressed in ex vivo isolated human peripheral blood and thymic DCs, as well as in DCs and alternatively activated macrophages generated in vitro. 5 The carbohydrate specificity of LSECtin has been recently determined, 18 and a scavenging function has been proposed because of its ability to recognize glycoproteins with truncated complex and hybrid N-linked glycans terminating in GlcNAcMan.…”

The Primed Ebolavirus Glycoprotein (19-Kilodalton GP 1,2 ): Sequence and Residues Critical for Host Cell Binding

“…Although the mucin-like domain at the C-terminal end of GP 1 can facilitate initial virus attachment to cells (1,16,18,23,25), this domain is fully dispensable for entry. Moreover, 19-kDa GP 1 clearly contains receptor binding activity, since virus binding and infection are actually enhanced after the mucin-like domain is removed (GP 1,2 ⌬) (11,21).…”

Warfare between Pathogens and Hosts: The Trickery of Sugars

“…Hepatitis C virus (HVC) and Ebola virus appear first to adhere to sinusoidal cells of the liver, eventually infecting hepatocytes. Ebola virus is also bound to LSECtin, a C-type lectin, that is present on endothelial cells of liver and lymph nodes and that prefers truncated glycans with exposed GlcNAc (11).…”