Human Macrophage Galactose‐Type Lectin (MGL) Recognizes the Outer Core of Escherichia coli Lipooligosaccharide

Abstract

Carbohydrate-lectin interactions intervene in and mediate most biological processes, including ac rucial modulation of immune responsest op athogens. Despite growing interesti n investigating the association between host receptorl ectins and exogenous glycanl igands, the molecular mechanisms underlying bacterial recognition by human lectins are still not fully understood.H erein, an ovel molecular interaction between the human macrophage galactose-type lectin (MGL) and the lipooligosaccharide (LOS) of Escherichia coli strain R1 is described. Saturation transfer difference NMR spectroscopy analysis, supportedb yc omputational studies, demonstrated that MGL bound to the purified deacylated LOS R1 mainly throughr ecognition of its outer core and established crucial interactions with the terminal Gala(1,2)Gal epitope. These results assess the ability of MGL to recognise glycan moieties exposed on Gram-negative bacterial surfaces.Bacterialc ell surfaces are decorated with highly diverseg lycoconjugates,i nt he form of capsular polysaccharides, peptidoglycans, lipopolysaccharides( LPSs) and other glycolipids, [1] which perform severalf unctions, ranging from structural to protective roles. [2] Bacterial glycans take part in many keyb iological events, including pathogen recognition,receptor activation, cell adhesion and signal transduction. Additionally,t hese structures often serve as molecular patterns that are recognised by specific glycan-binding receptors of the host immune system,t hus triggeringapathogen-specific immune response.It is well known that LPSs, the major constituents of the outer membrane of Gram-negative bacteria, [3] are one of the main virulence factorsofseveral feared bacterialstrains,including enteropathogenic Escherichia coli,w hich is implicated in severe foodborne and urinary tract infections. [4] From as tructural point of view,L PS is composed of three structural motifs that can be distinguishedb ecause they are encoded by different gene clusters. Lipid A, which represents the glycolipid portion, is an acylated bis-phosphorylated glucosamined isaccharide that anchors the LPS to the outer membrane. Lipid Ai sc ovalentlyl inked to ac ore oligosaccharide (OS) that can be further divided into two different portions: the more conserved inner region, which is characterised by the presence of peculiar sugar residues,s uch as 3-deoxy-d-manno-oct-2-ulopyranosonic acid (KDO),a nd the more variableo uter core. Finally,t he O-antigen, which is ap olysaccharide composed of severalO S repeating units, extends to the extracellularm edium and acts as ah ydrophilic coating surface. [3,5] However,G ram-negative bacteria can also produce rough-typeL PS, namely,l ipooligosaccharide (LOS);atruncated version of LPS that lacks the Oantigen.To date, the receptor complex formed by the toll-like receptor 4a nd the small secreted MD2 protein is among the main speciesi nvolved in bacterial LPS recognition by host immune cells. [6] More recently,i th as been shown that LPSs are also intracellularly detected by caspases...

DC/L-SIGN recognition of spike glycoprotein promotes SARS-CoV-2 trans-infection and can be inhibited by a glycomimetic antagonist

“…The extracellular domains (ECD) of DC-SIGN (residues: 66-404), L-SIGN (residues: 78-399), Langerin (residues: 68-328) and MGL (residues: 61-292) were produced and purified as already described (Achilli et al, 2020;Chabrol et al, 2012;Maalej et al, 2019;Reina et al, 2008) while SARS-CoV-2 Spike protein was expressed and purified as follows. The mammalian expression vectors used for the S ectodomain, derived from a p H vector, was a kind gift from J. McLellan (Wrapp et al, 2020).…”

Molecular Recognition in C‐Type Lectins: The Cases of DC‐SIGN, Langerin, MGL, and L‐Sectin

“…[248] In particular, STD-NMR experiments have evidenced the ability of MGL to target those LOS from E. coli R1 strains, which contain the terminal disaccharide Galα1-2Gal. [249] As suggested by the observed STD signals, the entire outer core (five residues) is involved in close contacts with the lectin surface, especially the cited disaccharide portion. The primary epitope (nonreducing Gal) is fairly similar to that of the GalNAc-containing glycosphingolipid scaffolds GM2 and asialo-GM2, suggesting that calcium coordination probably occurs in the same way.…”

The C‐type lectin receptor MGL sensesN‐acetylgalactosamine on the uniqueStaphylococcus aureusST395 wall teichoic acid

“…jejuni , N . gonorrhoeae , and Escherichia coli strain R1 (Maalej et al, ; van Sorge et al, ; van Vliet et al, ). For Escherichia coli strain R1, soluble lipo‐oligosaccharide (LOS) was identified as a ligand for recombinant human MGL, although no functional consequences were assessed (Maalej et al, ).…”