Structural insight in histo‐blood group binding by the F18 fimbrial adhesin FedF

Abstract

SummaryF18-positive enterotoxigenic and Shiga toxinproducing Escherichia coli are responsible for postweaning diarrhoea and oedema disease in pigs and lead to severe production losses in the farming industry. F18 fimbriae attach to the small intestine of young piglets by latching onto glycosphingolipids with A/H blood group determinants on type 1 core. We demonstrate the N-terminal domain of the F18 fimbrial subunit FedF to be responsible for ABH-mediated attachment and present its X-ray structure in ligandfree form and bound to A and B type 1 hexaoses. The FedF lectin domain comprises a 10-stranded immunoglobulin-like b-sandwich. Three linear motives, Q 47-N50, H88-S90 and R117-T119, form a shallow glycan binding pocket near the tip of the domain that is selective for type 1 core glycans in extended conformation. In addition to the glycan binding pocket, a polybasic loop on the membrane proximal surface of FedF lectin domain is shown to be required for binding to piglet enterocytes. Although dispensable for ABH glycan recognition, the polybasic surface adds binding affinity in the context of the host cell membrane, a mechanism that is proposed to direct ABH-glycan binding to cell-bound glycosphingolipids and could allow bacteria to avoid clearance by secreted glycoproteins.

Enterotoxigenic Escherichia coli strains are highly prevalent in Ugandan piggeries but disease outbreaks are masked by antibiotic prophylaxis

“…Variability at amino acid positions 47 and 73 differentiated the two variants with a lysine (F18ac) to glutamine (F18ab) substitution at position 47 and a glycine (F18ac) to aspartic acid or asparagine (F18ab) substitution at position 73. We mapped the sequence variation of fedF onto the recently elucidated structure of the co-complex between FedF and the blood group A type 1 hexasaccharide (Moonens et al 2012). Interestingly, residue 47 and 90 of FedF, which interact with the carbohydrate ligand, varied between the different isolates (Fig.…”

“…Amino acid residues 47 and 90 are varying between clinical isolates and are involved in receptor recognition. Lower panel (b): structure of the co-complex between FedF and blood group A type 1 hexasaccharide (adapted from Moonens et al 2012). Interacting residues and the monosaccharides constituents of the ligand are named…”

Structural and Functional Insight into the Carbohydrate Receptor Binding of F4 Fimbriae-producing Enterotoxigenic Escherichia coli

“…The involvement of a hydrophobic interaction with an aromatic side chain is a common theme in ligand recognition by fimbrial adhesins. FimH, PsaA, and FedF also make use of a tyrosine residue in their binding pocket to interact with mannose, galactose, and fucose residues, respectively (48,51,52). PapG and F17-G employ the hydrophobic interaction of a tryptophan side chain against the carbon atoms of the sugar (47,49).…”

“…A recurrent theme in the interaction of chaperone/usher-pili with host tissue manifests there is more than meets the eye. The F18 fimbrial adhesin FedF features a coincidence binding mechanism that targets FedF to glycosphingolipid receptors embedded in the cellular membrane (48). Type 1 pili and Cfa/I employ shear-enhanced adhesion to withstand the hydrodynamic forces acting on biological surfaces and direct binding to surface-bound receptors rather than toward soluble but otherwise identical receptors or soluble inhibitors (53, 59 -61).…”

Duality of β-glucan microparticles: antigen carrier and immunostimulants

“…The FedF subunit of F18 fimbriae is located in a dedicated single-copy adhesin at the distal tip of the fimbriae. 26 Tipadhesins are usually composed of two immunoglobulin (Ig)-like domains: an N-terminal lectin or receptor binding module and a C-terminal pilin. As it needs a complementary β-strand from the FedE subunit, using donor strand complementation is necessary to achieve a stable recombinant expression of FedF.…”