Receptor structure for F1C fimbriae of uropathogenic Escherichia coli

F1C fimbriae are correlated with uropathogenic Escherichia coli strains. Although F1C fimbriae mediate binding to kidney tubular cells, their receptor is not known. In this paper, we demonstrate for the first time specific carbohydrate residues as receptor structure for F1C-fimbria-expressing E. coli. The binding of the F1C fimbriated recombinant E. coli strain HB101(pPIL110-54) and purified F1C fimbriae to reference glycolipids of different carbohydrate compositions was evaluated by using thin-layer chromatography (TLC) overlay and solid-phase binding assays. TLC fimbrial overlay analysis revealed the binding ability of purified F1C fimbriae only to glucosylceramide (GlcCer), beta1-linked galactosylceramide 2 (GalCer2) with nonhydroxy fatty acids, lactosylceramide, globotriaosylceramide, paragloboside (nLc(4)Cer), lactotriaosylceramide, gangliotriaosylceramide (asialo-GM(2) [GgO(3)Cer]) and gangliotetraosylceramide (asialo-GM(1) [GgO(4)Cer]). The binding of purified F1C fimbriae as well as F1C fimbriated recombinant E. coli strain HB101(pPIL110-54) was optimal to microtiter plates coated with asialo-GM(2) (GgO(3)Cer). The bacterial interaction with asialo-GM(1) (GgO(4)Cer) and asialo-GM(2) (GgO(3)Cer) was strongly inhibited only by disaccharide GalNAcbeta1-4Galbeta linked to bovine serum albumin. We observed no binding to globotetraosylceramide or Forssman antigen (Gb(5)Cer) glycosphingolipids or to sialic-acid-containing gangliosides. It was demonstrated that the presence of a GalCer or GlcCer residue alone is not sufficient for optimal binding, and additional carbohydrate residues are required for high-affinity adherence. Indeed, the binding efficiency of F1C fimbriated recombinant bacteria increased by 19-fold when disaccharide sequence GalNAcbeta1-4Galbeta is linked to glucosylceramide as in asialo-GM(2) (GgO(3)Cer). Thus, it is suggested that the disaccharide sequence GalNAcbeta1-4Galbeta of asialo-GM(2) (GgO(3)Cer) which is positioned internally in asialo-GM(1) (GgO(4)Cer) is the high-affinity binding epitope for the F1C fimbriae of uropathogenic E. coli.