A bivalent glycopeptide to target two putative carbohydrate binding sites on FimH

Abstract

FimH is a mannose-specific bacterial lectin found on type 1 fimbriae with a monovalent carbohydrate recognition domain (CRD) that is known from X-ray studies. However, binding studies with multivalent ligands have suggested an additional carbohydrate-binding site on this protein. In order to prove this hypothesis, a bivalent glycopeptide ligand with the capacity to bridge two putative carbohydrate binding sites on FimH was designed and synthesized. Anti-adhesion assays with the new bivalent ligand and type 1-fimbriated bacteria have revealed, that verification of the number of carbohydrate binding sites on FimH with a tailor-made bivalent glycopeptide requires further investigation to be conclusive.

Keywords: ELISA; FimH; bacterial adhesion; bivalent ligand; glycopeptides.

Figure 1

a) Connolly surface of FimH in complex with FimC [8]. The CRD known from X-ray structures at the tip of FimH is coloured in red and can accommodate one α-D-mannosyl residue. A second hypothetical carbohydrate binding region on the protein, as suggested by modeling studies [16], is coloured in brown and represents a more extended area on the protein. b) Docking studies were used to estimate the length of a linker that is required to bridge the putative two binding sites.

Figure 2

The bivalent glycopeptide 1 is the target molecule to test the hypothesis of two carbohydrate binding sites on FimH. Its retrosynthesis delivers the azido-functionalized mannotrioside 2 as the western part of the target structure and 2-azidoethyl mannoside 5 as its eastern portion. Squaric acid diethyl ester (DES, 4) can link both parts via two pentaglycine spacers (3).

Scheme 1

Synthesis of the eastern part of target molecule 1.

Scheme 2

Synthesis of the western part of target molecule 1.

Scheme 3

Synthesis of the target molecule 1 employing squaric acid diethylester (DES).