Fimbriae are proteinogeneous appendages on the surface of bacteria, which mediate bacterial adhesion to the host cell glycocalyx. The so-called type 1 fimbriae exhibit specificity for alpha-d-mannosides and, therefore, they are assumed to mediate bacterial adhesion via the interaction of a fimbrial lectin and alpha-d-mannosyl residues exposed on the host cell surface. This carbohydrate-specific adhesive protein subunit of type 1 fimbriae has been identified as a protein called FimH. The crystal structure of this lectin is known and, based on this information, the molecular details of the interaction of mannoside ligands and FimH are addressed in this paper. Computer-based docking methods were used to evaluate known ligands as well as to design new ones. Then, a series of new mannosides with extended aglycon was synthesized and tested as inhibitors of type 1 fimbriae-mediated bacterial adhesion in an ELISA. The results obtained were compared to the predictions and findings as delivered by molecular modeling. This study led to an improved understanding of the ligand-receptor interactions under investigation.

The glycocalyx of eukaryotic cells is composed of glycoconjugates, which carry highly complex oligosaccharide portions. To elucidate the biological role and function of the glycocalyx in cell-cell communication and cellular adhesion processes, glycomimetics have become targets of glycosciences, which resemble the composition and structural complexity of the glycocalyx constituents. Here, we report about the synthesis of a class of oligosaccharide mimetics of a high-mannose type, which were obtained by mannosylation of spacered mono- and oligosaccharide cores. These carbohydrate-centered cluster mannosides have been targeted as inhibitors of mannose-specific bacterial adhesion, which is mediated by so-called type 1 fimbriae. Their inhibitory potencies were measured by ELISA and compared to methyl mannoside as well as to a series of mannobiosides, and finally to the polysaccharide mannan. The obtained results suggest a new interpretation of the mechanisms of bacterial adhesion according to a macromolecular rather than a multivalency effect.

SummaryFimH 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.

A Al ll l e en nq qu ui ir ri ie es s a an nd d m ma an nu us sc cr ri ip pt ts s s sh ho ou ul ld d b be e d di ir re ec ct te ed d t to o: : Volume 55, 2002 © CSIRO 2002 publishing research papers from all fields of chemical science, including synthesis, structure, new materials, macromolecules, supramolecular chemistry, biological chemistry, nanotechnology, surface chemistry, and analytical techniques.Mannose-specific adhesion of E. coli bacteria to their host cells is mediated by so-called type 1 fimbriae containing lectin domains present on the type 1 fimbrial FimH protein. The crystal structure of a FimH-FimC(chaperone) protein complex revealed a number of amino acids in the carbohydrate binding site with aromatic side chains. This finding is in keeping with earlier results showing high inhibitory potencies of aryl mannosides when tested as inhibitors of type 1 fimbriae-mediated bacterial adhesion. In addition, clustering of mannosyl moieties also led to favourable effects, as in the case of trivalent cluster mannosides such as (1). In order to combine both, i.e. the clustering approach and the advantage of an aromatic moiety, the herein presented study has emphasized the synthesis of three cluster mannosides (2), (3), and (4), as ligands for the type 1 fimbrial lectin, which contain a phenyl partial structure in different proximity to the core of the molecule. The inhibitory potencies of the new cluster mannosides were determined in enzyme-linked immunosorbent assays (ELISAs). C H 0 2 0 2 5 T r i v a l e n t C l u s t e r Ma n n o s i d e s w i t h A r o m a t i c P a r t i a l S t r u c t u r e N . R ö c k e n d o r f , O . S p e r l i n g a n d T . K . L i n d h o r s t N . R ö c k e n d o r f , O . S p e r l i n g a n d T . K. L i n d h o r s t

Non-covalent interactions between structural parts of complex oligosaccharides and saccharide-recognising proteins are of crucial importance for many cell communication phenomena. Specificity of such interactions and stability of these ligand-receptor complexes are achieved through multivalent interactions between multiple copies of a saccharide ligand and a corresponding number of protein receptors. Substances presenting multiple copies of the saccharide ligand on easily accessible scaffold molecules therefore appear to be promising tools for study of multivalent interactions and their possible inhibition. Such multivalent glycomimetics can be prepared by attachment of saccharide residues to the surface functional groups of dendrimers. In the course of our work, we have prepared novel glycodendrimers with gly-