The first step in the infection of humans by microbial pathogens is their adherence to host tissue cells, which is frequently based on the binding of carbohydrate-binding proteins (lectin-like adhesins) to human cell receptors that expose glycans. In only a few cases have the human receptors of pathogenic adhesins been described. A novel strategy—based on the construction of a lectin-glycan interaction (LGI) network—to identify the potential human binding receptors for pathogenic adhesins with lectin activity was developed. The new approach is based on linking glycan array screening results of these adhesins to a human glycoprotein database via the construction of an LGI network. This strategy was used to detect human receptors for virulent Escherichia coli (FimH adhesin), and the fungal pathogens Candida albicans (Als1p and Als3p adhesins) and C. glabrata (Epa1, Epa6, and Epa7 adhesins), which cause candidiasis. This LGI network strategy allows the profiling of potential adhesin binding receptors in the host with prioritization, based on experimental binding data, of the most relevant interactions. New potential targets for the selected adhesins were predicted and experimentally confirmed. This methodology was also used to predict lectin interactions with envelope glycoproteins of human-pathogenic viruses. It was shown that this strategy was successful in revealing that the FimH adhesin has anti-HIV activity.
SummaryThe opportunistic pathogen Candida albicans expresses on its surface Als (Agglutinin like sequence) proteins, which play an important role in the adhesion to host cells and in the development of candidiasis. The binding specificity of these proteins is broad, as they can bind to various mammalian proteins, such as extracellular matrix proteins, and N-and E-cadherins. The N-terminal part of Als proteins constitutes the substrate-specific binding domain and is responsible for attachment to epithelial and endothelial cells. We have used glycan array screening to identify possible glycan receptors for the binding domain of Als1p-N. Under those conditions, Als1p-N binds specifically to fucose-containing glycans, which adds a lectin function to the functional diversity of the Als1 protein. The binding between Als1p-N and BSAfucose glycoconjugate was quantitatively characterized using surface plasmon resonance, which demonstrated a weak millimolar affinity between Als1p-N and fucose. Furthermore, we have also quantified the affinity of Als1p-N to the extracellular matrix proteins proteins fibronectin and laminin, which is situated in the micromolar range. Surface plasmon resonance characterization of Als1p-N-Als1p-N interaction was in the micromolar affinity range.
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