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The Aspergillus fumigatus lectin AFL was recently described as a new member of the AAL lectin family. As a lectin from an opportunistic pathogen, it might play an important role in the interaction of the pathogen with the human host. A detailed study of structures of AFL complexed with several monosaccharides and oligosaccharides, including blood-group epitopes, was combined with affinity data from SPR and discussed in the context of previous findings. Its six binding sites are non-equivalent, and owing to minor differences in amino-acid composition they exhibit a marked difference in specific ligand recognition. AFL displays a high affinity in the micromolar range towards oligosaccharides which were detected in plants and also those bound on the human epithelia. All of these results indicate AFL to be a complex member of the lectin family and a challenging target for future medical research and, owing to its binding properties, a potentially useful tool in specific biotechnological applications.

Double-stranded regions of the telomeres are recognized by proteins containing Myb-like domains conferring specificity toward telomeric repeats. Although biochemical and structural studies revealed basic molecular principles involved in DNA binding, relatively little is known about evolutionary pathways leading to various types of Myb domain-containing proteins in divergent species of eukaryotes. Recently we identified a novel type of telomere-binding protein YlTay1p from the yeast Yarrowia lipolytica containing two Myb domains (Myb1, Myb2) very similar to the Myb domain of mammalian TRF1 and TRF2. In this study we prepared mutant versions of YlTay1p lacking Myb1, Myb2, or both Myb domains and found that YlTay1p carrying either Myb domain exhibits preferential affinity to both Y. lipolytica (GGGTTAGTCA)(n) and human (TTAGGG)(n) telomeric sequences. Quantitative measurements of the protein binding to telomeric DNA revealed that the presence of both Myb domains is required for a high affinity of YlTay1p to either telomeric repeat. Additionally, we performed detailed thermodynamic analysis of the YlTay1p interaction with its cognate telomeric DNA, which is to our knowledge the first energetic description of a full-length telomeric-protein binding to DNA. Interestingly, when compared with human TRF1 and TRF2 proteins, YlTay1p exhibited higher affinity not only for Y. lipolytica telomeres but also for human telomeric sequences. The duplication of the Myb domain region in YlTay1p thus produces a synergistic effect on its affinity toward the cognate telomeric sequence, alleviating the need for homodimerization observed in TRF-like proteins possessing a single Myb domain.

Aleuria aurantia lectin is a fungal protein composed of two identical 312-amino acid subunits that specifically recognizes fucosylated glycans. The crystal structure of the lectin complexed with fucose reveals that each monomer consists of a six-bladed beta-propeller fold and of a small antiparallel two-stranded beta-sheet that plays a role in dimerization. Five fucose residues were located in binding pockets between the adjacent propeller blades. Due to repeats in the amino acid sequence, there are strong similarities between the sites. Oxygen atoms O-3, O-4, and O-5 of fucose are involved in hydrogen bonds with side chains of amino acids conserved in all repeats, whereas O-1 and O-2 interact with a large number of water molecules. The nonpolar face of each fucose residue is stacked against the aromatic ring of a Trp or Tyr amino acid, and the methyl group is located in a highly hydrophobic pocket. Depending on the precise binding site geometry, the alpha- or beta-anomer of the fucose ligand is observed bound in the crystal. Surface plasmon resonance experiments conducted on a series of oligosaccharides confirm the broad specificity of the lectin, with a slight preference for alphaFuc1-2Gal disaccharide. This multivalent carbohydrate recognition fold is a new prototype of lectins that is proposed to be involved in the host recognition strategy of several pathogenic organisms including not only the fungi Aspergillus but also the phytopathogenic bacterium Ralstonia solanacearum.