Can a bacterial protein bind sugars from both plants and humans?

Details

Burkholderia ambifaria is generally associated with the plant rhizosphere, where it has biocontrol effects on other microorganisms. It also belongs to the Burkholderia cepacia complex, a group of closely related bacteria that cause lung infections in immunocompromised patients and patients with granulomatous disease or cystic fibrosis.

The researchers’ previous work indicated that fucose on human epithelia is a frequent target for lung pathogen lectins and adhesins (Sulák et al., 2011, PLoS Pathog. 7, e1002238). In this laboratory study, analysis of the B. ambifaria genome identified BambL as a putative fucose-binding lectin. The researchers produced the 87-amino-acid protein recombinantly and found that it bound fucosylated oligosaccharides, preferring αFuc1-2Gal epitopes.

Crystal structures showed that BambL associates as a trimer, with two fucose-binding sites per monomer. Its overall fold is a six-bladed β-propeller formed by oligomerization, as in the Ralstonia solanacearum lectin, rather than by sequential domains as in the fungal fucose lectin from Aleuria aurantia.

Microcalorimetry showed very high affinity for small fucosylated glycans (K(D) < 1 μM). BambL bound plant cell wall oligosaccharides and human histo-blood group oligosaccharides H-type 2 and Lewis Y with equivalent efficiency. Binding tests using artificial glycosphingolipid-containing vesicles, human saliva, and lung tissues confirmed recognition of a wide spectrum of fucosylated epitopes, although affinity was lower for biological material from nonsecretor individuals.