Lectins play important roles in infections by pathogenic bacteria, for example, in host colonization, persistence, and biofilm
formation. The Gram-negative entomopathogenic bacterium
Photorhabdus luminescens symbiotically lives in insect-infecting Heterorhabditis nematodes and kills the insect host upon
invasion by the nematode. The P. luminescens genome harbors
the gene plu2096, coding for a novel lectin that we named PllA.
We analyzed the binding properties of purified PllA with a glycan array and a binding assay in solution. Both assays revealed a
strict specificity of PllA for -galactoside–terminating glycoconjugates. The crystal structures of apo PllA and complexes
with three different ligands revealed the molecular basis for the
strict specificity of this lectin. Furthermore, we found that a 90°
twist in subunit orientation leads to a peculiar quaternary structure compared with that of its ortholog LecA from Pseudomonas
aeruginosa.We also investigated the utility of PllA as a probe for
detecting -galactosides. The -Gal epitope is present on wildtype pig cells and is the main reason for hyperacute organ rejection in pig to primate xenotransplantation. We noted that PllA
specifically recognizes this epitope on the glycan array and demonstrated that PllA can be used as a fluorescent probe to detect
this epitope on primary porcine cells in vitro. In summary, our
biochemical and structural analyses of the P. luminescens lectin
PllA have disclosed the structural basis for PllA’s high specificity for -galactoside–containing ligands, and we show that PllA
can be used to visualize the -Gal epitope on porcine tissues
