Blood group antigen recognition by a Streptococcus pneumoniae virulence factor.

The Streptococcus pneumoniae fucose utilization operon includes a gene encoding a virulence factor that belongs to family 98 in the glycoside hydrolase classification. This protein contains a C-terminal triplet of fucose binding modules that have significant amino acid sequence identity with the Anguilla anguilla fucolectin. Functional studies of these fucose binding modules reveal binding to fucosylated oligosaccharides and suggest the importance of multivalent binding. The high resolution crystal structures of ligand bound forms of one fucose binding module uncovers the molecular basis of fucose, ABH blood group antigen, and Lewisy antigen binding. These studies are extended by fluorescence microscopy to show specific binding to mouse lung tissue. These modules define a new family of carbohydrate binding modules now classified as family 47.