Identification of the specific oligosaccharide sites recognized by type 1 fimbriae from Escherichia coli on nonspecific cross-reacting antigen, a CD66 cluster granulocyte glycoprotein.

Nonspecific cross-reacting antigen (NCA), a CD66 cluster antigen, is a well characterized glycoprotein on granulocytes, macrophages, and lung epithelium. Structural studies at the protein and genomic levels have revealed that NCA is a member of the immunoglobulin (Ig) supergene family and contains a domain structure similar to Ig with an amino-terminal variable-like domain followed by disulfide loop-containing constant-like domains. Previous work by this laboratory and others has demonstrated that NCA is a receptor for binding of bacteria expressing type 1 fimbriae (pili). This binding is mediated by interaction between lectins on the bacteria fimbriae and carbohydrate chains on NCA. In the present work we further characterize the specificity for bacterial binding by NCA using endoglycosidases and site-directed mutagenesis. Results of these studies demonstrate that Escherichia coli expressing type 1 fimbriae binds to high mannose oligosaccharide structures on NCA and that the functionally relevant sites are located in the variable-like domain of NCA.