Localization and function of FanH and FanG, minor components of K99 fimbriae of enterotoxigenic Escherichia coli.

Specific antisera against FanG and against FanH were prepared by immunization with hybrid Cro-LacZ-FanG and Cro-LacZ-FanH proteins, respectively. Immunoblotting with these antisera revealed the presence of FanG and FanH as minor components in purified K99 fimbriae. Mutations were constructed in fanG and fanH and cells defective in FanG or FanH were characterized by ELISA, immunoblotting, adhesion assays and electron microscopy. A minicell experiment showed that the mutations in fanG or fanH had no effect on the expression of the other K99-specific proteins. Cells defective in FanG produced no fimbriae and did not agglutinate horse erythrocytes, but cell-free heat-shock preparations of these cells still bound the K99 glycolipid receptor. Cells defective in FanH produced 1-2% of the K99 fimbriae as compared with wild-type K99 producing cells. These mutant fimbriae appeared to be shorter but were still capable of binding the K99 glycolipid receptor. Apparently, FanG and FanH are not required for binding the K99 receptor. These results and analysis of K99 mutants by immunoblotting using a specific antiserum against another K99 minor component, FanF, indicated that the combinations FanF/FanG and FanF/FanH are required for the initiation and elongation (length determination) of K99 fimbriae formation, respectively.