STRUCTURE AND FUNCTION OF PERIPLASMIC CHAPERONE-LIKE PROTEINS INVOLVED IN THE BIOSYNTHESIS OF K88 AND K99 FIMBRIAE IN ENTEROTOXIGENIC ESCHERICHIA-COLI

The nucleotide sequence of faeE and fanE, two genes involved in the biosynthesis of K88 and K99 fimbriae, respectively, was determined and the amino acid sequence of the FaeE and FanE proteins was deduced. Immunoblotting of subcellular fractions with an antiserum raised against purified FaeE confirmed that FaeE is located in the periplasm. Indications were obtained that FaeE functions as a chaperone-like protein. Its interaction with the fimbrial subunit (FaeG) in the periplasm stabilizes this polypeptide and prevents its degradation by the cell-envelope protease DegP. Furthermore, FaeE prevents the formation of FaeG multimers which cannot be incorporated into fimbriae. The reactions of the FaeE/FaeG dimers with a set of monoclonal antibodies directed against the various epitopes present on K88 fimbriae revealed that the fimbrial subunits associated with FaeE were present in a conformation resembling their native configuration. Indications about the domains in FaeG involved in the interaction with FaeE are discussed.