Biosynthesis of K88 fimbriae in Escherichia coli: interaction of tip-subunit FaeC with the periplasmic chaperone FaeE and the outer membrane usher FaeD.

K88 fimbriae are ordered polymeric protein structures at the surface of enterotoxigenic Escherichia coli cells. Their production and assembly requires a molecular chaperone located in the periplasm (FaeE) and a molecular usher located in the outer membrane (FaeD). FaeC is the tip component of the K88 fimbriae.

Epitope tagging analysis of the outer membrane folding of the molecular usher FaeD involved in K88 fimbriae biosynthesis in Escherichia coli.

To analyse the outer membrane folding of the molecular usher FaeD, tagged derivatives were prepared and their expression, tag-localisation and functioning in K88 fimbriae biosynthesis was studied. A semi-random insertion mutagenesis approach with factor Xa cleavage sites yielded six tagged FaeD derivatives. A site-directed mutagenesis approach in which c-myc epitopes were inserted yielded twenty-one different derivatives.

The N-terminal beta-barrel domain of the Escherichia coli K88 periplasmic chaperone FaeE determines fimbrial subunit recognition and dimerization.

The K88 periplasmic chaperone FaeE is a homodimer, whereas the K99 chaperone FanE is a monomer. The structural requirements for dimerization of the K88 fimbrial periplasmic chaperone and for fimbrial subunit-binding specificity were investigated by analysis of mutant chaperones. FaeE contains a C-terminal extension of 19 amino acid residues when compared to FanE and most other fimbrial chaperones.