K88ab gene of Escherichia coli encodes a fimbria-like protein distinct from the K88ab fimbrial adhesin.

The K88ab adhesin operon of Escherichia coli encodes for a fimbrial protein (the K88ab adhesin) which is involved in colonization of the porcine intestine. We characterized a structural gene (gene A) which is part of the K88ab adhesin operon and codes for an as yet unidentified polypeptide (pA). A mutation in gene A resulted in accumulation of K88ab adhesin subunits inside the cell. The nucleotide sequence of gene A was determined, and the deduced amino acid sequence suggested that pA is synthesized as a precursor containing a typical N-terminal signal peptide. The molecular weight of pA was calculated to be ca. 17,600. Gene A is preceded by a sequence showing homology with the consensus promoter. Fimbrial subunits from a number of E. coli strains have significant homology at their N- and C-termini. pA also contained some of these conserved sequences and showed a number of other similarities with fimbrial subunits. Therefore, it seems likely that the K88ab adhesin operon codes for a fimbrial subunit (pA) distinct from the K88ab adhesin subunit.