ORDERED TRANSLOCATION OF 987P FIMBRIAL SUBUNITS THROUGH THE OUTER-MEMBRANE OF ESCHERICHIA-COLI

The 987P fimbria of enterotoxigenic Escherichia coli is a heteropolyme ric structure,which consists essentially of a major FasA subunit and a minor subunit, the FasG adhesin, The latter harbors the binding moiet y for receptor molecules on piglet intestinal epithelial cells, In thi s study, anti-FasF antibody probes were developed and used to demonstr ate that the FasF protein represents a new minor fimbrial component, F asF was identified in highly purified fimbriae, and its sequence demon strated significant levels of similarity with that of FasA. Immune ele ctron microscopy localized both the FasG and FasF proteins at the fimb rial tip as well as at broken ends and at various intervals along the fimbrial length, The presence of these minor proteins in purified 987P fimbriae was corroborated by enzyme-linked immunosorbent assay inhibi tions, Finally, the use of nonfimbriated fasG, fasF, and fasA mutants indicated that subunit translocation through the outer membrane follow s a specific order, FasG being the first, FasF being the second, and F asA being the third type of exported subunit, Since fimbriae are thoug ht to grow from the base, FasG is proposed to be a tip adhesin and Fas F is proposed to be a linker molecule between the adhesin and the fimb rial shaft, Moreover, export of FasG (or FasF) in the absence of FasF (or FasA) indicates that during the process of fimbrial biogenesis in the outer membrane, translocating events precede the initiation of sub unit heteropolymerization.