Molecular Dissection of the Campylobacter jejuni CadF and FlpA Virulence Proteins in Binding to Host Cell Fibronectin

Abstract

<i>Campylobacter jejuni</i>, a zoonotic pathogen that frequently colonizes poultry, possesses two Microbial Surface Components Recognizing Adhesive Matrix Molecule(s) (MSCRAMMs) termed CadF and FlpA that bind to the glycoprotein fibronectin (FN). Previous to this study, it was not known whether the CadF and FlpA proteins were functionally redundant or if both were required to potentiate host cell binding and signaling processes. We addressed these questions by generating a complete repertoire of <i>cadF</i> and <i>flpA</i> mutants and complemented isolates, and performing multiple phenotypic assays. Both CadF and FlpA were found to be necessary for the maximal binding of <i>C. jejuni</i> to FN and to host cells. In addition, both CadF and FlpA are required for the delivery of the <i>C. jejuni</i> Cia effector proteins into the cytosol of host target cells, which in turn activates the MAPK signaling pathway (Erk 1/2) that is required for the <i>C. jejuni</i> invasion of host cells. These data demonstrate the non-redundant and bi-functional nature of these two <i>C. jejuni</i> FN-binding proteins. Taken together, the <i>C. jejuni</i> CadF and FlpA adhesins facilitate the binding of <i>C. jejuni</i> to the host cells, permit delivery of effector proteins into the cytosol of a host target cell, and aid in the rewiring of host cell signaling pathways to alter host cell behavior.