Nonimmune Binding of Human Immunoglobulin A (IgA) and IgG Fc by Distinct Sequence Segments of the EibF Cell Surface Protein of Escherichia coli

ABSTRACT The eib genes of Escherichia coliencode surface-exposed proteins which bind immunoglobulins (Ig) such as the Fc fragment of human IgG (IgG Fc) in a nonimmune manner. The Eib proteins belong to a family which includes YadA ofYersinia, UspA2 of Moraxella, and DsrA ofHaemophilus ducreyi. This family of surface-exposed proteins shares several features, such as the ability to impart resistance to human serum complement and a tendency to exist as stable multimers. Four genes, eibA, eibC,eibD and eibE, were previously identified and cloned from ECOR-9, a strain from the E. colireference collection. EibC, -D, and -E bind human serum IgA in addition to IgG, but no IgA binding has been observed for EibA. Here, we report the cloning of a new eib gene, eibF, from a second strain of E. coli, ECOR-2. The product, EibF, has a relatively strong preference for IgA. Like the othereib genes, eibF attenuates serum sensitivity, occurs as a stable multimer, and is associated with a prophage. By subcloning portions of the eibA andeibF genes, we have identified distinct sequence segments sufficient to cause Ig binding, multimerization, and discrimination between IgA and IgG. The ability to multimerize is associated with a sequence close to the C terminus that is homologous to other family members such as YadA. Binding of IgG Fc is associated with a sequence that is highly conserved among all Eib proteins but otherwise unique. Binding of IgA is associated with a sequence of EibF that is not similar to any EibA sequence.