Analysis of genes encoding two unique type IIa immunoglobulin G-binding proteins expressed by a single group A streptococcal isolate

Abstract

An emm-like gene (emmL) and a fcrA gene from group A streptococcal strain 64/14 (emmL64/14 and fcrA64/14) were amplified by PCR and force cloned into the heat-inducible expression vector pJLA 602. The emmL gene encoded a recombinant protein that bound human IgG1, IgG2, and IgG4 in a nonimmune fashion. This is the reactivity profile of a type IIa IgG-binding protein. The emmL64/14 gene product was antigenically similar to the previously identified high-molecular-weight type IIa IgG-binding protein of strain 64/14 and had an N-terminal sequence identical to that of the wild-type protein. The fcrA gene also encoded a recombinant protein with type IIa functional activity. This protein was similar to the lower-molecular-weight type IIa IgG-binding protein previously isolated from strain 64/14 and was antigenically distinct from the higher-molecular-weight type IIa protein encoded by the emmL64/14 gene. The sequences for both genes including the intervening regions are presented. The emmL gene demonstrates significant homology to other class I emm and emmL genes expressed by opacity factor-negative group A streptococcal isolates. The fcrA gene was found to be homologous to other fcrA genes normally present in opacity factor-positive group A isolates. The sequence upstream of the fcrA gene and the intervening sequence between the end of the fcrA gene and the start of the emmL gene were similar to those reported for other fcrA genes.