A novel streptococcal leucine zipper protein (Lzp) binds to human immunoglobulins

Streptococcus pyogenes is an important pathogen that causes pharyngitis, scarlet fever, rheumatic fever, and streptococcal toxic shock syndrome. To survive within its host, S. pyogenes has developed several immune evasion mechanisms. Here, we identified a novel gene encoding a 66-kDa protein with many leucine zipper motifs, that we call streptococcal leucine zipper protein (Lzp). Lzp was expressed on the bacterial cell surface, and some was detected in the culture medium. Lzp was expressed by all the S. pyogenes strains we tested, but not by group B streptococcal strains. Western blotting and Biacore assay demonstrated that recombinant Lzp bound to human IgA, IgG, IgM, and Lzp. In addition, native-PAGE analysis suggested that the Lzp molecule formed dimer and trimer conformations. Thus, Lzp is a novel immunoglobulin-binding protein that may play a role in helping S. pyogenes escape detection by the host immune system.