Extensive substrate recognition by the streptococcal antibody-degrading enzymes IdeS and EndoS

Abstract

Enzymatic cleavage of IgG antibodies is a common strategy used by pathogenic bacteria to ablate immune effector function. The Streptococcus pyogenes bacterium secretes the protease IdeS and the glycosidase EndoS, which specifically catalyse cleavage and deglycosylation of human IgG, respectively. IdeS has received clinical approval for kidney transplantation in hypersensitised individuals, while EndoS has found application in engineering antibody glycosylation. Here, we present crystal structures of both enzymes in complex with their IgG1 Fc substrate, which was achieved using Fc engineering to disfavour preferential Fc crystallisation. The IdeS protease displays extensive Fc recognition and encases the antibody hinge. Conversely, the glycan hydrolase domain in EndoS traps the Fc glycan in a flipped-out conformation, while additional recognition of the Fc peptide is driven by the so-called carbohydrate binding module. Understanding the molecular basis of antibody recognition by bacterial enzymes will facilitate the development of next-generation enzymes for clinical and biotechnological use.