Identification and Characterization of Novel Human IgG-Degrading Enzymes

The human immune response and factors that modulate it represent challenges and opportunities in many areas of medicine. Examples are the threat of transplant rejection and the reduction of this threat by the administration of a bacterially derived immune evasion enzyme. Streptococcus species secrete proteases of the IdeS/Mac family that efficiently degrade host immunoglobulin G (IgG) to help the bacteria evade the host's immune response. IdeS has recently received interest as a tool for transiently ablating circulating IgG in the context of diverse treatments, including transplantation and gene therapy. Given the wide-ranging utility of IdeS-mediated modulation of the human immune response, we sought to explore sequence-function relationships within the IdeS family in the hopes of identifying IdeS enzymes with therapeutic potential. To this end, we developed and applied a structural bioinformatics workflow and analytical strategy to identify and experimentally characterize novel IdeS homologs with activity against human IgG. Multiple IdeS-like enzymes with a range of human IgG degradation efficiencies were identified and characterized. The efficiencies of these enzymes exhibit a nontrivial dependence on the sequence of the IdeS-IgG binding site, highlighting the complexity of substrate recognition by IdeS. The workflow and data presented here inform basic IdeS enzymology, provide novel starting points for engineering IdeS variants for therapeutic use, and suggest general strategies for efficiently sampling protein sequence space to identify therapeutic enzymes.