The Intrinsic Immunoglobulin G Endopeptidase Activity of Streptococcal Mac-2 Proteins Implies a Unique Role for the Enzymatically Impaired Mac-2 Protein of M28 Serotype Strains

Abstract

IdeS, a secreted cysteine protease of the important human pathogen Streptococcus pyogenes, interferes with phagocytic killing by specifically cleaving the heavy chain of immunoglobulin G (IgG). Two allelic variants of the enzyme have been described, the IgG-specific endopeptidase, IdeS (or Mac-1) and Mac-2, a protein with only weak IgG endopeptidase activity, which has been suggested to interfere with opsonophagocytosis by blocking Fc␥ receptors of phagocytic cells. However, despite the fact that Mac-2 proteins interact with Fc␥ receptors, no inhibition of reactive oxygen species (ROS) production, opsonophagocytosis, or streptococcal killing by Mac-2 has been reported. In the present study, Mac-2 proteins are shown to contain IgG endopeptidase activity indistinguishable from the enzymatic activity exhibited by IdeS/Mac-1 proteins. The earlier reported weak IgG endopeptidase activity appears to be unique to Mac-2 of M28 serotype strains (Mac-2 M28 ) and is most likely due to the formation of a disulfide bond between the catalytic site cysteine and a cysteine residue in position 257 of Mac-2 M28 . Furthermore, Mac-2 proteins are shown to inhibit ROS production ex vivo, independently of the IgG endopeptidase activity of the proteins. Inhibition of ROS generation per se, however, was not sufficient to mediate streptococcal survival in bactericidal assays. Thus, in contrast to earlier studies, implicating separate functions for IdeS and Mac-2 protein variants, the current study suggests that Mac-2 and IdeS are bifunctional proteins, combining Fc␥ receptor binding and IgG endopeptidase activity. This finding implies a unique role for Mac-2 proteins of the M28 serotype, since this serotype has evolved and retained a Mac-2 protein lacking IgG endopeptidase activity.

The Streptococcal Cysteine Protease SpeB Is Not a Natural Immunoglobulin-Cleaving Enzyme

“…Notably, in the presence of SpeB protein, i.e., independently of enzymatic activity, the amount of extracellular ROS is clearly diminished compared to that of the control (Fig. 2B), an observation also reported for IdeS, another streptococcal cysteine protease (38).…”

Staphylococcus aureus Formyl Peptide Receptor–like 1 Inhibitor (FLIPr) and Its Homologue FLIPr-like Are Potent FcγR Antagonists That Inhibit IgG-Mediated Effector Functions

“…It bound soluble FcgRII and FcgRIII and competed with IgG binding (29), as well as prevented the generation of reactive oxygen species by opsonized latex beads. However, in a whole-blood survival assay of S. pyogenes, only Mac-2 with intact IgG endopeptidase activity facilitated bacterial survival (35). To our knowledge, no other bacterial FcgR antagonist has been described; therefore, this is the first study to demonstrate a bacterial FcgR-binding protein that inhibits FcgR-mediated effector functions in vitro, as well as in vivo.…”

Induction of group A Streptococcus virulence by a human antimicrobial peptide

“…The striking increase in HA capsule production observed in several GAS strains in response to LL-37 could, by itself, result in increased resistance to phagocytosis, enhanced invasion across host epithelial barriers, and increased overall virulence (29,30). Similar changes in expression of other CsrRS-regulated genes, such as the antiphagocytic Mac/IdeS and the IL-8 protease PrtS, are likely to further enhance pathogenicity (31)(32)(33). To test this prediction, we assessed the effect of LL-37 on GAS resistance to complement-mediated opsonophagocytic killing using 4 GAS isolates that exhibited moderate to strong up-regulation of capsule and other CsrRS-regulated genes in response to LL-37: strains 854, 94459, 02-123-1579, and SS-108.…”