This domain is found in Endo-beta-N-acetylglucosaminidase F2 (EndoS) from Streptococcus pyogenes (Swiss:Q48RM3) and similar sequences predominantly found in Firmicutes. EndoS is an immunomodulatory enzyme secreted by the bacteria to remove carbohydrates from IgG antibodies in a highly specific manner, which gives the pathogen a survival advantage over its host. This protein is composed of five distinct protein domains. The domain located at the base of the V-shaped EndoS structure (this entry), also named hybrid Ig domain, is composed of two subdomains. The smaller one is inserted within the loop that connects the LRR domain to the second and third beta strands of the larger subdomain. The latter is a typical Ig domain structurally similar to the interleukin-4 receptor [1,2,3].

1: Crystal structure of Streptococcus pyogenes EndoS, an immunomodulatory endoglycosidase specific for human IgG antibodies. Trastoy B, Lomino JV, Pierce BG, Carter LG, Gunther S, Giddens JP, Snyder GA, Weiss TM, Weng Z, Wang LX, Sundberg EJ; Proc Natl Acad Sci U S A. 2014;111:6714-6719. PMID:24753590

2: Molecular Basis of Broad Spectrum N-Glycan Specificity and Processing of Therapeutic IgG Monoclonal Antibodies by Endoglycosidase S2. Klontz EH, Trastoy B, Deredge D, Fields JK, Li C, Orwenyo J, Marina A, Beadenkopf R, Gunther S, Flores J, Wintrode PL, Wang LX, Guerin ME, Sundberg EJ; ACS Cent Sci. 2019;5:524-538. PMID:30937380

3: Structural basis for the recognition of complex-type N-glycans by Endoglycosidase S. Trastoy B, Klontz E, Orwenyo J, Marina A, Wang LX, Sundberg EJ, Guerin ME; Nat Commun. 2018;9:1874. PMID:29760474