Members of the antigen I/II family are adhesins with a glucan-binding domain, two types of repetitive regions, an isopeptide bond-forming domain associated with shear resistance, and a C-terminal LPXTG motif for anchoring to the cell wall. They occur in oral Streptococci, and tend to be major cell surface adhesins. Members of this family include SspA and SspB from Streptococcus gordonii, antigen I/II from S. mutans, etc.
Jiyao W et al.(2023). "The conserved domain database in 2023.",