C3 binding domain 4 of IgG-bind protein SBI
This family of proteins represents Sbi domain IV which binds the central complement protein C3. Sbi-IV interacts with Sbi-III to induce a consumption of complement via alternative pathway activation. When not interacting with Sbi-III, Sbi-IV inhibits the alternative pathway without complement consumption. The structure of Sbi-IV consists of a three-helix bundle fold.
Jiyao W et al.(2023). "The conserved domain database in 2023.",