Members of this family are predominantly found in tumour necrosis factor receptor superfamily, member 13b (TACI), and are required for binding to the ligands APRIL and BAFF [1].

1: Structures of APRIL-receptor complexes: like BCMA, TACI employs only a single cysteine-rich domain for high affinity ligand binding. Hymowitz SG, Patel DR, Wallweber HJ, Runyon S, Yan M, Yin J, Shriver SK, Gordon NC, Pan B, Skelton NJ, Kelley RF, Starovasnik MA; J Biol Chem. 2005;280:7218-7227. PMID:15542592