This is an immunoglobulin domain which can be found in Interleukin-18 receptor alpha (IL-18Ra). IL-18Ra ectodomain folds into three immunoglobulin (Ig)-like domains, similar to IL-1 receptors. Each domain comprises a two-layer sandwich of six to nine beta-strands and contains at least one intra-domain disulfide bond [1].

1: The structural basis for receptor recognition of human interleukin-18. Tsutsumi N, Kimura T, Arita K, Ariyoshi M, Ohnishi H, Yamamoto T, Zuo X, Maenaka K, Park EY, Kondo N, Shirakawa M, Tochio H, Kato Z; Nat Commun. 2014;5:5340. PMID:25500532