Members of this family, which are predominantly found in the prokaryotic protein quinohemoprotein amine dehydrogenase, adopt an immunoglobulin-like beta-sandwich fold, with seven strands arranged into two beta sheets; the fold is possibly related to the immunoglobulin and/or fibronectin type III superfamilies. The precise function of this domain has not, as yet, been defined [1,2].

1: Structure of the phenylhydrazine adduct of the quinohemoprotein amine dehydrogenase from Paracoccus denitrificans at 1.7 A resolution. Datta S, Ikeda T, Kano K, Mathews FS; Acta Crystallogr D Biol Crystallogr. 2003;59:1551-1556. PMID:12925784

2: Crystal structure of quinohemoprotein amine dehydrogenase from Pseudomonas putida. Identification of a novel quinone cofactor encaged by multiple thioether cross-bridges. Satoh A, Kim JK, Miyahara I, Devreese B, Vandenberghe I, Hacisalihoglu A, Okajima T, Kuroda S, Adachi O, Duine JA, Van Beeumen J, Tanizawa K, Hirotsu K; J Biol Chem. 2002;277:2830-2834. PMID:11704672