This family is found in metazoa, and is very similar to the fibronectin type III domain. The family is found in cytokine receptors, interleukin and interferon receptors and coagulation factor III proteins. It occurs multiple times, as does fn3, family Pfam:PF00041.

1: The crystal structure of the extracellular domain of human tissue factor refined to 1.7 A resolution. Muller YA, Ultsch MH, de Vos AM; J Mol Biol 1996;256:144-159. PMID:8609606