This domain is found in ZNRF-3 protein present in Danio rerio. ZNRF-3 is a transmembrane E3 ubiquitin ligase that antagonizes Wnt signalling, the signalling system used to mediate Rspo protein actions. ZNFR3 and RNF43, alongside the Rspo proteins, have emerged as a system with therapeutic potential for a number of pathological processes. This domain is known as the ectodomain [1].

1: Structural and molecular basis of ZNRF3/RNF43 transmembrane ubiquitin ligase inhibition by the Wnt agonist R-spondin. Zebisch M, Xu Y, Krastev C, MacDonald BT, Chen M, Gilbert RJ, He X, Jones EY; Nat Commun. 2013;4:2787. PMID:24225776