This family contains the membrane spanning region of frizzled and smoothened receptors. This membrane region is predicted to contain seven transmembrane alpha helices. Proteins related to Drosophila frizzled (Swiss:P18537) are receptors for Wnt (mediating the beta-catenin signalling pathway) [1], but also the planar cell polarity (PCP) pathway and the Wnt/calcium pathway. The predominantly alpha-helical Cys-rich ligand-binding region (CRD) of Frizzled is both necessary and sufficient for Wnt binding [2]. The smoothened receptor mediates hedgehog signalling [3].

1: A new member of the frizzled family from Drosophila functions as a Wingless receptor. Bhanot P, Brink M, Samos CH, Hsieh JC, Wang Y, Macke JP, Andrew D, Nathans J, Nusse R; Nature 1996;382:225-230. PMID:8717036

2: The Frizzled family: receptors for multiple signal transduction pathways. Huang HC, Klein PS; Genome Biol 2004;5:234. PMID:15239825

3: In vivo evidence that Patched and Smoothened constitute distinct binding and transducing components of a Hedgehog receptor complex. Chen Y, Struhl G; Development 1998;125:4943-4948. PMID:9811578

4: The frizzled motif: in how many different protein families does it occur?. Rehn M, Pihlajaniemi T, Hofmann K, Bucher P; Trends Biochem Sci 1998;23:415-417. PMID:9852758