The Frizzled CRD (cysteine rich domain) is conserved in diverse proteins including several receptor tyrosine kinases
[1, 2, 3].
In Drosophila melanogaster, members of the Frizzled family of tissue-polarity genes encode proteins that appear to function as cell-surface receptors for Wnts. The Frizzled genes belong to the seven transmembrane class of receptors (7TMR) and have in their extracellular region a cysteine-rich domain that has been implicated as the Wnt binding domain. Sequence similarity between the cysteine-rich domain of Frizzled and several receptor tyrosine kinases, which have roles in development, include the muscle-specific receptor tyrosine kinase (MuSK), the neuronal specific kinase (NSK2), and ROR1 and ROR2.
The structure of this domain is known and is composed mainly of alpha helices.
This domain contains ten conserved cysteines that form five disulphide bridges.
Dann CE, Hsieh JC, Rattner A, Sharma D, Nathans J, Leahy DJ.
Insights into Wnt binding and signalling from the structures of two Frizzled cysteine-rich domains.
Nature 412 2001 86-90
[PubMed: 11452312] http://dx.doi.org/10.1038/35083601