Cysteine-rich Wnt-binding domain (CRD) of receptors similar to frizzled 9.
The cysteine-rich domain (CRD) is an essential extracellular portion of the frizzled 9 (Fz9) and frizzled 10 (Fz10) receptors, and similar proteins. This domain is required for binding Wnt proteins, which play fundamental roles in many aspects of early development, such as cell and tissue polarity, neural synapse formation, and the regulation of proliferation. Fz proteins serve as Wnt receptors for multiple signal transduction pathways, including both beta-catenin dependent and -independent cellular signaling, as well as the planar cell polarity pathway and Ca(2+) modulating signaling pathway. The CRD domain is well conserved in metazoans - 10 frizzled proteins have been identified in mammals, 4 in Drosophila and 3 in Caenorhabditis elegans. Very little is known about the mechanism by which CRD domains interact with their ligands. The domain contains 10 conserved cysteines.