Cysteine-rich domain of the secreted frizzled-related protein 3 (SFRP3, alias FRZB), a Wnt antagonist.
The cysteine-rich domain (CRD) is an essential part of the secreted frizzled-related protein 3 (SFRP3, alias FRZB), which plays important roles in embryogenesis and postnatal development as an antagonist of Wnt proteins, key players in a number of fundamental cellular processes. SFRPs antagonize the activation of Wnt signaling by binding to the CRD domains of frizzled proteins (Fz), thereby preventing Wnt proteins from binding to these receptors. SFRPs are also known to have functions unrelated to Wnt, as enhancers of procollagen cleavage by the TLD proteinases. SFRPs and Fz proteins both contain CRD domains, but SFRPs lack the seven-pass transmembrane domain which is an integral part of Fzs. SFRP3 regulates Wnt signaling activity in bone development and homeostasis. It is also involved in the control of planar cell polarity.