Cysteine-rich domain of the secreted frizzled-related protein 4 (SFRP4), a Wnt antagonist.
The cysteine-rich domain (CRD) is an essential part of the secreted frizzled-related Protein 4 (SFRP4), which regulates the activity of Wnt proteins, key players in a number of fundamental cellular processes such as embryogenesis and postnatal development. SFRPs antagonize the activation of Wnt signaling by binding to the CRDs domains of frizzled (Fz) proteins, 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.