Cysteine-rich domain of the secreted frizzled-related protein 1 (SFRP1), a regulator of Wnt activity.
The cysteine-rich domain (CRD) is an essential part of the secreted frizzled-related protein 1 (SFRP1), 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. SFRP1 is expressed in many tissues and is involved in the regulation of Wnt signaling in osteoblasts, leading to enhanced trabecular bone formation in adults; it has also been shown to control the growth of retinal ganglion cell axons and the elongation of the antero-posterior axis.