Recombinant Human sFRP-3 Protein

Secreted Frizzled Related Protein 3 (sFRP-3) was originally identified in bovine cartilage for its chondrogenic ability. Human, mouse, chick and Xenopus clones have also been isolated. SFRP-3 is often referred to as FRZB, other names include Fritz, Frzb1, and FRP-3. At the amino acid sequence level, sFRP-3 is highly conserved. The human protein shares 77% identity with Xenopus, 92% with mouse, and 94% with bovine proteins. Human sFRP-3 is strongly expressed in the developing appendicular skeleton, and cartilage of craniofacial bones. As determined by Northern blot of adult tissues, it is strongly detected in heart and placenta, as well as the brain, skeletal muscle, kidney and pancreas.

The N-terminal portion of the protein shows 50% amino acid identity to the corresponding region of the Drosophila frizzled gene product, a receptor for Wg/Wnt signals. The similarity of sFRP-3 with frizzled proteins is restricted to the N-terminal cysteine-rich domain (CRD) that contains at least ten cysteine residues with highly conserved spacing between them. SFRP-3 was subsequently shown to be a soluble antagonist of Wnt signals. It lacks all transmembrane domains of frizzled proteins but retains the ability to bind Wnts. Ectopic expression of sFRP-3 mRNA has been shown to interfere with the induction of secondary axes in Xenopus embryos injected with Xwnt-8 mRNA.