Frizzled homolog 1 (FZD1), also known as Frizzled-1, a member of the G-protein-coupled receptor superfamily, mediates Wnt signaling by serving as a co-receptor with LRP-5 for Wnt ligands. The FZD1 protein contains a signal peptide, a cysteine-rich domain in the N-terminal extracellular region, 7 transmembrane domains, and a C-terminal PDZ domain-binding motif.