They encode seven-transmembrane
proteins which act as receptors for
secreted Wnt glycoproteins
(reviewed in [1]). All Frizzled
proteins share the following
structural similarities: a signal
sequence at the amino terminus; a
conserved region of 120 amino acids
in the extracellular domain
containing a motif of 10 invariantly
spaced cysteines (called the
cysteine-rich domain or CRD); a
seven-pass transmembrane region,
in which the transmembrane
segments are well conserved; and a
cytoplasmic domain with little
homology among members of the
family. The CRD domain has been