Frizzled-CRD structure

Frizzled

Frizzled is a transmembrane Wnt receptor with 7 transmembrane ahlpha helices and an extracellular Cysteine rich domain (CRD) to which the Wnt binds.

In the CRD, which will be discussed here, all cysteine residues in the structure form disulphide bonds. furthermore there are two short beta strands forming a minimal beta sheet. Apart from this minimal beta sheet the rest of the CRD structure is dominated by alpha helices and their inter-helical loops (see Figure 1).
The structure of the Fz-CRD domain is such that it has a deep hydrophobic groove, with many conserved hydrophobic amino acid residues. This is part of binding site one to form a complex with Wnt (further explained in the Wnt-Fz structure and interactions section.

In both binding sites there are some key conserved residues either fully or chemically. To see a multiple sequence alignment between multiple Frizzled CRD receptor types please refer to Figure 2, taken from the supplementary material (Janda et al. 2013)

Figure 1

Cystein rich domain of the Frizzled receptor. Shown in cyan

are the alpha helices. In green the two short beta strands 

forming a minimal beta sheet. In yellow all the cysteins and 

hence the disulphide bridges are shown, and finally in pink

the inter helical loops of the Fz-CRD.

Figure 2 
This multiple sequence alignment taken from supplementary materials shows strictly conserved residues in red and chemically conserved residues in yellow. The numbers above denote which binding site the residues belong to. The secondary structure elements to which the residues belong to is also denoted above. On the  left hand side the Fz type is shown while on the right the amino acid residue number is shown.