Figure 3: Characteristics of the ZNRF3 dimer and Rspo–ZNRF3 complex interfaces.

(a) An open book view of the ZNRF3–Rspo interface. The surface contributing to the interface is coloured green on ZNRF3_ecto and Rspo_Fu1–Fu2; within this, surface mutants tested in this study are highlighted in red (top). Rspo and ZNRF3_ecto coloured by electrostatic surface potential from red (acidic) to blue (basic) (middle). Sequence conservation across species coloured from white (not conserved) to black (conserved). (b) Disease-related mutations are plotted onto the molecular surface of Rspo (top) and ZNRF3/RNF43 (bottom), and are concentrated at the Rspo–ZNRF3/RNF43 interaction interface. Tumour-associated missense mutations derived from the cosmic database ( http://cancer.sanger.ac.uk/cancergenome/projects/cosmic/) are shown in red and missense mutations causal for congenital anonychia on RSPO4 are shown in orange. Sites in orange on ZNRF3 are mutations of RNF43 that map to the dimer interface of ZNRF3. Numbers 1–4 in parentheses indicate mutations found in RSPO1 to RSPO4 (top). Number 3 and 43 in parentheses indicate mutations found in ZNRF3 and RNF43, respectively (bottom).