FIGURE 3.

Structural similarity dendrogram and heatmap for a selection of V-set IgSF domains, based on SSAP scores. Domains are identified by the common short names of the proteins in which they occur, with the identifier and chain letter for the PDB structure used for comparison in brackets. Domains were ordered according to a dendrogram constructed using complete hierarchical clustering based on scores obtained from pairwise structural comparisons using SSAP (43). Colors in the heatmap range from red to dark green for high and low structural similarity, respectively (see color key). A histogram in the color key panel shows the frequency distribution of SSAP scores in the set. Color bars on the left and upper sides of the heatmap indicate known functional or family groupings: green, CTLA-4; yellow, other members of the costimulatory/inhibitory family; red, antigen receptors; pink, coreceptors; dark blue, CD2 family; light blue, B7 family; black, outgroup (C1 and C2 set IgSF domains); gray, other V-set proteins.