Evolutionary variation in ADAMTS13 structure. The domain architecture of ADAMTS13 was determined for 264 species listed in supplemental Table 1. The apparent ancestral structure, with a long propeptide and a total of 9 T domains, is indicated at the top. Domains T3, T6a, and T6 (shaded yellow) have been deleted independently several times in different lineages. Other representative structures are shown for selected vertebrates. Names in bold indicate species or groups from which plasma samples were available for ADAMTS13 assays.