Figure 1.

Domain architecture of caspases in metazoans, a paracaspase in human, metacaspases in plants, and type I and type II metacaspases in phytoplankton. The catalytic domains are comprised of p20 and p10 domains and a prodomain, which possesses recruitment domains (for example, CARD or DED in initiator caspases, DD or Ig in a paracaspase and PRR or zinc-finger motifs in plant type I metacaspases). The prodomain is absent in several type I metacaspases in phytoplankton indicating the presence of a prodomain is not a definitive characteristics for type I metacaspases. Caspase-9 and -6 from human are shown as a representative initiator and executioner caspases and AtMC1 and AtMC4 from A. thaliana are presented as plant type I and type II metacaspases. The species abbreviations are: Aa, Aureococcus anophagefferens; Cr, Chlamydomonas. reinhardtii; Eh, Emiliania huxleyi; Gt, Guillardia theta; Tp, Thalassiosira pseudonana; Vc, Volvox carteri f. nagariensis