The PPP phosphatases have bimetallic actives sites with Fe and Zn (or Mn) and are related in sequence, structure and mechanism to the purple acid phosphatases. Genomics has shown that the PPP enzymes are extraordinarily conserved in all eukaryotes (e.g. mammals, Xenopus, Drosophila, C. elegans, S. pombe, S. cerevisiae). Humans and yeast have about the same total number of PPP genes, in separate functional classes (i.e. PP1, PP2A, PP4, PP6). These classes of PPP are all sensitive to inhibition by nanomolar concentrations of toxins such as calyculin A, okadaic acid, microcystin and cantharidin, produced by marine dinoflagellates, or blue-green algae, or insects. We use these toxins as experimental tools. Individual human PPP proteins can substitute in place of their yeast homologues, but not PPP of other functional classes, showing that individual PPP are functionally equivalent across evolution, but each class has distinctive biological actions. The conservation across species allows us to use the results from genetic experiments in various model organisms to guide our study the human versions of PPPs.
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