Structural relationship between a bacterial developmental protein and eukaryotic PP2C protein phosphatases

Bacillus subtilis SpollE is a Ser protein phosphatase whose action on the phosphoprotein SpollAA triggers the cell type-specific activation of a sporulation transcription factor. Here we report that SpollE displays sequence similarity to the PP2C family of eukaryotic Ser/Thr protein phosphatases, and that residues common to these proteins are required for the function of both SpollE and TPD1, a yeast PP2C. These findings suggest that SpollE and the PP2C protein phosphatases are structurally related, and reveal a striking formal similarity between the SpollAA regulatory circuit and that of mammalian mitochondrial pyruvate dehydrogenase. This similarity may reflect an evolutionarily conserved mechanism of biological regulation based on the interplay of His protein kinaselike Ser kinases and PP2C-like protein phosphatases.