PGAM5: A Novel Type of Protein Serine/Threonine Phosphatase That Exists in the Mitochondria

Phosphoglycerate mutase (PGAM) family member 5 (PGAM5) is a member of the PGAM family, the prototypical members of which are enzymes of intermediary metabolism that convert 3-phosphoglycerate to 2-phosphoglycerate in glycolysis. It has recently been found that PGAM5 lacks authentic PGAM activity but possesses protein phosphatase activity highly specific to serine and threonine residues. Depending on its phosphatase activity, PGAM5 activates the stress-activated c-Jun N-terminal kinase (JNK) and p38 MAP kinase pathways through their upstream regulator ASK1. Furthermore, PGAM5 is localized to the mitochondria through its N-terminal transmembrane domain and appears to be involved in the regulation of mitochondrial functions. Here we introduce this novel type of protein phosphatase and discuss its roles as a signaling intermediate.