| Modification Notes |
Phosphatidylserine synthases (PSS) are widespread, ancestral enzymes with a highly conserved function. PSS is a membrane protein responsible for catalyzing the calcium-dependent base exchange of serine with existing phospholipid head groups in the biosynthesis of phosphatidylserine (PtdSer), a major anionic phospholipid expressed on the inner layer of the plasma membrane. Two forms of PSS exist, PSS1 and PSS2, both localizing to the mitochondria-associated membrane. These two forms are encoded by different genes but share very similar characteristics, differing only in their substrate specificity. The primary substrate for PSS1 is phosphatidylcholine and the substrate for PSS2 is phosphatidylethanolamine. PSS1 and PSS2 are directly inhibited by PtdSer and this inhibition is important for feedback control of PtdSer synthesis. Cells overexpressing PSS1 and PSS2 are significantly resistant to UV-induced apoptosis. |