Purification, reconstitution and characterization of Phosphatidylserine Synthase 2

Phosphatidylserine (PS) is a major acidic phospholipid class in mammalian cells. The PS is synthesized from phosphatidylcholine (PC) and phosphatidylethanolamine (PE), respectively catalyzed by integral membrane proteins PS synthase (PSS) 1 and PSS2. While PSS1 expression is ubiquitous, PSS2 is expressed in a tissue‐specific manner, most abundant in the testis and brain which are also highly enriched with docosahexaenoic acid (DHA, 22:6n‐3). In brain, such concentration of DHA is known to be necessary for proper neuronal function. Using brain microsomes, we have previously shown that DHA‐containing PC is the best substrates for the PSS1 activity, yielding a high level of DHA‐containing PS (18:0, 22:6‐PS, DHA‐PS). To understand the PS biosynthesis at the molecular level, we immuno‐purified functionally active Flag‐PSS2 after expressing it in HEK cells. We found that purified PSS2 produced DHA‐PS most favorably among other fatty acid containing PS species. Biochemical and structural details of PSS2 conferring this specificity are under investigation. This specificity may contribute to the high accumulation of PS in neuronal cells where DHA is highly concentrated. Intramural Program of National Institutes of Health