Identification of small subunit of serine palmitoyltransferase a as a lysophosphatidylinositol acyltransferase 1‐interacting protein

Lysophosphatidylinositol acyltransferase 1 ( LPIAT 1), also known as MBOAT 7, is a phospholipid acyltransferase that selectively incorporates arachidonic acid ( AA ) into the sn ‐2 position of phosphatidylinositol ( PI ). We previously demonstrated that LPIAT 1 regulates AA content in PI and plays a crucial role in brain development in mice. However, how LPIAT 1 is regulated and which proteins function cooperatively with LPIAT 1 are unknown. In this study, using a split‐ubiquitin membrane yeast two‐hybrid system, we identified the small subunit of serine palmitoyltransferase a (ss SPT a) as an LPIAT 1‐interacting protein. ss SPT a co‐immunoprecipitated and colocalized with LPIAT 1 in cultured mammalian cells. Knockdown of ss SPT a decreased the LPIAT 1‐dependent incorporation of exogenous AA into PI but did not affect the in vitro enzyme activity of LPIAT 1 in the microsomal fraction. Interestingly, knockdown of ss SPT a decreased the protein level of LPIAT 1 in the crude mitochondrial fraction but not in total homogenate or the microsomal fraction. LPIAT 1 was localized to the mitochondria‐associated membrane ( MAM ), where AA ‐selective acyl‐CoA synthetase is enriched. These results suggest that ss SPT a plays a role in fatty acid remodeling of PI , probably by facilitating the MAM localization of LPIAT 1.