The Salmonella SPI-2 effector SseJ exhibits eukaryotic activator-dependent phospholipase A and glycerophospholipid : cholesterol acyltransferase activity

Intracellular replication of Salmonella enterica serovar Typhimurium within membrane-bound compartments, called Salmonella-containing vacuoles, depends on the activities of several effector proteins translocated by the Salmonella pathogenicity island 2 (SPI-2)-encoded type III secretion system. The SPI-2 effector protein SseJ shows similarity at the amino acid level to several GDSL lipases with glycerophospholipid : cholesterol acyltransferase (GCAT) activity. In this study, we show that catalytic serine-dependent phospholipase A (PLA) and GCAT activity of recombinant SseJ is potentiated by factor(s) present in HeLa cells, RAW macrophages and Saccharomyces cerevisiae. SseJ activity was enhanced with increasing amounts of, or preincubation with, eukaryotic cell extracts. Analysis of the activating factor(s) shows that it is soluble and heat- and protease-sensitive. We conclude that PLA and GCAT activities of SseJ are potentiated by proteinaceous eukaryotic factor(s).