The membrane organization of leukotriene synthesis

Cell signaling leading to the formation of leukotriene (LT)C-4 requires the localization of the four key biosynthetic enzymes on the outer nuclear membrane and endoplasmic reticulum. Whether any macromolecular organization of these proteins exists is unknown. By using fluorescence lifetime imaging microscopy and biochemical analysis, we demonstrate the presence of two distinct multimeric complexes that regulate the formation of LTs in RBL-2H3 cells. One complex consists of multimers of LTC4 synthase and the 5-lipoxy-genase activating protein (FLAP). The second complex consists of multimers of FLAP. Surprisingly, all LTC4 synthase was found to be in association with FLAP. The results indicate that the formation of LTC4 and LTB4 may be determined by the compartmentalization of biosynthetic enzymes in discrete molecular complexes.