Late stages of lipid A biosynthesis of Escherichia coli are transfer reactions of lauric acid (C12 : 0) and myristic acid (C14 : 0) to the hydroxyl group of 3-hydroxy-myristic acid (3-OH-C14 : 0). In the previous study we constructed the mutant strains with disrupted C12 : 0-transferase and C14 : 0-transferase genes, and used those mutant strains for the modification of lipid A by the introduction of foreign acyltransferase genes. In the study reviewed here, C14 : 0-transferase gene (lpxL2) of Klebsiella pneumoniae was cloned, and introduced to the mutant strains by transformation to modify the lipid A structure. LPS preparations of the transformants were analyzed through chemical modification and MALDI-TOF mass spectrometry, and were proved to have the lipid A with one C14 : 0, or two C14 : 0, one of which replaced C12 : 0 bound to 3-OH-C14 : 0 at the C2-position of the non-reducing end glucosamine. The IL-6 inducing activity of the LPS with C14 : 0 was measured, and compared with that of the original LPS with C12 : 0. The activity of LPS with C14 : 0 was found to be comparable with that of LPS with C12 : 0, suggesting that C14 : 0 can replace C12 : 0 without changing the immunostimulating activity of lipid A.
