Interaction of Helicobacter pylori Cell Membrane with Non-Esterified Cholesterol and Other Steroids

Abstract

Helicobacter pylori performs the unique action of assimilating exogenous non-esterified cholesterol into its cell mem-brane. This bacterium aggressively incorporates non-esterified cholesterol into the membrane, induces its glucosylation, and uses both non-esterified cholesterol and glucosylated cholesterols as membrane lipid compositions. The reason for this assimilation of non-esterified cholesterol into the cell membrane of H. pylori has eluded investigators for many years. Recent hypotheses posit that the sterol-uptake and sterol-glucosylation contribute to the survival of H. pylori cells in different ways. The incorporation of the non-esterified cholesterol into the cell membrane fortifies the resistance of H. pylori against the antibacterial actions of phosphatidylcholines, antibiotics, and bile salts. In parallel, the glucosylation of the non-esterified cholesterol incorporated into the cell membrane serves H. pylori in two ways. First, it helps the bacterium evade host immune responses, such as phagocytosis by macrophages and activation of antigen-specific T cells. Second, it detoxifies sterols fatal to the bacterium via a novel action of sterol glucosylation recently described in another report from our group. The reluctance of H. pylori to absorb esterified cholesterol remains unexplained. A re-cent study by our group has demonstrated that the phosphatidylethanolamine (PE) in the outer membrane of H. pylori serves as a steroid-binding lipid the incorporation of non-esterified cholesterol into the membrane. We have also dis-covered that the myristic acid (C 14:0) molecule attached to the PE of this bacterium plays an important role in the selec-tive binding of non-esterified cholesterol but not esterified cholesterol.