Abstract
Helicobacter pylori performs the unique action of assimilating exogenous non-esterified cholesterol into its cell membrane. 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 recent 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 discovered that the myristic acid (C14:0) molecule attached to the PE of this bacterium plays an important role in the selective binding of non-esterified cholesterol but not esterified cholesterol.
Highlights
Helicobacter pylori, a Gram-negative curved rod, is a pathogen responsible for chronic gastritis and peptic ulcers in humans [1,2]
The cell membrane of H. pylori glucosylates non-esterified cholesterol and other 3β-OH steroid compounds via at least two pathways: first, via the direct binding of 3β-OH steroid compounds to the CGT protein followed by glucosylation; second, via the transport of 3β-OH steroid compounds to the CGT protein after the binding of those compounds to the PE for glucosylation
It remains unclear whether H. pylori cells possess a transport molecule that carries the 3β-OH steroid compounds from the PE molecules to the CGT proteins
Summary
Helicobacter pylori, a Gram-negative curved rod, is a pathogen responsible for chronic gastritis and peptic ulcers in humans [1,2]. While sterols are generally unnecessary for the growth or viability of bacteria, a few bacterial species assimilate exogenous non-esterified cholesterol into their cell membranes and glucosylate it once assimilated. While H. pylori attaches a D-glucose molecule to a cholesterol molecule absorbed into the cell membrane via α-glucosidic linkage, Borrelia hermsii attaches its sugar molecule to a cholesterol molecule via β-glucosidic linkage [22], as with the glucosyl sterols in plants and fungi. The O-glycoside bond between sugar molecule and sterol molecule in H. pylori differs from the O-glycoside bond between the same two molecules in other organisms It has long been unclear why H. pylori needs to assimilate non-esterified cholesterol into its cell membrane. This review article describes the biological significance of the cholesterol uptake and glucosylation for the survival of H. pylori, and the interaction of the H. pylori cell membrane with other steroid compounds
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