Fig. 10. Proposed topology of the cleavage and modification of the 1-phosphate group of H. pylori lipid A.
After assembly of Kdo2-lipid A bearing the core oligosaccharide (core-lipid A), the macromolecule is transported across the inner membrane by the ABC transporter, MsbA (28, 67). In H. pylori, the 1-phosphate group of the lipid A domain can then be removed by a specific phosphatase Hp0021. This is followed by the addition of a pEtN unit directly to the glucosamine disaccharide backbone catalyzed by the lipid A pEtN transferase, Hp0022. The predicted membrane topology of Hp0021 and Hp0022 was determined using the program SOSUI (sosui.proteome.bio.tuat.ac.jp/sosuiframe0.html) (75, 76).