Figure 11.

Transport model of LPS and CTD proteins. The first initiation enzymes of UndPP-glycan for two LPSs in Porphyromonas gingivalis are WbaP-like proteins (PGN_1896 and PGN_1233). Assembly of UndPP-glycans is achieved at cytoplasmic side of the inner membrane, and the block is then transported onto the periplasmic side of the inner membrane by Wzx (PGN_1033). The nonrandom (modal) chain length of O-antigen is dictated by Wzy and Wzz proteins, which correspond to an O-antigen polymerase (PGN_1242) and O-antigen chain length regulator (PGN_2005), respectively. Then, O-antigen is ligated to preformed lipid A-cores by O-antigen ligase (PGN_1302), resulting in LPS. LPS is transported to the outer membrane by LPS transport proteins, which are poorly characterized in P. gingivalis. The C-terminal domain proteins are transported to the outer membrane by Sec and the Por secretion system/Type IX secretion system (PorSS/T9SS). Currently, the precise glycosylation mechanism of the CTD proteins remains uncertain.