outer membrane protein LptO is essential for the O-deacylation of LPS and the co-ordinated secretion and attachment of A-LPS and CTD proteins in Porphyromonas gingivalis

• Published in: Molecular microbiology Vol. 79; no. 5; pp. 1380 - 1401
• Main Authors: Chen, Yu-Yen, Peng, Benjamin, Yang, Qiaohui, Glew, Michelle D, Veith, Paul D, Cross, Keith J, Goldie, Kenneth N, Chen, Dina, O'Brien-Simpson, Neil, Dashper, Stuart G, Reynolds, Eric C
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.03.2011; Blackwell
• Subjects: Acylation; Bacterial Outer Membrane Proteins - chemistry; Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - metabolism; Bacterial proteins; Biological and medical sciences; Enzyme kinetics; Fundamental and applied biological sciences. Psychology; Gram-negative bacteria; Lipids; Lipopolysaccharides - chemistry; Lipopolysaccharides - metabolism; Membranes; Microbiology; Mutation; Periplasm - chemistry; Periplasm - genetics; Periplasm - metabolism; Phosphorylation; Porphyromonas gingivalis; Porphyromonas gingivalis - chemistry; Porphyromonas gingivalis - genetics; Porphyromonas gingivalis - metabolism; Protein Structure, Secondary; Protein Structure, Tertiary; Porphyromonas gingivalis; Membrane protein; Secretion; Lipopolysaccharide; Bacteria; External membrane; Bacteroidaceae
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/j.1365-2958.2010.07530.x

Protein substrates of a novel secretion system of Porphyromonas gingivalis contain a conserved C-terminal domain (CTD) essential for secretion and attachment to the cell surface. Inactivation of lptO (PG0027) or porT produced mutants that lacked surface protease activity and an electron-dense surface layer. Both mutants showed co-accumulation of A-LPS and unmodified CTD proteins in the periplasm. Lipid profiling by mass spectrometry showed the presence of both tetra- and penta-acylated forms of mono-phosphorylated lipid A in the wild-type and porT mutant, while only the penta-acylated forms of mono-phosphorylated lipid A were found in the lptO mutant, indicating a specific role of LptO in the O-deacylation of mono-phosphorylated lipid A. Increased levels of non-phosphorylated lipid A and the presence of novel phospholipids in the lptO mutant were also observed that may compensate for the missing mono-phosphorylated tetra-acylated lipid A in the outer membrane (OM). Molecular modelling predicted LptO to adopt a β-barrel structure characteristic of an OM protein, supported by the enrichment of LptO in OM vesicles. The results suggest that LPS deacylation by LptO is linked to the co-ordinated secretion of A-LPS and CTD proteins by a novel secretion and attachment system to form a structured surface layer.