The 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.
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.
Oral Health Cooperative Research Centre, Melbourne Dental School, and Bio21 Institute, The University of Melbourne, Vic. 3010, Australia.
Yu-Yen
YY
Chen
Benjamin
B
Peng
Qiaohui
Q
Yang
Michelle D
MD
Glew
Paul D
PD
Veith
Keith J
KJ
Cross
Kenneth N
KN
Goldie
Dina
D
Chen
Neil
N
O'Brien-Simpson
Stuart G
SG
Dashper
Eric C
EC
Reynolds
D000215:Acylation; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000737:chemistry / Q000378:metabolism*; D019897:Periplasm / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016966:Porphyromonas gingivalis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
D001425:Bacterial Outer Membrane Proteins; D008070:Lipopolysaccharides