Identification of a protein complex that assembles lipopolysaccharide in the outer membrane of Escherichia coli.
The outer membrane of most Gram-negative bacteria is made up of LPS, and in nearly all bacteria that contain LPS it is essential for the life of the organism. The lipid portion of this molecule, lipid A, also known as endotoxin, is a potent activator of the innate immune response. More than 50 genes are required to synthesize LPS and assemble it at the cell surface. Enormous progress has been made in elucidating the structure and biosynthesis of LPS, but until recently the cellular components required for its transport from its site of synthesis in the inner membrane to its final cellular location at the cell surface remained elusive. Here we describe the identification of a protein complex that functions to assemble LPS at the surface of the cell. This complex contains two proteins: Imp, already identified as an essential outer-membrane protein implicated in LPS assembly; and another protein, RlpB, heretofore identified only as a rare lipoprotein. We show that RlpB is also essential for cell viability and that the Imp/RlpB complex is responsible for LPS reaching the outer surface of the outer membrane.
Wu
Tao
T
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
McCandlish
Andrew C
AC
Gronenberg
Luisa S
LS
Chng
Shu-Sin
SS
Silhavy
Thomas J
TJ
Kahne
Daniel
D
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D002470:Cell Survival; D004926:Escherichia coli / Q000378:metabolism* / Q000648:ultrastructure; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000737:chemistry / Q000378:metabolism*; D046912:Multiprotein Complexes
D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D008070:Lipopolysaccharides; C475958:LptD protein, E coli; C514179:LptE protein, E coli; D046912:Multiprotein Complexes