title: Dual orientation of the outer membrane lipoprotein Pal in Escherichia coli.
abstract: Peptidoglycan associated lipoprotein (Pal) of Escherichia coli (E. coli) is a characteristic bacterial lipoprotein, with an N-terminal lipid moiety anchoring it to the outer membrane. Since its discovery over three decades ago, Pal has been well studied for its participation in the Tol-Pal complex which spans the periplasm and has been proposed to play important roles in bacterial survival, pathogenesis and virulence. Previous studies of Pal place the lipoprotein in the periplasm of E. coli, allowing it to interact with Tol proteins and the peptidoglycan layer. Here, we describe for the first time, a subpopulation of Pal which is present on the cell surface of E. coli. Flow cytometry and confocal microscopy detect anti-Pal antibodies on the surface of intact E. coli cells. Interestingly, Pal is surface exposed in an 'all or nothing' manner, such that most of the cells contain only internal Pal, with fewer cells ( < 20  %) exhibiting surface Pal.
authors: 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA.
authors: Lea Vacca
authors: LV
authors: Michel
authors: 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA.
authors: Juliana
authors: J
authors: Shaw
authors: 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA.
authors: Victoria
authors: V
authors: MacPherson
authors: 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA.
authors: David
authors: D
authors: Barnard
authors: 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA.
authors: John
authors: J
authors: Bettinger
authors: 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA.
authors: Brooke
authors: B
authors: D'Arcy
authors: 2Rochester General Hospital Research Institute, 1425 Portland Avenue, Rochester, NY 14621, USA.
authors: Naveen
authors: N
authors: Surendran
authors: 3Department of Anesthesia and Perioperative Care, University of California, San Francisco, 521 Parnassus Avenue, San Francisco, CA, 94143, USA.
authors: Judith
authors: J
authors: Hellman
authors: 2Rochester General Hospital Research Institute, 1425 Portland Avenue, Rochester, NY 14621, USA.
authors: Michael E
authors: ME
authors: Pichichero
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000032:analysis*; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000032:analysis*; D005434:Flow Cytometry; D008074:Lipoproteins / Q000032:analysis*; D008565:Membrane Proteins / Q000032:analysis*; D018613:Microscopy, Confocal; D010457:Peptidoglycan / Q000032:analysis*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; C031163:ExcC protein, E coli; D008074:Lipoproteins; D008565:Membrane Proteins; D010457:Peptidoglycan