Braun's lipoprotein
Braun's lipoprotein (BLP, Lpp, or murein lipoprotein), found in some gram-negative cell walls, is one of the most abundant membrane proteins; its molecular weight is about 7.2 kDa. It is bound at its C-terminal end (a lysine) by a covalent bond to the peptidoglycan layer (specifically to diaminopimelic acid molecules[1]) and is embedded in the outer membrane by its hydrophobic head (a cysteine with lipids attached). BLP tightly links the two layers and provides structural integrity to the outer membrane.
Characteristics
The gene encoding Braun's lipoprotein initially produces a protein composed of 78 amino acids, which includes a 20 amino acid signal peptide at the amino terminus.[2] The mature protein is 6 kDa in size.[3] Three monomers of Lpp assemble into a coiled-coil trimer.[4]
Large amounts of Braun's lipoprotein is present, more than any other protein in E. coli.[5] Unlike other lipoproteins, it is linked covalently to the peptidoglycan.[4] Lpp connects the outer membrane to the peptidoglycan. Lpp is anchored to the outer membrane by its amino-terminal lipid group. In E. coli, one third of Lpp proteins form a peptide bond via the side chain of its carboxy-terminal lysine with diaminopimelic acid in the peptidoglycan layer.[5][6] The rest of the Lpp molecules are present in a "free" form unlinked to peptidoglycan. The free form is exposed on the surface of E. coli.[3]
Functions
Lpp, along with another lipoprotein called Pal, maintains the stability of the cell envelope by attaching the outer membrane to the cell wall.[3]
Lpp has been proposed as a virulence factor of Yersinia pestis, the cause of plague.[7] Y. pestis needs lpp for maximum survival in macrophages and to efficiently kill mouse models of bubonic and pneumonic plague.[8]
Immunology
Braun's lipoprotein binds to the pattern recognition receptor TLR2. Lpp induces adhesion of neutrophils to human endothelial cells by activating the latter.[9]
References
- ^ Seltmann, Guntram; Holst, Otto (2002). The Bacterial Cell Wall. Berlin: Springer. pp. 81–82. ISBN 3-540-42608-6.
- ^ Dramsi S, Magnet S, Davison S, Arthur M (2008). "Covalent attachment of proteins to peptidoglycan". FEMS Microbiology Reviews. 32 (2): 307–20. doi:10.1111/j.1574-6976.2008.00102.x. PMID 18266854.
- ^ a b c Konovalova A, Silhavy TJ (2015). "Outer membrane lipoprotein biogenesis: Lol is not the end". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 370 (1679). doi:10.1098/rstb.2015.0030. PMC 4632606. PMID 26370942.
- ^ a b Kovacs-Simon A, Titball RW, Michell SL (2011). "Lipoproteins of bacterial pathogens". Infection and Immunity. 79 (2): 548–61. doi:10.1128/IAI.00682-10. PMC 3028857. PMID 20974828.
- ^ a b Silhavy TJ, Kahne D, Walker S (2010). "The bacterial cell envelope". Cold Spring Harbor Perspectives in Biology. 2 (5): a000414. doi:10.1101/cshperspect.a000414. PMC 2857177. PMID 20452953.
- ^ Vollmer, Waldemar (2007). "Structure and biosynthesis of the murein (peptidoglycan) sacculus". In Ehrmann, Michael (ed.). The Periplasm ([Online-Ausg.]. ed.). Washington, DC: ASM Press. pp. 198–213. ISBN 9781555813987.
- ^ Butler T (2009). "Plague into the 21st century". Clinical Infectious Diseases. 49 (5): 736–42. doi:10.1086/604718. PMID 19606935.
- ^ Smiley ST (2008). "Immune defense against pneumonic plague". Immunological Reviews. 225: 256–71. doi:10.1111/j.1600-065X.2008.00674.x. PMC 2804960. PMID 18837787.
- ^ McIntyre TM, Prescott SM, Weyrich AS, Zimmerman GA (2003). "Cell-cell interactions: leukocyte-endothelial interactions". Current Opinion in Hematology. 10 (2): 150–8. doi:10.1097/00062752-200303000-00009. PMID 12579042.