title: Dynamic lipopolysaccharide transfer cascade to TLR4/MD2 complex via LBP and CD14.
abstract: Toll-like receptor 4 (TLR4) together with MD2, one of the key pattern recognition receptors for a pathogen-associated molecular pattern, activates innate immunity by recognizing lipopolysaccharide (LPS) of Gram-negative bacteria. Although LBP and CD14 catalyze LPS transfer to the TLR4/MD2 complex, the detail mechanisms underlying this dynamic LPS transfer remain elusive. Using negative-stain electron microscopy, we visualized the dynamic intermediate complexes during LPS transfer-LBP/LPS micelles and ternary CD14/LBP/LPS micelle complexes. We also reconstituted the entire cascade of LPS transfer to TLR4/MD2 in a total internal reflection fluorescence (TIRF) microscope for a single molecule fluorescence analysis. These analyses reveal longitudinal LBP binding to the surface of LPS micelles and multi-round binding/unbinding of CD14 to single LBP/LPS micelles via key charged residues on LBP and CD14. Finally, we reveal that a single LPS molecule bound to CD14 is transferred to TLR4/MD2 in a TLR4-dependent manner. These discoveries, which clarify the molecular mechanism of dynamic LPS transfer to TLR4/MD2 via LBP and CD14, provide novel insights into the initiation of innate immune responses. [BMB Reports 2017; 50(2): 55-57].
authors.affiliation: Graduate School of Medical Science & Engineering, KAIST, Daejeon 34141, Korea.
authors.forename: Soo Jin
authors.initials: SJ
authors.lastname: Kim
authors.affiliation: Graduate School of Medical Science & Engineering, KAIST, Daejeon 34141, Korea.
authors.forename: Ho Min
authors.initials: HM
authors.lastname: Kim
mesh_terms: D000209:Acute-Phase Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D007113:Immunity, Innate; D018950:Lipopolysaccharide Receptors / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D008070:Lipopolysaccharides / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D051218:Lymphocyte Antigen 96 / Q000737:chemistry / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D015398:Signal Transduction / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000737:chemistry / Q000378:metabolism*; D000099231:Lipopolysaccharide-Binding Protein
chemical_list: D000209:Acute-Phase Proteins; D002352:Carrier Proteins; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D051218:Lymphocyte Antigen 96; D008562:Membrane Glycoproteins; D046912:Multiprotein Complexes; D051197:Toll-Like Receptor 4; D000099231:Lipopolysaccharide-Binding Protein; C495377:LY96 protein, human; C495345:TLR4 protein, human