title: Human TLR4 polymorphism D299G/T399I alters TLR4/MD-2 conformation and response to a weak ligand monophosphoryl lipid A.
abstract: A cell surface heterodimer Toll-like receptor 4 (TLR4)/MD-2 senses lipopolysaccharide (LPS), a principal membrane component of Gram-negative bacteria. LPS binds to MD-2 and induces dimerization of TLR4/MD-2. Dimerized TLR4 activates downstream signaling. TLR4 polymorphism replacing Asp299 with Gly and Thr399 with Ile (D299G/T399I) causes LPS hyporesponsiveness, and is associated with a variety of infectious and noninfectious diseases. However, a molecular mechanism underlying the LPS hyporesponsiveness remains controversial. We here asked whether the TLR4 polymorphism influenced cell surface expression of TLR4/MD-2, ligand-dependent TLR4/MD-2 dimerization or TLR4/MD-2 responses to a weak agonist monophosphoryl lipid A (MPL). A newly established anti-TLR4 mAb detected D299G/T399I TLR4/MD-2 on Ba/F3 cells, whereas a previous anti-TLR4 mAb did will this fit on the line above?, suggesting that the D299G/T399I polymorphism caused a conformational change in TLR4. Hyporesponsiveness of D299G/T399I TLR4/MD-2 was much more apparent when cells were stimulated with MPL than with lipid A. MPL-dependent TLR4/MD-2 dimerization was impaired by the D299G/T399I polymorphism. The D299G/T399I polymorphism did not alter LPS-binding to soluble TLR4/MD-2, but impaired its dimerization. These results suggest that the D299G/T399I TLR4 polymorphism impairs TLR4/MD-2 responses by altering ligand-dependent dimerization.
authors.affiliation: Division of Innate Immunity, The Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Tokyo 108-8639, Japan.
authors.forename: Natsuko
authors.initials: N
authors.lastname: Yamakawa
authors.forename: Umeharu
authors.initials: U
authors.lastname: Ohto
authors.forename: Sachiko
authors.initials: S
authors.lastname: Akashi-Takamura
authors.forename: Koichiro
authors.initials: K
authors.lastname: Takahashi
authors.forename: Shin-Ichiroh
authors.initials: S
authors.lastname: Saitoh
authors.forename: Natsuko
authors.initials: N
authors.lastname: Tanimura
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Suganami
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ogawa
authors.forename: Takuma
authors.initials: T
authors.lastname: Shibata
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Shimizu
authors.forename: Kensuke
authors.initials: K
authors.lastname: Miyake
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001402:B-Lymphocytes / Q000166:cytology / Q000187:drug effects* / Q000276:immunology; D002461:Cell Line, Transformed; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D017930:Genes, Reporter; D006801:Humans; D008050:Lipid A / Q000031:analogs & derivatives* / Q000494:pharmacology; D008156:Luciferases; D051218:Lymphocyte Antigen 96 / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D051379:Mice; D011110:Polymorphism, Genetic; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization / Q000187:drug effects / Q000276:immunology; D015398:Signal Transduction / Q000187:drug effects; D051197:Toll-Like Receptor 4 / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; C495377:LY96 protein, human; D008050:Lipid A; D051218:Lymphocyte Antigen 96; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D008156:Luciferases; C048436:monophosphoryl lipid A