Toll-like receptor 9 binds single-stranded CpG-DNA in a sequence- and pH-dependent manner.
Toll-like receptors (TLR) recognize bacterial and viral components, but direct interaction of receptor and ligand is unclear. Here, we demonstrate that TLR9 binds directly and sequence-specifically to single-stranded unmethylated CpG-DNA containing a phosphodiester backbone. TLR9-CpG-DNA interaction occurs at the acidic pH (6.5-5.0) found in endosomes and lysosomes. By sequence comparison we identified a potential CpG-DNA binding domain homologous to that described for methyl-CpG-DNA binding proteins. Amino acid substitutions in this region abrogated CpG-DNA binding and led to loss of NF-kappaB activation. Furthermore, chloroquine and quinacrine, therapeutic agents for autoimmune diseases like rheumatoid arthritis and systemic lupus erythematosus, directly blocked TLR9-CpG-DNA interaction but not TLR2-Pam3Cys binding. Our results demonstrate direct binding of TLR9 to CpG-DNA and suggest that the therapeutic activity of chloroquine and quinacrine in autoimmune diseases may be due to its activity as a TLR9 antagonist and inhibitor of endosomal acidification.
Rutz
Mark
M
Institute for Medical Microbiology, Hygiene and Immunology, Munich, Germany.
Metzger
Jochen
J
Gellert
Tanja
T
Luppa
Peter
P
Lipford
Grayson B
GB
Wagner
Hermann
H
Bauer
Stefan
S
D000595:Amino Acid Sequence; D001665:Binding Sites; D002460:Cell Line; D002738:Chloroquine / Q000494:pharmacology; D018899:CpG Islands; D004277:DNA, Single-Stranded / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D011796:Quinacrine / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism*; D051195:Toll-Like Receptor 2; D051217:Toll-Like Receptor 9; D051193:Toll-Like Receptors
D004277:DNA, Single-Stranded; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; C495342:TLR2 protein, human; C495371:TLR9 protein, human; D051195:Toll-Like Receptor 2; D051217:Toll-Like Receptor 9; D051193:Toll-Like Receptors; D002738:Chloroquine; D011796:Quinacrine