CD14 directly binds to triacylated lipopeptides and facilitates recognition of the lipopeptides by the receptor complex of Toll-like receptors 2 and 1 without binding to the complex
Article first published online: 11 JUL 2006
Volume 8, Issue 12, pages 1899–1909, December 2006
How to Cite
Nakata, T., Yasuda, M., Fujita, M., Kataoka, H., Kiura, K., Sano, H. and Shibata, K. (2006), CD14 directly binds to triacylated lipopeptides and facilitates recognition of the lipopeptides by the receptor complex of Toll-like receptors 2 and 1 without binding to the complex. Cellular Microbiology, 8: 1899–1909. doi: 10.1111/j.1462-5822.2006.00756.x
- Issue published online: 11 JUL 2006
- Article first published online: 11 JUL 2006
- Received 22 March, 2006; revised 12 May, 2006; accepted 14 May, 2006.
It has demonstrated that the recognition of triacylated lipopeptides by Toll-like receptor (TLR) 2 requires TLR1 as a coreceptor. In the NF-κB reporter assay system in which human embryonic kidney 293 cells were transfected with TLR2 and TLR1 together with an NF-κB luciferase reporter gene, S-(2,3-bispalmitoyloxypropyl)-N-palmitoyl-Cys-Lys-Lys-Lys-Lys (Pam3CSK4) and Pam3CSSNA were recognized by TLR2/TLR1, but the recognition level was unexpectedly very low. However, cotransfection of CD14 drastically enhanced the recognition of triacylated lipopeptides by TLR2/TLR1. The CD14-induced enhancement did not occur without cotransfection of TLR1. Both CD14dS39-A48, a mutant with deletion of the part of possible N-terminal ligand-binding pocket, and anti-CD14 monoclonal antibody reduced the CD14-induced enhancement. Transfection of a TIR domain-deficient mutant of TLR2 (TLR2dE772-S784) or TLR1 (TLR1dQ636-K779) completely abrogated the CD14-induced enhancement. Soluble recombinant CD14 added extracellularly enhanced the recognition of Pam3CSSNA by TLR2/TLR1. Immunoprecipitation analysis demonstrated that CD14 was not associated with TLR2 but that TLR1 was associated with TLR2. In addition, surface plasmon resonance-based assay demonstrated that CD14 binds to Pam3CSK4 at a dissociation constant of 5.7 µM. This study suggests that CD14 directly binds to triacylated lipopeptides and facilitates recognition of the lipopeptides by the TLR2/TLR1 complex without binding to the receptor complex.