Mechanisms of Signal Transduction
The Triacylated ATP Binding Cluster Transporter Substrate-binding Lipoprotein of Staphylococcus aureus Functions as a Native Ligand for Toll-like Receptor 2*

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Some synthetic lipopeptides, in addition to native lipoproteins derived from both Gram-negative bacteria and mycoplasmas, are known to activate TLR2 (Toll-like receptor 2). However, the native lipoproteins inherent to Gram-positive bacteria, which function as TLR2 ligands, have not been characterized. Here, we have purified a native lipoprotein to homogeneity from Staphylococcus aureus to study as a native TLR2 ligand. The purified 33-kDa lipoprotein was capable of stimulating TLR2 and was identified as a triacylated SitC lipoprotein, which belongs to a family of ATP binding cluster (ABC) transporter substrate-binding proteins. Analyses of the SitC-mediated production of cytokine using mouse peritoneal macrophages revealed that the SitC protein (3 nm) induced the production of tumor necrosis factor-α and interleukin-6. Moreover, analysis of knock-out mice showed that SitC required TLR2 and MyD88, but not TLR1 or TLR6, for the induction of cytokines. In addition to the S. aureus SitC lipoprotein, we purified two other native ABC transporter substrate-binding lipoproteins from Bacillus subtilis and Micrococcus luteus, which were both shown to stimulate TLR2. These results demonstrate that S. aureus SitC lipoprotein is triacylated and that the ABC transporter substrate-binding lipoproteins of Gram-positive bacteria function as native ligands for TLR2.

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The abbreviations used are: TLR, Toll-like receptor; PGN, peptidoglycan; LTA, lipoteichoic acid(s); Pam3CSK4, N-palmitoyl-S-[2,3-bis-(palmitoyloxy)-propyl]-(R)-cysteinyl-(lysyl)3-lysine; ABC, ATP binding cluster; CHO, Chinese hamster ovary; MS, mass spectrometry; MALDI, matrix-assisted laser desorption/ionization; TOF, time-of-flight.

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This work was supported by National Research Laboratory Grants M10400000028-04J0000-02 and MOST/KOSEF Bioscience Grant 20080576001. This work was also partially supported by the BK21 program. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement”in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Table S1 and Figs. S1 and S2.

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Recipient of the Uehara Memorial Foundation Grant.