TLR1- and TLR6-independent Recognition of Bacterial Lipopeptides

Ute Buwitt-Beckmann,Holger Heine,Karl-Heinz Wiesmüller,Günther Jung,Roland Brock,Shizuo Akira,Artur J Ulmer

doi:10.1074/jbc.m512525200

Abstract

Bacterial cell walls contain lipoproteins/peptides, which are strong modulators of the innate immune system. Triacylated lipopeptides are assumed to be recognized by TLR2/TLR1-, whereas diacylated lipopeptides use TLR2/TLR6 heteromers for signaling. Following our initial discovery of TLR6-independent diacylated lipopeptides, we could now characterize di- and triacylated lipopeptides (e.g. Pam(2)C-SK(4), Pam(3)C-GNNDESNISFKEK), which have stimulatory activity in TLR1- and in TLR6-deficient mice. Furthermore, for the first time, we present triacylated lipopeptides with short length ester-bound fatty acids (like PamOct(2)C-SSNASK(4)), which induce no response in TLR1-deficient cells. No differences in the phosphorylation of MAP kinases by lipopeptide analogs having different TLR2-coreceptor usage were observed. Blocking experiments indicated that different TLR2 heteromers recognize their specific lipopeptide ligands independently from each other. In summary, a triacylation pattern is necessary but not sufficient to render a lipopeptide TLR1-dependent, and a diacylation pattern is necessary but not sufficient to render a lipopeptide TLR6-dependent. Contrary to the current model, distinct lipopeptides are recognized by TLR2 in a TLR1- and TLR6-independent manner.

Highlights

Rides (LPS), and oligonucleotides [2]
Based on the assumption that TLR2 signals only as a heteromer in association with either TLR6 or TLR1, we hypothesized that these lipopeptides instead utilize TLR1 as the coreceptor and should not activate cells derived from TLR1-deficient mice
Spleen cells from wild-type mice and TLR1- or TLR6-deficient mice were stimulated with these lipopeptides

Summary

Introduction

Rides (LPS), and oligonucleotides (double-stranded RNA, single-stranded RNA, and DNA) [2]. The diacylated MALP2 requires TLR2 and TLR6 for signaling, whereas the triacylated synthetic lipohexapeptide Pam3C-SK4 is able to induce activation of innate immune cells independently of TLR6 [17,18,19,20]. Our investigations led to LP with ester-bound short chain length fatty acids, which do not induce signaling in TLR1-deficient mice.

Results

Conclusion