Institute of Physical and Theoretical Chemistry, Goethe University, Max von Laue Straße 7, 60438 Frankfurt/Main, Germany.
Stem Cell Biology and Regenerative Medicine, School of Pharmacy, University of Reading, Hopkins Building, Whiteknights, Reading RG6 6UB, UK.
Sci Signal. 2017 Oct 31;10(503):eaan1308. doi: 10.1126/scisignal.aan1308.
In humans, invading pathogens are recognized by Toll-like receptors (TLRs). Upon recognition of lipopolysaccharide (LPS) derived from the cell wall of Gram-negative bacteria, TLR4 dimerizes and can stimulate two different signaling pathways, the proinflammatory, MyD88-dependent pathway and the antiviral, MyD88-independent pathway. The balance between these two pathways is ligand-dependent, and ligand composition determines whether the invading pathogen activates or evades the host immune response. We investigated the dimerization behavior of TLR4 in intact cells in response to different LPS chemotypes through quantitative single-molecule localization microscopy. Quantitative superresolved data showed that TLR4 was monomeric in the absence of its co-receptors MD2 and CD14 in transfected HEK 293 cells. When TLR4 was present together with MD2 and CD14 but in the absence of LPS, 52% of the receptors were monomeric and 48% were dimeric. LPS from or caused the formation of dimeric TLR4 complexes, whereas the antagonistic LPS chemotype from maintained TLR4 in monomeric form at the cell surface. Furthermore, we showed that LPS-dependent dimerization was required for the activation of NF-κB signaling. Together, these data demonstrate ligand-dependent dimerization of TLR4 in the cellular environment, which could pave the way for a molecular understanding of biased signaling downstream of the receptor.
在人类中，入侵病原体被 Toll 样受体 (TLR) 识别。在识别来自革兰氏阴性菌细胞壁的脂多糖 (LPS) 后，TLR4 二聚化，并能刺激两种不同的信号通路，促炎的 MyD88 依赖性通路和抗病毒的 MyD88 非依赖性通路。这两条通路之间的平衡是配体依赖性的，配体组成决定了入侵病原体是激活还是逃避宿主免疫反应。我们通过定量单分子定位显微镜研究了 TLR4 在完整细胞中对不同 LPS 化学型的二聚化行为。定量超分辨数据显示，在转染的 HEK 293 细胞中，没有其共受体 MD2 和 CD14 时，TLR4 是单体的。当 TLR4 与 MD2 和 CD14 一起存在但没有 LPS 时，52%的受体是单体，48%是二聚体。来自 或 的 LPS 导致 TLR4 二聚体复合物的形成，而来自 的拮抗 LPS 化学型在细胞表面将 TLR4 保持为单体形式。此外，我们表明 LPS 依赖性二聚化是 NF-κB 信号激活所必需的。总之，这些数据表明 TLR4 在细胞环境中的配体依赖性二聚化，这可能为受体下游偏向信号的分子理解铺平道路。
