Protein Signaling Domains Laboratory, Department of Biological Sciences, Biocomplexity Institute, and Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg VA, 24061, USA.
School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, P. R. China.
Sci Rep. 2017 Feb 22;7:43043. doi: 10.1038/srep43043.
Pathogen-activated Toll-like receptors (TLRs), such as TLR2 and TLR4, dimerize and move laterally across the plasma membrane to phosphatidylinositol (4,5)-bisphosphate-enriched domains. At these sites, TLRs interact with the TIR domain-containing adaptor protein (TIRAP), triggering a signaling cascade that leads to innate immune responses. Membrane recruitment of TIRAP is mediated by its phosphoinositide (PI)-binding motif (PBM). We show that TIRAP PBM transitions from a disordered to a helical conformation in the presence of either zwitterionic micelles or monodispersed PIs. TIRAP PBM bound PIs through basic and nonpolar residues with high affinity, favoring a more ordered structure. TIRAP is phosphorylated at Thr28 within its PBM, which leads to its ubiquitination and degradation. We demonstrate that phosphorylation distorts the helical structure of TIRAP PBM, reducing PI interactions and cell membrane targeting. Our study provides the basis for TIRAP membrane insertion and the mechanism by which it is removed from membranes to avoid sustained innate immune responses.
病原体激活的 Toll 样受体（TLR），如 TLR2 和 TLR4，二聚化并横向穿过质膜移动到富含磷脂酰肌醇（4,5）-二磷酸的区域。在这些部位，TLR 与含 TIR 结构域的衔接蛋白（TIRAP）相互作用，触发导致先天免疫反应的信号级联反应。TIRAP 的膜募集由其磷酸肌醇（PI）结合基序（PBM）介导。我们表明，TIRAP PBM 在存在两性离子胶束或单分散 PI 的情况下从无规卷曲构象转变为螺旋构象。TIRAP PBM 通过碱性和非极性残基与 PI 高亲和力结合，有利于更有序的结构。TIRAP 在其 PBM 内的 Thr28 处发生磷酸化，导致其泛素化和降解。我们证明磷酸化扭曲了 TIRAP PBM 的螺旋结构，减少了 PI 相互作用和质膜靶向。我们的研究为 TIRAP 膜插入提供了基础，并解释了其从膜中去除以避免持续的先天免疫反应的机制。
