Lewis Andrew K, Valley Christopher C, Peery Stephen L, Brummel Benjamin, Braun Anthony R, Karim Christine B, Sachs Jonathan N
Department of Biomedical Engineering, University of Minnesota, Twin Cities, Minneapolis, MN 55455, USA.
Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Twin Cities, Minneapolis, MN 55455, USA.
J Mol Biol. 2016 Dec 4;428(24 Pt A):4843-4855. doi: 10.1016/j.jmb.2016.10.001. Epub 2016 Oct 6.
Death receptor 5 (DR5) is an apoptosis-inducing member of the tumor necrosis factor receptor superfamily, whose activity has been linked to membrane cholesterol content. Upon ligand binding, DR5 forms large clusters within the plasma membrane that have often been assumed to be manifestations of receptor co-localization in cholesterol-rich membrane domains. However, we have recently shown that DR5 clusters are more than just randomly aggregated receptors. Instead, these are highly structured networks held together by receptor dimers. These dimers are stabilized by specific transmembrane helix-helix interactions, including a disulfide bond in the long isoform of the receptor. The complex relationships among DR5 network formation, transmembrane helix dimerization, membrane cholesterol, and receptor activity has not been established. It is unknown whether the membrane itself plays an active role in driving DR5 transmembrane helix interactions or in the formation of the networks. We show that cholesterol depletion in cells does not inhibit the formation of DR5 networks. However, the networks that form in cholesterol-depleted cells fail to induce caspase cleavage. These results suggest a potential structural difference between active and inactive networks. As evidence, we show that cholesterol is necessary for the covalent dimerization of DR5 transmembrane domains. Molecular simulations and experiments in synthetic vesicles on the DR5 transmembrane dimer suggest that dimerization is facilitated by increased helicity in a thicker bilayer.
死亡受体5（DR5）是肿瘤坏死因子受体超家族中一种可诱导细胞凋亡的成员，其活性与膜胆固醇含量有关。在配体结合后，DR5在质膜内形成大的簇，人们通常认为这些簇是受体在富含胆固醇的膜结构域中共定位的表现。然而，我们最近发现DR5簇不仅仅是随机聚集的受体。相反，它们是由受体二聚体维系在一起的高度结构化网络。这些二聚体通过特定的跨膜螺旋-螺旋相互作用得以稳定，包括受体长异构体中的一个二硫键。DR5网络形成、跨膜螺旋二聚化、膜胆固醇和受体活性之间的复杂关系尚未明确。尚不清楚膜本身在驱动DR5跨膜螺旋相互作用或网络形成中是否发挥积极作用。我们发现细胞中的胆固醇耗竭并不抑制DR5网络的形成。然而，在胆固醇耗竭的细胞中形成的网络无法诱导半胱天冬酶裂解。这些结果表明活性网络和非活性网络之间可能存在结构差异。作为证据，我们表明胆固醇是DR5跨膜结构域共价二聚化所必需的。对DR5跨膜二聚体进行的分子模拟和在合成囊泡中的实验表明，在较厚的双层膜中螺旋度增加有助于二聚化。
