Department of Biochemistry, University of Zurich, Zurich, Switzerland.
Elife. 2024 Jun 18;13:RP96138. doi: 10.7554/eLife.96138.
The CALHM proteins constitute a family of large pore channels that contains six closely related paralogs in humans. Two family members, CALHM1 and 3, have been associated with the release of ATP during taste sensation. Both proteins form heteromeric channels that activate at positive potential and decreased extracellular Ca concentration. Although the structures of several family members displayed large oligomeric organizations of different size, their function has in most cases remained elusive. Our previous study has identified the paralogs CALHM2, 4 and, 6 to be highly expressed in the placenta and defined their structural properties as membrane proteins exhibiting features of large pore channels with unknown activation properties (Drożdżyk et al., 2020). Here, we investigated whether these placental paralogs would form heteromers and characterized heteromeric complexes consisting of CALHM2 and CALHM4 subunits using specific binders as fiducial markers. Both proteins assemble with different stoichiometries with the largest population containing CALHM2 as the predominant component. In these oligomers, the subunits segregate and reside in their preferred conformation found in homomeric channels. Our study has thus revealed the properties that govern the formation of CALHM heteromers in a process of potential relevance in a cellular context.
CALHM 蛋白构成一个大家族，包含人类中六个密切相关的同源物。家族中的两个成员，CALHM1 和 3，与味觉感知过程中 ATP 的释放有关。这两种蛋白形成异源二聚体通道，在正电势和降低的细胞外 Ca 浓度下激活。尽管几个家族成员的结构显示出不同大小的大型寡聚体组织，但它们的功能在大多数情况下仍然难以捉摸。我们之前的研究已经确定了同源物 CALHM2、4 和 6 在胎盘组织中高度表达，并将其结构特性定义为具有未知激活特性的膜蛋白，表现为大孔通道的特征（Drożdżyk 等人，2020 年）。在这里，我们研究了这些胎盘同源物是否会形成异源二聚体，并使用特异性结合物作为基准标记来表征由 CALHM2 和 CALHM4 亚基组成的异源二聚体复合物。这两种蛋白以不同的化学计量比组装，最大的群体含有作为主要成分的 CALHM2。在这些寡聚体中，亚基分离并存在于其在同源通道中发现的首选构象中。因此，我们的研究揭示了在细胞环境中具有潜在相关性的过程中形成 CALHM 异源二聚体的性质。
