The spatial distribution of proteins in cell membranes is crucial for signal transduction, cell communication and membrane trafficking. Members of the Tetraspanin family organize functional protein clusters within the plasma membrane into so-called Tetraspanin-enriched microdomains (TEMs). Direct interactions between Tetraspanins are believed to be important for this organization. However, studies thus far have utilized mainly co-immunoprecipitation methods that cannot distinguish between direct and indirect, through common partners, interactions. Here we study Tetraspanin 8 homointeractions in living cells via quantitative fluorescence microscopy. We demonstrate that Tetraspanin 8 exists in a monomer-dimer equilibrium in the plasma membrane. Tetraspanin 8 dimerization is described by a high dissociation constant (Kd = 14 700 ± 1100 Tspan8/µm2), one of the highest dissociation constants measured for membrane proteins in live cells. We propose that this high dissociation constant, and thus the short lifetime of the Tetraspanin 8 dimer, is critical for Tetraspanin 8 functioning as a master regulator of cell signaling.

中文翻译：

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质膜中四跨膜蛋白 8 同源相互作用的定量表征

蛋白质在细胞膜中的空间分布对于信号转导、细胞通讯和膜运输至关重要。Tetraspanin 家族的成员将质膜内的功能性蛋白质簇组织成所谓的富含 Tetraspanin 的微区 (TEM)。Tetraspanins 之间的直接相互作用被认为对这个组织很重要。然而，迄今为止的研究主要利用共免疫沉淀方法，无法通过共同伙伴、相互作用区分直接和间接。在这里，我们通过定量荧光显微镜研究活细胞中的 Tetraspanin 8 同源相互作用。我们证明 Tetraspanin 8 存在于质膜中的单体-二聚体平衡中。四跨膜蛋白 8 二聚化由高解离常数 (Kd = 14 700 ± 1100 Tspan8/µm2) 描述，为活细胞中的膜蛋白测量的最高解离常数之一。我们认为这种高解离常数以及 Tetraspanin 8 二聚体的短寿命对于 Tetraspanin 8 作为细胞信号传导的主调节器发挥作用至关重要。