Cell surface receptors must specifically recognize an extracellular ligand and then trigger an appropriate response within the cell. Their general structure enables this, as it comprises an extracellular domain that can bind an extracellular ligand, a cytoplasmic domain that can transduce a signal inside the cell to produce an appropriate response, and a transmembrane domain that links the two and is responsible for accurately delivering specific information on a binding event from the extracellular domain to the cytoplasmic domain, to trigger the proper response. A vast body of research has focused on elucidating the specific mechanisms responsible for regulating extracellular binding events and the subsequent interactions of the cytoplasmic domain with intracellular signaling. In contrast, far less work has focused on examining how the transmembrane domain links these domains and delivers the necessary information. In this review, we propose the importance of the transmembrane domain as a signal regulator. We highlight the cell adhesion receptor, syndecan, as a special case, and propose that the transmembrane domain-mediated oligomerization of the syndecan cytoplasmic domain is a unique regulatory mechanism in syndecan signaling.

细胞表面受体必须特异性识别细胞外配体，然后触发细胞内的适当反应。它们的一般结构使之成为可能，因为它包含可以结合细胞外配体的细胞外结构域，可以转导细胞内信号以产生适当应答的细胞质结构域，以及将两者连接并负责准确递送的跨膜结构域。有关从细胞外结构域到胞质结构域的结合事件的特定信息，以触发适当的响应。大量的研究集中在阐明负责调节细胞外结合事件以及随后胞质域与细胞内信号传导相互作用的特定机制上。相比之下，很少有工作专注于检查跨膜域如何链接这些域并传递必要的信息。在这篇综述中，我们提出跨膜结构域作为信号调节剂的重要性。我们强调细胞粘附受体，syndecan，作为一个特例，并提出跨膜结构域介导的syndecan胞质域的寡聚化是syndecan信号传导中的独特调控机制。