Trk-A is a receptor tyrosine kinase (RTK) which plays an essential role in the development and functioning of the nervous system. Trk-A is expressed in neurons and signals in response to two ligands, NGF and NT-3, with very different functional consequences. Thus, NGF and NT-3 are "biased" ligands for Trk-A. Since it has been hypothesized that biased RTK ligands induce differential stabilization of RTK dimers, here we seek to test this hypothesis for NGF and NT-3. In particular, we use Förster Resonance Energy Transfer (FRET) and Fluorescence Intensity Fluctuation (FIF) spectroscopy to assess the strength of Trk-A interactions and Trk-A oligomer size in the presence of the two ligands. While the difference in Trk-A behavior in response to the two ligands has been previously attributed to differences in their binding to Trk-A in the endosomes at low pH, here we further show differences in the stabilities of the NGF and NT-3 bound Trk-A dimers in the plasma membrane and at neutral pH. We discuss the biological significance of these new findings and their implications for the design of Trk-A ligands with novel functionalities.

中文翻译：

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偏向配体 NGF 和 NT-3 差异稳定 Trk-A 二聚体

Trk-A 是一种受体酪氨酸激酶 (RTK)，在神经系统的发育和功能中起重要作用。Trk-A 在神经元中表达，并响应两种配体 NGF 和 NT-3 发出信号，具有非常不同的功能后果。因此，NGF 和 NT-3 是 Trk-A 的“偏向”配体。由于已经假设偏向的 RTK 配体诱导 RTK 二聚体的差异稳定化，因此我们在此试图检验 NGF 和 NT-3 的这一假设。特别是，我们使用 Förster 共振能量转移 (FRET) 和荧光强度波动 (FIF) 光谱来评估两种配体存在下 Trk-A 相互作用的强度和 Trk-A 低聚物的大小。虽然 Trk-A 对两种配体的反应行为的差异先前已归因于它们在低 pH 值下与内体中 Trk-A 结合的差异，但在这里我们进一步显示了 NGF 和 NT-3 结合稳定性的差异质膜中的 Trk-A 二聚体和中性 pH 值。我们讨论了这些新发现的生物学意义及其对设计具有新功能的 Trk-A 配体的影响。