Corbalan-Garcia S, Margarit S M, Galron D, Yang S S, Bar-Sagi D
Department of Molecular Genetics and Microbiology, State University of New York at Stony Brook, 11794-8621, USA.
Mol Cell Biol. 1998 Feb;18(2):880-6. doi: 10.1128/MCB.18.2.880.
The guanine nucleotide exchange factor Sos mediates the coupling of receptor tyrosine kinases to Ras activation. To investigate the mechanisms that control Sos activity, we have analyzed the contribution of various domains to its catalytic activity. Using human Sos1 (hSos1) truncation mutants, we show that Sos proteins lacking either the amino or the carboxyl terminus domain, or both, display a guanine nucleotide exchange activity that is significantly higher compared with that of the full-length protein. These results demonstrate that both the amino and the carboxyl terminus domains of Sos are involved in the negative regulation of its catalytic activity. Furthermore, in vitro Ras binding experiments suggest that the amino and carboxyl terminus domains exert negative allosteric control on the interaction of the Sos catalytic domain with Ras. The guanine nucleotide exchange activity of hSos1 was not augmented by growth factor stimulation, indicating that Sos activity is constitutively maintained in a downregulated state. Deletion of both the amino and the carboxyl terminus domains was sufficient to activate the transforming potential of Sos. These findings suggest a novel negative regulatory role for the amino terminus domain of Sos and indicate a cooperation between the amino and the carboxyl terminus domains in the regulation of Sos activity.
鸟嘌呤核苷酸交换因子Sos介导受体酪氨酸激酶与Ras激活的偶联。为了研究控制Sos活性的机制，我们分析了各个结构域对其催化活性的贡献。使用人Sos1（hSos1）截短突变体，我们发现缺失氨基或羧基末端结构域或两者的Sos蛋白显示出与全长蛋白相比显著更高的鸟嘌呤核苷酸交换活性。这些结果表明，Sos的氨基和羧基末端结构域均参与其催化活性的负调控。此外，体外Ras结合实验表明，氨基和羧基末端结构域对Sos催化结构域与Ras的相互作用施加负别构控制。hSos1的鸟嘌呤核苷酸交换活性未因生长因子刺激而增强，表明Sos活性在下调状态下持续维持。缺失氨基和羧基末端结构域足以激活Sos的转化潜能。这些发现提示了Sos氨基末端结构域的一种新的负调控作用，并表明氨基和羧基末端结构域在Sos活性调控中存在协同作用。
