Taskinen Barbara, Ferrada Evandro, Fowler Douglas M
From the Department of Genome Sciences, University of Washington, Seattle, Washington 98195-5065 and.
From the Department of Genome Sciences, University of Washington, Seattle, Washington 98195-5065 and
J Biol Chem. 2017 Nov 10;292(45):18518-18529. doi: 10.1074/jbc.M117.811174. Epub 2017 Sep 22.
Stringent regulation of tyrosine kinase activity is essential for normal cellular function. In humans, the tyrosine kinase Src is inhibited via phosphorylation of its C-terminal tail by another kinase, C-terminal Src kinase (Csk). Although Src and Csk orthologs are present across holozoan organisms, including animals and protists, the Csk-Src negative regulatory mechanism appears to have evolved gradually. For example, in choanoflagellates, Src and Csk are both active, but the negative regulatory mechanism is reportedly absent. In filastereans, a protist clade closely related to choanoflagellates, Src is active, but Csk is apparently inactive. In this study, we use a combination of bioinformatics, kinase assays, and yeast-based growth assays to characterize holozoan Src and Csk orthologs. We show that, despite appreciable differences in domain architecture, Csk from , a highly diverged holozoan marine protist, is active and can inhibit Src. However, in comparison with other Csk orthologs, Csk displays broad substrate specificity and inhibits Src in an activity-independent manner. Furthermore, in contrast to previous studies, we show that Csk from the filasterean is active and that the Csk-Src negative regulatory mechanism is present in Csk and Src proteins from and the choanoflagellate Our results suggest that negative regulation of Src by Csk is more ancient than previously thought and that it might be conserved across all holozoan species.
酪氨酸激酶活性的严格调控对于正常细胞功能至关重要。在人类中，酪氨酸激酶Src通过另一种激酶——C末端Src激酶（Csk）对其C末端尾巴的磷酸化作用而受到抑制。尽管Src和Csk的直系同源物存在于包括动物和原生生物在内的所有全动物界生物中，但Csk-Src负调控机制似乎是逐渐进化而来的。例如，在领鞭毛虫中，Src和Csk都是活跃的，但据报道不存在负调控机制。在丝足虫中，这是一种与领鞭毛虫密切相关的原生生物类群，Src是活跃的，但Csk显然是不活跃的。在本研究中，我们结合生物信息学、激酶分析和基于酵母的生长分析来表征全动物界的Src和Csk直系同源物。我们发现，尽管结构域结构存在明显差异，但来自一种高度分化的全动物界海洋原生生物的Csk是活跃的，并且能够抑制Src。然而，与其他Csk直系同源物相比，该Csk表现出广泛的底物特异性，并且以一种不依赖活性的方式抑制Src。此外，与先前的研究相反，我们发现丝足虫的Csk是活跃的，并且Csk-Src负调控机制存在于丝足虫、领鞭毛虫的Csk和Src蛋白中。我们的结果表明，Csk对Src的负调控比之前认为的更为古老，并且可能在所有全动物界物种中都保守存在。
