Matsuda Tadashi, Feng Jian, Witthuhn Bruce A, Sekine Yuichi, Ihle James N
Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
Biochem Biophys Res Commun. 2004 Dec 10;325(2):586-94. doi: 10.1016/j.bbrc.2004.10.071.
Janus kinases are the key enzymes involved in the initial transmission of signals in response to type I and II cytokines. Activation of the signal begins with the transphosphorylation of Jak kinases. Substrates that give rise to downstream events are recruited to the receptor complex in part by interactions with phosphorylated tyrosines. The identity of many of the phosphotyrosines responsible for recruitment has been elucidated as being receptor-based tyrosines. The ability of Jaks to recruit substrates through their own phosphotyrosines has been demonstrated for tyrosines in the kinase activation loop. Recent studies demonstrate that other tyrosines have implications in regulatory roles of Jak kinase activity. In this study, baculovirus-produced Jak2 was utilized to demonstrate that transphosphorylation of Jak kinases occurs on multiple residues throughout the protein. We demonstrate that among the tyrosines phosphorylated, those in the kinase domain occur as expected, but many other sites are also phosphorylated. The tyrosines conserved in the Jak family are the object of this study, although many of them are phosphorylated, many are not. This result suggests that conservation of tyrosines is perhaps as important in maintaining structure of the Jak family. Additionally, non-Jak family conserved tyrosines are phosphorylated suggesting that the individual Jaks ability to phosphorylated specific tyrosines may influence signals emitting from activated Jaks.
Janus激酶是参与I型和II型细胞因子信号初始传递的关键酶。信号的激活始于Jak激酶的转磷酸化。引发下游事件的底物部分通过与磷酸化酪氨酸的相互作用被招募到受体复合物中。许多负责招募的磷酸酪氨酸已被阐明为基于受体的酪氨酸。Jak激酶通过自身磷酸酪氨酸招募底物的能力已在激酶激活环中的酪氨酸上得到证实。最近的研究表明，其他酪氨酸对Jak激酶活性的调节作用也有影响。在本研究中，利用杆状病毒产生的Jak2来证明Jak激酶的转磷酸化发生在整个蛋白质的多个残基上。我们证明，在磷酸化的酪氨酸中，激酶结构域中的酪氨酸如预期出现，但许多其他位点也被磷酸化。Jak家族中保守的酪氨酸是本研究的对象，尽管其中许多被磷酸化，但也有许多没有。这一结果表明，酪氨酸的保守性在维持Jak家族结构方面可能同样重要。此外，非Jak家族保守的酪氨酸也被磷酸化，这表明Jak激酶磷酸化特定酪氨酸的个体能力可能会影响激活的Jak发出的信号。
