Haan Serge, Margue Christiane, Engrand Arnaud, Rolvering Catherine, Schmitz-Van de Leur Hildegard, Heinrich Peter C, Behrmann Iris, Haan Claude
Life Science Research Unit, Faculté des Sciences, de la Technologie et de la Communication, Université du Luxembourg, Luxembourg.
J Immunol. 2008 Jan 15;180(2):998-1007. doi: 10.4049/jimmunol.180.2.998.
Jak1 is a tyrosine kinase that noncovalently forms tight complexes with a variety of cytokine receptors and is critically involved in signal transduction via cytokines. Jaks are predicted to have a 4.1, ezrin, radixin, moesin (FERM) domain at their N terminus. FERM domains are composed of three structurally unrelated subdomains (F1, F2, and F3) which are in close contact to one another and form the clover-shaped FERM domain. We generated a model structure of the Jak1 FERM domain, based on solved FERM structures and the alignments with other FERM domains. To destabilize different subdomains and to uncover their exact function, we mutated specific hydrophobic residues conserved in FERM domains and involved in hydrophobic core interactions. In this study, we show that the structural integrity of the F2 subdomain of the FERM domain of Jak1 is necessary to bind the IFN-gammaRalpha. By mutagenesis of hydrophobic residues in the hydrophobic core between the three FERM subdomains, we find that the structural context of the FERM domain is necessary for the inhibition of Jak1 phosphorylation. Thus, FERM domain mutations can have repercussions on Jak1 function. Interestingly, a mutation in the kinase domain (Jak1-K907E), known to abolish the catalytic activity, also leads to an impaired binding to the IFN-gammaRalpha when this mutant is expressed at endogenous levels in U4C cells. Our data show that the structural integrity of both the FERM domain and of the kinase domain is essential for both receptor binding and catalytic function/autoinhibition.
Jak1是一种酪氨酸激酶，它与多种细胞因子受体非共价形成紧密复合物，并在通过细胞因子进行的信号转导中起关键作用。预计Jaks在其N端具有一个4.1、埃兹蛋白、根蛋白、膜突蛋白（FERM）结构域。FERM结构域由三个结构不相关的亚结构域（F1、F2和F3）组成，它们彼此紧密接触并形成三叶草形的FERM结构域。我们基于已解析的FERM结构以及与其他FERM结构域的比对，生成了Jak1 FERM结构域的模型结构。为了破坏不同亚结构域的稳定性并揭示其确切功能，我们对FERM结构域中保守且参与疏水核心相互作用的特定疏水残基进行了突变。在本研究中，我们表明Jak1的FERM结构域的F2亚结构域的结构完整性对于结合IFN-γRα是必要的。通过对三个FERM亚结构域之间疏水核心中的疏水残基进行诱变，我们发现FERM结构域的结构背景对于抑制Jak1磷酸化是必要的。因此，FERM结构域突变可能会对Jak1功能产生影响。有趣的是，已知能消除催化活性的激酶结构域中的一个突变（Jak1-K907E），当该突变体在U4C细胞中以内源水平表达时，也会导致与IFN-γRα的结合受损。我们的数据表明，FERM结构域和激酶结构域的结构完整性对于受体结合以及催化功能/自身抑制都是必不可少的。
