Seitz Markus, Maillard Ludovic T, Obrecht Daniel, Robinson John A
Department of Chemistry, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
Chembiochem. 2008 May 23;9(8):1318-22. doi: 10.1002/cbic.200700773.
Many protein-protein interactions involved in cell signalling, cell adhesion and regulation of transcription are mediated by short alpha-helical recognition motifs with the sequence Leu-Xaa-Xaa-Leu-Leu (LXXLL, where Xaa is any amino acid). Originally observed in cofactors that interact with hormone-activated nuclear receptors, LXXLL motifs are now known to occur in many transcription factors, including the STAT family, which transmit signals from activated cytokine receptors at the cell surface to target genes in the nucleus. STAT 6 becomes activated in response to IL-4 and IL-13, which regulate immune and anti-inflammatory responses. Structural studies have revealed how an LXXLL motif located in 2.5 turns of an alpha-helical peptide derived from STAT 6 provide contacts through the leucine side chains to the coactivator of transcription, NCoA-1. However, since many protein-protein interactions are mediated by LXXLL motifs, it is important to understand how specificity is achieved in this and other signalling pathways. Here, we show that energetically important contacts between STAT 6 and NCoA-1 are made in residues that flank the LXXLL motif, including the underlined residues in the sequence LLPPTEQDLTKLL. We also demonstrate how the affinity for NCoA-1 of peptides derived from this region of STAT 6 can be significantly improved by optimising knobs-into-holes contacts on the surface of the protein. The results provide important new insights into the origins of binding specificity, and might be of practical value in the design of novel small-molecule inhibitors of this important protein-protein interaction.
许多参与细胞信号传导、细胞黏附和转录调控的蛋白质-蛋白质相互作用是由具有Leu-Xaa-Xaa-Leu-Leu（LXXLL，其中Xaa为任意氨基酸）序列的短α-螺旋识别基序介导的。LXXLL基序最初在与激素激活的核受体相互作用的辅因子中被观察到，现在已知它存在于许多转录因子中，包括STAT家族，该家族将细胞表面激活的细胞因子受体发出的信号传递到细胞核中的靶基因。STAT 6在白细胞介素-4（IL-4）和白细胞介素-13的作用下被激活，这两种细胞因子调节免疫和抗炎反应。结构研究揭示了源自STAT 6的α-螺旋肽2.5圈中的LXXLL基序如何通过亮氨酸侧链与转录共激活因子NCoA-1形成接触。然而，由于许多蛋白质-蛋白质相互作用是由LXXLL基序介导的，了解在这一信号通路和其他信号通路中如何实现特异性非常重要。在这里，我们表明STAT 6和NCoA-1之间在能量上重要的接触是在LXXLL基序侧翼的残基中形成的，包括序列LLPPTEQDLTKLL中带下划线的残基。我们还证明了通过优化蛋白质表面的旋钮-孔接触，可以显著提高源自STAT 6这一区域的肽对NCoA-1的亲和力。这些结果为结合特异性的起源提供了重要的新见解，并且可能在设计这种重要的蛋白质-蛋白质相互作用的新型小分子抑制剂方面具有实际价值。
