Thermodynamics of β-catenin-ligand interactions -: The roles of the N- and C-terminal tails in modulating binding affinity
Thermodynamics of β-catenin-ligand interactions -: The roles of the N- and C-terminal tails in modulating binding affinity
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DOI：
10.1074/jbc.m511338200
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发表时间：
2006-01-13
影响因子：
4.8
通讯作者：
Weis, WI
中科院分区：
文献类型：
--
作者：
Choi, HJ;Huber, AH;Weis, WI
β-连环蛋白是粘附连接的结构组分，在粘附连接处，它结合到钙粘蛋白细胞粘附分子的胞质结构域。β-连环蛋白也是Wnt信号传导途径中的转录共激活因子，其中它结合Tcf/Lef家族转录因子。在缺乏Wnt信号的情况下，非连接β-连环蛋白存在于含有蛋白axin和腺瘤性结肠息肉病（APC）的多蛋白复合物中，两者都直接结合β-连环蛋白。已通过等温滴定量热法测定了β-连环蛋白与E-钙粘蛋白、Lef-1、APC、轴蛋白和转录抑制剂ICAT结合的热力学。大多数的相互作用表现出大的，不利的熵变，与这些配体在β-连环蛋白的情况下天然非结构化一致。钙粘蛋白和APC共同序列基序中丝氨酸残基的磷酸化使β-连环蛋白的亲和力增加了300-700倍，表面等离子体共振测量显示E-钙粘蛋白的磷酸化既增强了其结合速率又降低了其解离速率。使用缺少一个或两个尾的构建体也研究了位于β-连环蛋白犰狳重复结构域侧翼的N-和C-末端“尾”对配体结合的影响。与早期采用较少直接结合试验的研究相反，尾部不影响β-连环蛋白对紧密配体（如E-钙粘蛋白、Lef-1和磷酸化APC）的亲和力。然而，发现β-连环蛋白C-末端尾部降低了对较弱配体APC和轴蛋白的亲和力，表明该区域可能在β-连环蛋白降解中具有调节作用。
beta-Catenin is a structural component of adherens junctions, where it binds to the cytoplasmic domain of cadherin cell adhesion molecules. beta-Catenin is also a transcriptional coactivator in the Wnt signaling pathway, where it binds to Tcf/Lef family transcription factors. In the absence of a Wnt signal, nonjunctional beta-catenin is present in a multiprotein complex containing the proteins axin and adenomatous polyposis coli (APC), both of which bind directly to beta-catenin. The thermodynamics of beta-catenin binding to E-cadherin, Lef-1, APC, axin, and the transcriptional inhibitor ICAT have been determined by isothermal titration calorimetry. Most of the interactions showed large, unfavorable entropy changes, consistent with these ligands being natively unstructured in the absence of beta-catenin. Phosphorylation of serine residues present in a sequence motif common to cadherins and APC increased the affinity for beta-catenin 300-700-fold, and surface plasmon resonance measurements revealed that phosphorylation of E-cadherin both enhanced its on rate and decreased its off rate. The effects of the N- and C-terminal "tails" that flank the beta-catenin armadillo repeat domain on ligand binding have also been investigated using constructs lacking one or both tails. Contrary to earlier studies that employed less direct binding assays, the tails did not affect the affinity of beta-catenin for tight ligands such as E-cadherin, Lef-1, and phosphorylated APC. However, the beta-catenin C-terminal tail was found to decrease the affinity for the weaker ligands APC and axin, suggesting that this region may have a regulatory role in beta-catenin degradation.