Department of Biochemistry, McGill University, Montreal, QC H3G 0B1, Canada.
Structure. 2013 Apr 2;21(4):517-27. doi: 10.1016/j.str.2013.01.015. Epub 2013 Mar 7.
Death-associated protein 5 (DAP5/p97) is a homolog of the eukaryotic initiation factor 4G (eIF4G) that promotes the IRES-driven translation of multiple cellular mRNAs. Central to its function is the middle domain (MIF4G), which recruits the RNA helicase eIF4A. The middle domain of eIF4G consists of tandem HEAT repeats that coalesce to form a solenoid-type structure. Here, we report the crystal structure of the DAP5 MIF4G domain. Its overall fold is very similar to that of eIF4G; however, significant conformational variations impart distinct surface properties that could explain the observed differences in IRES binding between the two proteins. Interestingly, quantitative analysis of the DAP5-eIF4A interaction using isothermal titration calorimetry reveals a 10-fold lower affinity than with the eIF4G-eIF4A interaction that appears to affect their ability to stimulate eIF4A RNA unwinding activity in vitro. This difference in stability of the complex may have functional implications in selecting the mode of translation initiation.
死亡相关蛋白 5（DAP5/p97）是真核起始因子 4G（eIF4G）的同源物，可促进多个细胞 mRNA 的 IRES 驱动翻译。其功能的核心是中间结构域（MIF4G），它可募集 RNA 解旋酶 eIF4A。eIF4G 的中间结构域由串联的 HEAT 重复组成，凝聚形成螺线管型结构。在这里，我们报告了 DAP5 MIF4G 结构域的晶体结构。它的整体折叠非常类似于 eIF4G；然而，显著的构象变化赋予了不同的表面特性，这可以解释两种蛋白质在 IRES 结合方面的观察到的差异。有趣的是，使用等温滴定量热法对 DAP5-eIF4A 相互作用进行定量分析表明，与 eIF4G-eIF4A 相互作用相比，亲和力低 10 倍，这似乎影响了它们在体外刺激 eIF4A RNA 解旋活性的能力。该复合物稳定性的差异可能在选择翻译起始模式方面具有功能意义。
