Esser D, Bauer B, Wolthuis R M, Wittinghofer A, Cool R H, Bayer P
Max-Planck-Institut für molekulare Physiologie, Abteilung Strukturelle Biologie, Abteilung Physikalische Biochemie, Dortmund, Germany.
Biochemistry. 1998 Sep 29;37(39):13453-62. doi: 10.1021/bi9811664.
Ral-specific guanine nucleotide exchange factors RalGDS, Rgl, and Rlf have been suggested to function as intermediates between Ras and Ral pathways by being able to bind Ras proteins through their C-terminal Ras-binding domains (RBD). The RBDs of RalGDS and of the Ser/Thr kinase c-Raf-1 have been shown to have the same tertiary structure. In contrast to the RBDs of Raf and RalGDS, which bind either Ras or Rap with high affinity, Rlf-RBD has a similar affinity for both GTP-binding proteins. To be able to compare these RBDs on a structural level, we have solved the three-dimensional structure of Rlf-RBD by NMR spectroscopy. The overall tertiary structure of Rlf-RBD shows the betabetaalphabetabetaalphabeta-fold of the ubiquitin superfamily and is very similar to that of RalGDS-RBD. The binding interface of Rlf-RBD to Ras was mapped using chemical shift analysis and indicated a binding mode similar to that in the case of Rap.Raf-RBD. However, comparison of the putatively interacting regions revealed structural differences which are proposed to be responsible for the different substrate affinities of Rlf-, RalGDS-, and Raf-RBD.
已有人提出，Ral特异性鸟嘌呤核苷酸交换因子RalGDS、Rgl和Rlf可作为Ras和Ral信号通路之间的中间体，因为它们能够通过其C端Ras结合结构域（RBD）与Ras蛋白结合。RalGDS和丝氨酸/苏氨酸激酶c-Raf-1的RBD已被证明具有相同的三级结构。与Raf和RalGDS的RBD不同，后者能高亲和力地结合Ras或Rap，而Rlf-RBD对这两种GTP结合蛋白具有相似的亲和力。为了能够在结构水平上比较这些RBD，我们通过核磁共振光谱法解析了Rlf-RBD的三维结构。Rlf-RBD的整体三级结构显示出泛素超家族的βββαββα折叠，与RalGDS-RBD非常相似。利用化学位移分析绘制了Rlf-RBD与Ras的结合界面，结果表明其结合模式与Rap·Raf-RBD的情况相似。然而，对假定相互作用区域的比较揭示了结构差异，这些差异被认为是导致Rlf-、RalGDS-和Raf-RBD对不同底物亲和力不同的原因。
