Pérez I, McAfee J G, Patton J G
Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee 37235, USA.
Biochemistry. 1997 Sep 30;36(39):11881-90. doi: 10.1021/bi9711745.
Polypyrimidine tract binding protein (PTB) is a 57 kD hnRNP protein (hnRNP I) that binds to the pyrimidine tract typically found near the 3' end of introns. Primary sequence analysis suggests that PTB contains four RNA recognition motifs (RRMs). Data from comparative structural and deletional analysis of PTB are consistent with the presence of a four reiterated domain structure. Since PTB exists in solution as a homodimer, it contains an oligomeric array of eight RRMs. Though the function of RRMs in a monomeric context has been addressed, the significance of their presence in an oligomeric context has not been investigated. To correlate structural motifs with function, we have analyzed the RNA binding properties of wild-type and deletion constructs of PTB that contain RRMs in both an oligomeric and monomeric context. These studies indicate that there is not a strong correlation between the RNA binding affinity and specificity upon oligomerization. However, the mode of RNA interaction and dimerization is linked. We have also found that the primary contributor to the free energy of PTB binding and the primary determinant for RNA binding specificity resides in RRM 3, while the primary contributor to dimer stabilization coincides with residues in RRM 2.
聚嘧啶序列结合蛋白（PTB）是一种57 kD的不均一核糖核蛋白（hnRNP）（hnRNP I），它能与通常位于内含子3'端附近的嘧啶序列结合。一级序列分析表明，PTB含有四个RNA识别基序（RRMs）。对PTB进行比较结构和缺失分析的数据与存在四个重复结构域结构一致。由于PTB在溶液中以同源二聚体形式存在，它包含一个由八个RRMs组成的寡聚阵列。尽管已经研究了单体情况下RRMs的功能，但尚未研究它们在寡聚情况下存在的意义。为了将结构基序与功能联系起来，我们分析了野生型和缺失构建体PTB在寡聚和单体情况下的RNA结合特性。这些研究表明，寡聚化后RNA结合亲和力和特异性之间没有很强的相关性。然而，RNA相互作用和二聚化的模式是相关的。我们还发现，PTB结合自由能的主要贡献者和RNA结合特异性的主要决定因素存在于RRM 3中，而二聚体稳定的主要贡献者与RRM 2中的残基一致。
