O'Neil K T, Shuman J D, Ampe C, DeGrado W F
Central Research and Development Department, DuPont Company, Wilmington, Delaware 19880-0328.
Biochemistry. 1991 Sep 17;30(37):9030-4. doi: 10.1021/bi00101a017.
Leucine zipper proteins comprise a recently identified class of DNA binding proteins that contain a bipartite structural motif consisting of a "leucine zipper" dimerization domain and a segment rich in basic residues responsible for DNA interaction. Protein fragments encompassing the zipper plus basic region domains (bZip) have previously been used to determine the conformational and dynamic properties of this motif. In the absence of DNA, the coiled-coil portion is alpha-helical and dimeric, whereas the basic region is flexible and partially disordered. Addition of DNA containing a specific recognition sequence induces a fully helical conformation in the basic regions of these fragments. However, the question remained whether the same conformational change would be observed in native bZip proteins where the basic regions might be stabilized in an alpha-helical conformation even in the absence of DNA, through interactions with portions of the protein not included in the bZip motif. We have now examined the DNA-induced conformational transition for an intact bZip protein, GCN4, and for the bZip fragment of C/EBP with two enhancers that are differentially symmetric. Our results are consistent with the induced helical fork model wherein the basic regions are largely flexible in the absence of DNA and become fully helical in the presence of the specific DNA recognition sequence.
亮氨酸拉链蛋白是最近发现的一类DNA结合蛋白，其包含由“亮氨酸拉链”二聚化结构域和富含负责DNA相互作用的碱性残基的片段组成的双结构基序。先前已使用包含拉链加碱性区域结构域（bZip）的蛋白质片段来确定该基序的构象和动力学性质。在没有DNA的情况下，卷曲螺旋部分是α-螺旋且为二聚体，而碱性区域是灵活的且部分无序。添加含有特定识别序列的DNA会在这些片段的碱性区域诱导出完全螺旋构象。然而，问题仍然存在：在天然bZip蛋白中是否会观察到相同的构象变化，在天然bZip蛋白中，即使在没有DNA的情况下，碱性区域也可能通过与bZip基序中未包含的蛋白质部分相互作用而稳定在α-螺旋构象中。我们现在已经研究了完整的bZip蛋白GCN4以及具有两个差异对称增强子的C/EBP的bZip片段的DNA诱导的构象转变。我们的结果与诱导螺旋叉模型一致，在该模型中，碱性区域在没有DNA的情况下基本是灵活的，而在存在特定DNA识别序列的情况下会变成完全螺旋的。
