Lawson C L, Zhang R G, Schevitz R W, Otwinowski Z, Joachimiak A, Sigler P B
Department of Biochemistry and Molecular Biology, University of Chicago, Illinois 60637.
Proteins. 1988;3(1):18-31. doi: 10.1002/prot.340030103.
An orthorhombic crystal form of trp repressor (aporepressor plus L-tryptophan ligand) was solved by molecular replacement, refined to 1.65 A resolution, and compared to the structure of the repressor in trigonal crystals. Even though these two crystal forms of repressor were grown under identical conditions, the refined structures have distinctly different conformations of the DNA-binding domains. Unlike the repressor/aporepressor structural transition, the conformational shift is not caused by the binding or loss of the L-tryptophan ligand. We conclude that while L-tryptophan binding is essential for forming a specific complex with trp operator DNA, the corepressor ligand does not lock the repressor into a single conformation that is complementary to the operator. This flexibility may be required by the various binding modes proposed for trp repressor in its search for and adherence to its three different operator sites.
通过分子置换解析了色氨酸阻遏物（无辅阻遏物加L-色氨酸配体）的正交晶型，精修至1.65埃分辨率，并与三角晶体中阻遏物的结构进行了比较。尽管这两种阻遏物晶体形式是在相同条件下生长的，但精修后的结构在DNA结合结构域的构象上有明显差异。与阻遏物/无辅阻遏物的结构转变不同，这种构象变化不是由L-色氨酸配体的结合或丢失引起的。我们得出结论，虽然L-色氨酸结合对于与色氨酸操纵子DNA形成特异性复合物至关重要，但辅阻遏物配体不会将阻遏物锁定在与操纵子互补的单一构象中。色氨酸阻遏物在寻找和附着其三个不同的操纵子位点时提出的各种结合模式可能需要这种灵活性。
