York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO1 5YW, UK.
J Struct Biol. 2010 Apr;170(1):127-33. doi: 10.1016/j.jsb.2010.01.013. Epub 2010 Feb 4.
Anti-TRAP (AT) protein regulates expression of tryptophan biosynthetic genes by binding to the trp RNA-binding attenuation protein (TRAP) and preventing its interaction with RNA. Bacillus subtilis AT forms trimers that can either interact with TRAP or can further assemble into dodecameric particles. To determine which oligomeric forms are preserved in AT proteins of other Bacilli we studied Bacillus licheniformis AT which shares 66% sequence identity with the B. subtilis protein. We show that in solution B. licheniformis AT forms stable trimers. In crystals, depending on pH, such trimers assemble into two different types of dodecameric particles, both having 23 point group symmetry. The dodecamer formed at pH 6.0 has the same conformation as previously observed for B. subtilis AT. This dodecamer contains a large internal chamber with the volume of approximately 700 A(3), which is lined by the side chains of twelve valine residues. The presence of the hydrophobic chamber hints at the possibility that the dodecamer formation could be induced by binding of a ligand. Interestingly, in the dodecamer formed at pH 8.0 all trimers are turned inside out relatively to the form observed at pH 6.0.
抗 TRAP（AT）蛋白通过与色氨酸 RNA 结合衰减蛋白（TRAP）结合并阻止其与 RNA 相互作用来调节色氨酸生物合成基因的表达。枯草芽孢杆菌 AT 形成三聚体，既可以与 TRAP 相互作用，也可以进一步组装成十二聚体颗粒。为了确定其他芽孢杆菌中的 AT 蛋白保留了哪种寡聚形式，我们研究了与枯草芽孢杆菌蛋白具有 66%序列同一性的地衣芽孢杆菌 AT。我们表明，在溶液中，地衣芽孢杆菌 AT 形成稳定的三聚体。在晶体中，根据 pH 值的不同，这些三聚体组装成两种不同类型的十二聚体颗粒，两者都具有 23 点群对称性。在 pH 值为 6.0 时形成的十二聚体具有与先前观察到的枯草芽孢杆菌 AT 相同的构象。该十二聚体包含一个大的内部腔室，体积约为 700 A（3），由十二个缬氨酸残基的侧链构成。疏水腔室的存在暗示了十二聚体形成可能是由配体结合诱导的。有趣的是，在 pH 值为 8.0 时形成的十二聚体中，所有三聚体相对于在 pH 值为 6.0 时观察到的形式都被翻转到内部。
