BirA催化生物素的腺苷酸化和随后共价连接到生物素羧基载体蛋白(BCCP)。在没有apo-BCCP的情况下,生物素-5'-AMP充当诱导BirA二聚化并与生物操纵子结合以抑制生物素生物合成的共阻遏物。apo-BirA的晶体结构,和BirA与生物素的复合物已经被报道。我们在这里描述了BirA与共阻遏物类似物biotinol-5'-AMP复合的2.8A分辨率晶体结构。先前表明,apo-BirA的结构是单体的,并且生物素的结合弱诱导了二聚体结构,其中三个无序的表面环被组织起来以形成二聚体界面。共阻遏复合物的结构也是二聚体,显然与BirA有关。生物素结构,但有几个显著的构象变化。迄今为止无序的“腺苷酸结合环”形成了覆盖共阻遏物的明确定义的结构。共阻遏物支撑二聚体界面,导致改善的包装和铰链弯曲角度沿二聚体界面相对于BirA的12度变化。生物素结构。这有助于解释为什么协同阻遏物的结合对于优化BirA与bioO操纵子的结合是必要的。该结构揭示了核苷酸结合基序GXGXXG在结合腺苷酸和控制阻遏物功能中的意外用途。最后,基于结构分析,我们提出由BirA代表的腺苷酸酶类别,脂蛋白连接酶和II类tRNA合成酶早期分化,并根据其隔离辅因子或氨基酸残基的能力进行选择,和腺苷酸化活性通过功能收敛独立产生。
BirA catalyzes the adenylation and subsequent covalent attachment of biotin to the biotin carboxyl carrier protein (BCCP). In the absence of apo-BCCP, biotin-5\'-AMP acts as a co-repressor that induces BirA dimerization and binding to the bio operator to repress biotin biosynthesis. The crystal structures of apo-BirA, and BirA in complex with biotin have been reported. We here describe the 2.8A resolution crystal structure of BirA in complex with the co-repressor analog biotinol-5\'-AMP. It was previously shown that the structure of apo-BirA is monomeric and that binding of biotin weakly induces a dimeric structure in which three disordered surface loops become organized to form the dimer interface. The structure of the co-repressor complex is also a dimer, clearly related to the BirA.biotin structure, but with several significant conformational changes. A hitherto disordered \"adenylate binding loop\" forms a well-defined structure covering the co-repressor. The co-repressor buttresses the dimer interface, resulting in improved packing and a 12 degrees change in the hinge-bending angle along the dimer interface relative to the BirA.biotin structure. This helps explain why the binding of the co-repressor is necessary to optimize the binding of BirA to the bioO operator. The structure reveals an unexpected use of the nucleotide-binding motif GXGXXG in binding adenylate and controlling the repressor function. Finally, based on structural analysis we propose that the class of adenylating enzymes represented by BirA, lipoate protein ligase and class II tRNA synthetases diverged early and were selected based on their ability to sequester co-factors or amino acid residues, and adenylation activity arose independently through functional convergence.