The dodecin from Thermus thermophilus, a bifunctional cofactor storage protein
The dodecin from Thermus thermophilus, a bifunctional cofactor storage protein
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DOI：
10.1074/jbc.m704951200
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发表时间：
2007-11-09
影响因子：
4.8
通讯作者：
Essen, Lars-Oliver
中科院分区：
文献类型：
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作者：
Meissner, Britta;Schleicher, Erik;Essen, Lars-Oliver
十二肽是到目前为止已知的最小的黄素蛋白(68-71个氨基酸)，很可能参与原核生物黄素的储存。十二肽单体采用简单的β-α-β-折叠，并组装成中空球状十二聚体络合物。用等温滴定、量热法和荧光滴定等方法研究了嗜热菌十二肽与黄素结合的化学计量比和表观离解常数在亚微摩尔到纳摩尔范围的变化。嗜热梭菌十二烷基硫蛋白的黄素预结合状态和FMN重组状态的X射线结构揭示了FMN二聚体在一种新的Si-si中的结合，而不是像以前在古菌十二烷基蛋白中发现的那样其异四氮嗪部分的重定向。电子顺磁共振研究表明，还原时多余的电子只局限在一个黄素上，从而使十二烷基黄素结合的黄素对氧化还原化学非常不稳定。除了FMN二聚体外，辅酶A的三聚体还沿着十二烷基硫酸酯复合体的三重对称面II与该真细菌十二烷基硫酸酯结合。因此，十二肽可以作为双功能辅因子存储蛋白，以聚集和非反应状态非常有效地隔离原核生物中的催化辅因子。
Dodecins are so far the smallest known flavoproteins ( 68 - 71 amino acids) and are most likely involved in prokaryotic flavin storage. The dodecin monomers adopt a simple beta alpha beta beta-fold and assemble to hollow sphere-like dodecameric complexes. Flavin binding by the dodecin from Thermus thermophilus showed a 1: 1 stoichiometry and apparent dissociation constants in the submicromolar to nanomolar range as characterized by isothermal titration calorimetry and fluorescence titrations. The x-ray structures of the flavin-prebound and FMN-reconstituted state of the T. thermophilus dodecin revealed binding of FMN dimers in a novel si-si-rather than the re-re-orientation of their isoalloxazine moieties as found before in an archaeal dodecin. Electron paramagnetic resonance studies demonstrated that upon reduction the excess electron is localized only on one flavin, thus making dodecin-bound flavins highly refractory to redox chemistry. Besides FMN dimers, trimers of coenzyme A are additionally bound to this eubacterial dodecin along the 3-fold symmetry face II of the dodecin complex. Therefore, dodecins can act as bifunctional cofactor storage proteins that sequester catalytic cofactors in prokaryotes very efficiently in an aggregated and unreactive state.