Grininger Martin, Staudt Heike, Johansson Patrik, Wachtveitl Josef, Oesterhelt Dieter
Department of Membrane Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany.
J Biol Chem. 2009 May 8;284(19):13068-76. doi: 10.1074/jbc.M808063200. Epub 2009 Feb 17.
Flavins are employed to transform physical input into biological output signals. In this function, flavins catalyze a variety of light-induced reactions and redox processes. However, nature also provides flavoproteins with the ability to uncouple the mediation of signals. Such proteins are the riboflavin-binding proteins (RfBPs) with their function to store riboflavin for fast delivery of FMN and FAD. Here we present in vitro and in vivo data showing that the recently discovered archaeal dodecin is an RfBP, and we reveal that riboflavin storage is not restricted to eukaryotes. However, the function of the prokaryotic RfBP dodecin seems to be adapted to the requirement of a monocellular organism. While in eukaryotes RfBPs are involved in trafficking riboflavin, and dodecin is responsible for the flavin homeostasis of the cell. Although only 68 amino acids in length, dodecin is of high functional versatility in neutralizing riboflavin to protect the cellular environment from uncontrolled flavin reactivity. Besides the predominant ultrafast quenching of excited states, dodecin prevents light-induced riboflavin reactivity by the selective degradation of riboflavin to lumichrome. Coordinated with the high affinity for lumichrome, the directed degradation reaction is neutral to the cellular environment and provides an alternative pathway for suppressing uncontrolled riboflavin reactivity. Intriguingly, the different structural and functional properties of a homologous bacterial dodecin suggest that dodecin has different roles in different kingdoms of life.
黄素被用于将物理输入转化为生物输出信号。在这一功能中，黄素催化各种光诱导反应和氧化还原过程。然而，自然界也赋予了黄素蛋白解耦信号介导的能力。这类蛋白质就是核黄素结合蛋白（RfBPs），其功能是储存核黄素以便快速递送FMN和FAD。在此，我们展示了体外和体内数据，表明最近发现的古菌十二聚体蛋白是一种RfBP，并且我们揭示核黄素储存并不局限于真核生物。然而，原核生物的RfBP十二聚体蛋白的功能似乎是适应单细胞生物的需求。在真核生物中，RfBPs参与核黄素的运输，而十二聚体蛋白负责细胞的黄素稳态。尽管十二聚体蛋白仅有68个氨基酸长，但它在中和核黄素以保护细胞环境免受不受控制的黄素反应性影响方面具有高度的功能多样性。除了对激发态的主要超快猝灭作用外，十二聚体蛋白通过将核黄素选择性降解为光色素来防止光诱导的核黄素反应性。与对光色素的高亲和力相协调，定向降解反应对细胞环境是中性的，并提供了一条抑制不受控制的核黄素反应性的替代途径。有趣的是，同源细菌十二聚体蛋白的不同结构和功能特性表明，十二聚体蛋白在不同的生命王国中具有不同的作用。
