Molle Thibaut, Clémancey Martin, Latour Jean-Marc, Kathirvelu Velavan, Sicoli Giuseppe, Forouhar Farhad, Mulliez Etienne, Gambarelli Serge, Atta Mohamed
Laboratoire de Chimie et Biologie des Métaux, team "Biocatalyse", Biosciences and Biotechnology Institute of Grenoble (BIG), BIG-LCBM/Biocat, UMR 5249 CEA/CNRS/UGA, CEA/Grenoble, 17, rue des Martyrs, Grenoble, France.
Laboratoire de Chimie et Biologie des Métaux, team "Physicochimie des Métaux en Biologie" Biosciences and Biotechnology Institute of Grenoble (BIG), BIG-LCBM/PMB, UMR 5249 CEA/CNRS/UGA, CEA/Grenoble, 17, rue des Martyrs, Grenoble, France.
J Biol Inorg Chem. 2016 Jul;21(4):549-57. doi: 10.1007/s00775-016-1365-8. Epub 2016 Jun 3.
Radical SAM enzymes generally contain a 4Fe-4S (RS cluster) cluster bound to the protein via the three cysteines of a canonical motif CxxxCxxC. The non-cysteinyl iron is used to coordinate SAM via its amino-carboxylate moiety. The coordination-induced proximity between the cluster acting as an electron donor and the adenosyl-sulfonium bond of SAM allows for the homolytic cleavage of the latter leading to the formation of the reactive 5'-deoxyadenosyl radical used for substrate activation. Most of the structures of Radical SAM enzymes have been obtained in the presence of SAM, and therefore, little is known about the situation when SAM is not present. In this report, we show that RimO, a methylthiotransferase belonging to the radical SAM superfamily, binds a Tris molecule in the absence of SAM leading to specific spectroscopic signatures both in Mössbauer and pulsed EPR spectroscopies. These data provide a cautionary note for researchers who work with coordinative unsaturated iron sulfur clusters.
自由基S-腺苷甲硫氨酸（SAM）酶通常含有一个通过典型基序CxxxCxxC的三个半胱氨酸与蛋白质结合的4Fe-4S（RS簇）簇。非半胱氨酸铁用于通过其氨基羧酸盐部分配位SAM。作为电子供体的簇与SAM的腺苷锍键之间的配位诱导接近，使得后者能够进行均裂裂解，从而形成用于底物活化的活性5'-脱氧腺苷自由基。大多数自由基SAM酶的结构是在存在SAM的情况下获得的，因此，对于不存在SAM时的情况了解甚少。在本报告中，我们表明，属于自由基SAM超家族的甲基硫转移酶RimO在不存在SAM的情况下结合一个Tris分子，导致在穆斯堡尔光谱和脉冲电子顺磁共振光谱中出现特定的光谱特征。这些数据为研究配位不饱和铁硫簇的研究人员提供了一个警示。
