Park Kiyoung, Mera Paola E, Moore Theodore C, Escalante-Semerena Jorge C, Brunold Thomas C
Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706 (USA).
Present address: Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon (Republic of Korea).
Angew Chem Int Ed Engl. 2015 Jun 8;54(24):7158-61. doi: 10.1002/anie.201501930. Epub 2015 Apr 27.
Three distinct families of ATP:corrinoid adenosyltransferases (ACATs) exist that are capable of converting vitamin B12 derivatives into coenzyme B12 by catalyzing the thermodynamically challenging reduction of Co(II) rrinoids to form "supernucleophilic" Co(I) intermediates. While the structures and mechanisms of two of the ACAT families have been studied extensively, little is known about the EutT enzymes beyond the fact that they exhibit a unique requirement for a divalent metal cofactor for enzymatic activity. In this study we have obtained compelling evidence that EutT converts cob(II)alamin into an effectively four-coordinate Co(II) species so as to facilitate Co(II)→Co(I) reduction. Intriguingly, EutT fails to promote axial ligand dissociation from the substrate analogue cob(II)inamide, a natural precursor of cob(II)alamin. This unique substrate specificity of EutT has important physiological implications.
存在三种不同的ATP：类咕啉腺苷转移酶（ACAT）家族，它们能够通过催化热力学上具有挑战性的Co（II）类咕啉还原反应，将维生素B12衍生物转化为辅酶B12，形成“超亲核”Co（I）中间体。虽然对其中两个ACAT家族的结构和机制已经进行了广泛研究，但除了它们对二价金属辅因子具有独特的酶活性要求这一事实外，对EutT酶的了解甚少。在本研究中，我们获得了令人信服的证据，即EutT将钴胺素（II）转化为一种有效的四配位Co（II）物种，以促进Co（II）→Co（I）的还原。有趣的是，EutT不能促进底物类似物钴胺酰胺（II）（钴胺素（II）的天然前体）的轴向配体解离。EutT这种独特的底物特异性具有重要的生理意义。
