Layer Gunhild, Kervio Eric, Morlock Gaby, Heinz Dirk W, Jahn Dieter, Retey Janos, Schubert Wolf-Dieter
Institute of Microbiology, Technical University of Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany.
Biol Chem. 2005 Oct;386(10):971-80. doi: 10.1515/BC.2005.113.
Radical SAM enzymes have only recently been recognized as an ancient family sharing an unusual radical-based reaction mechanism. This late appreciation is due to the extreme oxygen sensitivity of most radical SAM enzymes, making their characterization particularly arduous. Nevertheless, realization that the novel apposition of the established cofactors S-adenosylmethionine and [4Fe-4S] cluster creates an explosive source of catalytic radicals, the appreciation of the sheer size of this previously neglected family, and the rapid succession of three successfully solved crystal structures within a year have ensured that this family has belatedly been noted. In this review, we report the characterization of two enzymes: the established radical SAM enzyme, HemN or oxygen-independent coproporphyrinogen III oxidase from Escherichia coli, and littorine mutase, a presumed radical SAM enzyme, responsible for the conversion of littorine to hyoscyamine in plants. The enzymes are compared to other radical SAM enzymes and in particular the three reported crystal structures from this family, HemN, biotin synthase and MoaA, are discussed.
自由基S-腺苷甲硫氨酸（SAM）酶直到最近才被确认为一个古老的家族，它们共享一种不同寻常的基于自由基的反应机制。这种认识较晚是因为大多数自由基SAM酶对氧极度敏感，这使得对它们的表征格外艰巨。尽管如此，由于认识到已确立的辅因子S-腺苷甲硫氨酸和[4Fe-4S]簇的新组合产生了催化自由基的爆发源，意识到这个先前被忽视的家族规模庞大，以及一年内相继成功解析出三个晶体结构，这个家族终于姗姗来迟地受到关注。在这篇综述中，我们报告了两种酶的表征：已确立的自由基SAM酶、来自大肠杆菌的HemN或不依赖氧的粪卟啉原III氧化酶，以及滨海藜芦碱变位酶，一种推测的自由基SAM酶，负责植物中滨海藜芦碱向莨菪碱的转化。将这些酶与其他自由基SAM酶进行了比较，特别是讨论了该家族已报道的三个晶体结构，即HemN、生物素合酶和MoaA。
