Higgins Luke J, Yan Feng, Liu Pinghua, Liu Hung-wen, Drennan Catherine L
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Nature. 2005 Oct 6;437(7060):838-44. doi: 10.1038/nature03924. Epub 2005 Jul 13.
The biosynthetic pathway of the clinically important antibiotic fosfomycin uses enzymes that catalyse reactions without precedent in biology. Among these is hydroxypropylphosphonic acid epoxidase, which represents a new subfamily of non-haem mononuclear iron enzymes. Here we present six X-ray structures of this enzyme: the apoenzyme at 2.0 A resolution; a native Fe(II)-bound form at 2.4 A resolution; a tris(hydroxymethyl)aminomethane-Co(II)-enzyme complex structure at 1.8 A resolution; a substrate-Co(II)-enzyme complex structure at 2.5 A resolution; and two substrate-Fe(II)-enzyme complexes at 2.1 and 2.3 A resolution. These structural data lead us to suggest how this enzyme is able to recognize and respond to its substrate with a conformational change that protects the radical-based intermediates formed during catalysis. Comparisons with other family members suggest why substrate binding is able to prime iron for dioxygen binding in the absence of alpha-ketoglutarate (a co-substrate required by many mononuclear iron enzymes), and how the unique epoxidation reaction of hydroxypropylphosphonic acid epoxidase may occur.
临床上重要的抗生素磷霉素的生物合成途径所使用的酶能催化生物学中前所未有的反应。其中包括羟丙基膦酸环氧化酶，它代表了非血红素单核铁酶的一个新亚家族。在此，我们展示了该酶的六种X射线结构：分辨率为2.0 Å的无辅基酶；分辨率为2.4 Å的天然Fe(II)结合形式；分辨率为1.8 Å的三（羟甲基）氨基甲烷-Co(II)-酶复合物结构；分辨率为2.5 Å的底物-Co(II)-酶复合物结构；以及分辨率分别为2.1 Å和2.3 Å的两种底物-Fe(II)-酶复合物。这些结构数据使我们能够提出该酶如何通过构象变化识别并响应其底物，这种构象变化能保护催化过程中形成的基于自由基的中间体。与其他家族成员的比较表明了为什么在没有α-酮戊二酸（许多单核铁酶所需的共底物）的情况下底物结合能够使铁为双氧结合做好准备，以及羟丙基膦酸环氧化酶独特的环氧化反应可能是如何发生的。
