Cytochrome P450-type Hydroxylation and Epoxidation in a Tyrosine-liganded Hemoprotein, Catalase-related Allene Oxide Synthase
Cytochrome P450-type Hydroxylation and Epoxidation in a Tyrosine-liganded Hemoprotein, Catalase-related Allene Oxide Synthase
复制标题
DOI：
10.1074/jbc.m112.364216
复制
发表时间：
2012-07-13
影响因子：
4.8
通讯作者：
Brash, Alan R.
中科院分区：
文献类型：
--
作者：
Boeglin, William E.;Brash, Alan R.
血红蛋白催化环氧化或羟基化反应的能力通常与半胱氨酸作为血红素的近端配体有关，如在细胞色素P450或一氧化氮合酶中。珊瑚丛中过氧化氢酶相关的氧化丙烯合成酶（cAOS）与过氧化氢酶本身一样，其近端血红素配体为酪氨酸。它的自然反应是将8r -氢过氧-二十碳四烯酸（8R-HPETE）转化为环氧烯，该反应由铁血红素激活，通过Fe-IV-OH中间体形成产物，化合物II。本文利用氧供体碘基苯将cAOS氧化为化合物I (Fe-V=O)，并考察了该酶的催化能力。8r -羟基二碳四烯酸（8R-HETE）是天然底物的羟基类似物，通常与cAOS不反应，因此在9,10双键上立体特异性环氧化，形成8r -羟基- 9r， 10r -反式环氧-二十碳- 5z，11Z， 14z -三烯酸作为主要产物；使用100 μ M碘基苯时，周转率为1/s。对映体，8S-HETE，立体特异性环氧化，虽然区域特异性较低，并在13和16个碳上羟基化。花生四烯酸转化为两种主要产物，8R- hete和8R， 9s -二十碳三烯酸（8R,9S-EET），以及其他手性单环氧化合物和双烯丙基10S-HETE。亚油酸被环氧化，而硬脂酸未被代谢。我们得出结论，当cAOS带氧供体时，它可以作为一个立体特异性的单加氧酶。我们的研究结果表明，在酪氨酸配体cAOS（一种与过氧化氢酶相关的血液蛋白，其中多不饱和脂肪酸可以进入活性位点）中，该酶具有模仿典型P450环氧合酶的活性和P450羟化酶的一些能力的潜力。
The ability of hemoproteins to catalyze epoxidation or hydroxylation reactions is usually associated with a cysteine as the proximal ligand to the heme, as in cytochrome P450 or nitric oxide synthase. Catalase-related allene oxide synthase (cAOS) from the coral Plexaura homomalla, like catalase itself, has tyrosine as the proximal heme ligand. Its natural reaction is to convert 8R-hydroperoxy-eicosatetraenoic acid (8R-HPETE) to an allene epoxide, a reaction activated by the ferric heme, forming product via the Fe-IV-OH intermediate, Compound II. Here we oxidized cAOS to Compound I (Fe-V=O) using the oxygen donor iodosylbenzene and investigated the catalytic competence of the enzyme. 8R-hydroxyeicosatetraenoic acid (8R-HETE), the hydroxy analog of the natural substrate, normally unreactive with cAOS, was thereby epoxidized stereospecifically on the 9,10 double bond to form 8R-hydroxy-9R, 10R-trans-epoxy-eicosa-5Z,11Z,14Z-trienoic acid as the predominant product; the turnover was 1/s using 100 mu M iodosylbenzene. The enantiomer, 8S-HETE, was epoxidized stereospecifically, although with less regiospecificity, and was hydroxylated on the 13- and 16-carbons. Arachidonic acid was converted to two major products, 8R-HETE and 8R,9S-eicosatrienoic acid (8R,9S-EET), plus other chiral monoepoxides and bis-allylic 10S-HETE. Linoleic acid was epoxidized, whereas stearic acid was not metabolized. We conclude that when cAOS is charged with an oxygen donor, it can act as a stereospecific monooxygenase. Our results indicate that in the tyrosine-liganded cAOS, a catalase-related hemoprotein in which a polyunsaturated fatty acid can enter the active site, the enzyme has the potential to mimic the activities of typical P450 epoxygenases and some capabilities of P450 hydroxylases.