Cofactor dependence of reduction potentials for [4Fe-4S]2+/1+ in lysine 2,3-aminomutase
Cofactor dependence of reduction potentials for [4Fe-4S]2+/1+ in lysine 2,3-aminomutase
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DOI：
10.1021/bi0519497
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发表时间：
2006-03-14
期刊：
影响因子：
2.9
通讯作者：
Frey, PA
中科院分区：
文献类型：
--
作者：
Hinckley, GT;Frey, PA
赖氨酸2,3-氨基交换酶（LAM）通过自由基机制催化l -赖氨酸和l -赖氨酸的相互转化。s -腺苷- l-蛋氨酸（SAM）的还原裂解产生的5'-脱氧腺苷自由基引发底物自由基的形成。LAM中的[4Fe-4S]（1+）簇是SAM还原解理中的单电子源，它直接连接到簇中独特的铁位点。本文报道了在SAM、s -腺苷- l-同型半胱氨酸（SAH）或5′-{N-[(3S)-3-氨基羧基丙基]-N-甲基氨基-5′-脱氧腺苷（azaSAM）存在下[4Fe-4S]（2+/1+）偶对的中点还原电位。在SAM存在时，还原电位为-430 +/- 2 mV；在SAH存在时，还原电位为-460 +/- 3 mV；在azaSAM存在时，还原电位为-497 +/- 10 mV。在没有SAM或类似物的情况下，存在二硫苏糖醇、二氢脂酸盐或半胱氨酸作为独特铁的配体，中点电位分别为-479 +/- 5、-516 +/- 5和-484 +/- 3 mV。LAM是自由基SAM超家族的一员，其中CxxxCxxC基序为[4Fe-4S]簇中的铁提供了三个硫酸盐配体，SAM将蛋氨酸基部分的α -氨基和α -羧酸基作为第四个铁的配体。结果表明，类铁氧化还原蛋白[4Fe-4S]簇的还原电位在中等范围内。他们表明，相对于二氢脂酸盐作为簇配体，SAM将还原电位提高了86 mV。这一差异解释了先前报道的二硫代石对sam依赖的[4Fe-4S]（2+）簇的还原。地对空导弹的类似物提高电位的能力较弱。我们得出结论，与SAM连接的簇的中点还原电位比水溶液中简单烷基磺酸离子的单电子还原裂解的半波电位负1.2 V。利用结合能可以克服SAM还原裂解过程中的能垒。
Lysine 2,3-aminomutase (LAM) catalyzes the interconversion Of L-lysine and L-beta-lysine by a free radical mechanism. The 5'-deoxyadenosyl radical derived from the reductive cleavage of S-adenosyl-L-methionine (SAM) initiates substrate-radical formation. The [4Fe-4S](1+) cluster in LAM is the one-electron source in the reductive cleavage of SAM, which is directly ligated to the unique iron site in the cluster. We here report the midpoint reduction potentials of the [4Fe-4S](2+/1+) couple in the presence of SAM, S-adenosyl-L-homocysteine (SAH), or 5'-{N-[(3S)-3-aminocarboxypropyl]-N-methylaminol-5'-deoxyadenosine (azaSAM) as measured by spectroelectrochemistry. The reduction potentials are -430 +/- 2 mV in the presence of SAM, -460 +/- 3 mV in the presence of SAH, and -497 +/- 10 mV in the presence of azaSAM. In the absence of SAM or an analogue and the presence of dithiothreitol, dihydrolipoate, or cysteine as ligands to the unique iron, the midpoint potentials are -479 +/- 5, -516 +/- 5, and -484 +/- 3 mV, respectively. LAM is a member of the radical SAM superfamily of enzymes, in which the CxxxCxxC motif donates three thiolate ligands to iron in the [4Fe-4S] cluster and SAM donates the alpha-amino and alpha-carboxylate groups of the methionyl moiety as ligands to the fourth iron. The results show the reduction potentials in the midrange for ferredoxin-like [4Fe-4S] clusters. They show that SAM elevates the reduction potential by 86 mV relative to that of dihydrolipoate as the cluster ligand. This difference accounts for the SAM-dependent reduction of the [4Fe-4S](2+) cluster by dithionite reported earlier. Analogues of SAM have a weakened capacity to raise the potential. We conclude that the midpoint reduction potential of the cluster ligated to SAM is 1.2 V less negative than the half-wave potential for the one-electron reductive cleavage of simple alkylsulfonium ions in aqueous solution. The energetic barrier in the reductive cleavage of SAM may be overcome through the use of binding energy.