Coordination and mechanism of reversible cleavage of S-adenosylmethionine by the [4Fe-4S] center in lysine 2,3-aminomutase
Coordination and mechanism of reversible cleavage of S-adenosylmethionine by the [4Fe-4S] center in lysine 2,3-aminomutase
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DOI：
10.1021/ja036120z
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发表时间：
2003-10-01
影响因子：
15
通讯作者：
Frey, PA
中科院分区：
文献类型：
--
作者：
Chen, DW;Walsby, C;Frey, PA
赖氨酸2，3-氨基变位酶(LAM)催化l-赖氨酸和l-β-赖氨酸的相互转化，其作用机制是C5‘−-S键可逆、还原均裂，生成蛋氨酸和活性中心的5’-脱氧腺苷自由基。LAM是酶超家族中的一个成员，在这个超家族中，[4Fe-4S]+簇与一个独特的非半胱氨酸铁配位，提供SAM裂解所需的电子。人们对电子插入SAM的机制知之甚少，也不知道该家族的所有酶是否都采用相同的机制。Se-腺苷-L-硒蛋氨酸(SESAM)取代SAM反应中的Se-X-射线吸收光谱(XAS)表明，电子转移是通过一个内球机制进行的，最终导致SeSAM裂解时硒蛋氨酸与铁的直接连接。在这里，我们报告了LAM的电子核双共振(Endor)光谱研究，它已经被14N，17O，2H，或13C标记的SAM所结合。研究发现，LAM与[4Fe-4S]+，2+簇结合的基序与丙酮酸甲酸裂解酶相同： 被SAM的氨基和羧基的独特铁所络合；蛋氨酸甲基靠近簇。然而，在SAM结合几何的细节上似乎有显著的差异，并且可能在机械上是重要的。根据Endor和XAS光谱结果的关联，我们推测了LAM裂解SAM生成中间体的机制，其中蛋氨酸产物的N、O和S结合到[4Fe-4S]团簇的八面体唯一Fe上。
Lysine 2,3-aminomutase (LAM) catalyzes the interconversion ofl-lysine andl-β-lysine, by a radical mechanism initiated by the reversible, reductive homolytic scission of the C5‘−S bond inS-adenosylmethionine (SAM) to form methionine and the 5‘-deoxyadenosyl radical at the active site. LAM is a member of a superfamily of enzymes in which a [4Fe-4S]+cluster with a unique, noncysteinyl coordinated Fe provides the electron required in the cleavage of SAM. Little is known of the mechanism by which the electron is inserted into SAM, and it is not known whether all enzymes of the family employ the same mechanism. Selenium X-ray absorption spectroscopy (XAS) in the reaction ofSe-adenosyl-l-selenomethionine (SeSAM) in place of SAM shows that electron transfer occurs by an inner sphere mechanism culminating in direct ligation of selenomethionine to iron upon cleavage ofSeSAM. Here, we report an electron nuclear double resonance (ENDOR) spectroscopic investigation of LAM to which has been bound14N,17O,2H, or13C labeled SAM. It is found that LAM exhibits the same motif for SAM binding to the [4Fe-4S]+,2+clusters as does pyruvate formate lyase: chelation by the unique iron of the amino and carboxylato groups of SAM; close proximity of the methionine methyl group to the cluster. However, there appear to be significant, and possibly mechanistically important, differences in the details of the binding geometry of SAM. On the basis of the correlation of the ENDOR and XAS spectroscopic results, we postulate a mechanism by which LAM cleaves SAM to generate an intermediate where N, O, and S of the methionine product are bound to the octahedrally coordinated unique Fe of the [4Fe-4S] cluster.