Mechanism of Radical Initiation in the Radical S-Adenosyl-l-methionine Superfamily.
Mechanism of Radical Initiation in the Radical S-Adenosyl-l-methionine Superfamily.
复制标题
DOI：
10.1021/acs.accounts.8b00356
复制
发表时间：
2018-11-20
影响因子：
18.3
通讯作者：
Broderick JB
中科院分区：
文献类型：
--
作者：
Broderick WE;Hoffman BM;Broderick JB
识别S-腺苷-L-蛋氨酸(SAM)酶这个庞大超家族的种子是在20世纪60年代播下的，当时Joachim Knappe发现丙酮酸的异化依赖于SAM和Fe(II)，Barker和他的同事对赖氨酸2，3-氨基变位酶也做了类似的观察。这些有趣的观察，再加上SAM和Fe是这些酶系统催化自由基的辅助因子的证据，促使我们在20世纪90年代探索Fe(II)和SAM是如何启动自由基反应的。我们早期的工作集中在Knappe最初表征的同一种酶：丙酮酸甲酸裂解酶激活酶(PFL-AE)。我们在这种酶中发现了一个铁-硫簇，加上当时其他SAM依赖酶的类似发现，导致了一类新兴的酶的认识，这种酶利用铁-硫簇来裂解SAM，释放出启动自由基反应的5‘-脱氧腺苷自由基(5’-DAO)。Heidi Sofia和他的同事进行的一项重要的生物信息学研究发现了被称为自由基SAM的酶超家族，现在已知它跨越了生命的所有王国，具有超过10万个独特的编码酶的序列，这些酶催化着非常多样化的反应。尽管序列相似性有限，催化的反应差异很大，但自由基SAM酶似乎采用了一种共同的机制来启动自由基化学，这一机制我们在过去25年里一直在帮助澄清。还原的[4Fe-4S]+团簇为SAM的还原裂解提供了所需的电子。生成的[4Fe-4S]~(2+)团簇既可以用SAM作辅助底物用外部还原剂还原，也可以用SAM作辅因子时SAM重整时提供的电子再还原。SAM的氨基和羧基与催化的[4Fe-4S]簇的独特的铁结合，使SAM的硫与簇非常接近。最近令人惊讶的结果表明，SAM的酶促裂解在5‘-DADO释放之前产生了一种有机金属中间体，从而启动了底物上的自由基化学。这种有机金属中间体，标记为Ω，具有一个5‘-脱氧腺苷部分，通过5’-C直接结合到[4Fe-4S]簇的唯一铁上，给出了一种直接类似于有机金属辅因子腺苷钴胺的Co-(5‘-C)键的结构。我们观察到这种中间Ω在整个超家族中都有形成，这表明它是启动自由基自组装反应的关键中间体，而且有机金属化学在生物学中的相关性比之前认为的要广泛得多。
The seeds for recognition of the vast superfamily of radical S-adenosyl-L-methionine (SAM) enzymes were sown in the 1960s, when Joachim Knappe found that the dissimilation of pyruvate was dependent on SAM and Fe(II), and Barker and co-workers made similar observations for lysine 2,3-aminomutase. These intriguing observations, coupled with the evidence that SAM and Fe were cofactors in radical catalysis by these enzyme systems, drew us in the 1990s to explore how Fe(II) and SAM initiate radical reactions. Our early work focused on the same enzyme Knappe had originally characterized: the pyruvate formate-lyase activating enzyme (PFL-AE). Our discovery of an iron-sulfur cluster in this enzyme, together with similar findings for other SAM-dependent enzymes at the time, led to the recognition of an emerging class of enzymes that use iron-sulfur clusters to cleave SAM, liberating the 5′-deoxyadenosyl radical (5′-dAdo●) that initiates radical reactions. A major bioinformatics study by Heidi Sofia and co-workers identified the enzyme superfamily denoted Radical SAM, now known to span all kingdoms of life with more than 100,000 unique sequences encoding enzymes that catalyze remarkably diverse reactions. Despite the limited sequence similarity and vastly divergent reactions catalyzed, the radical SAM enzymes appear to employ a common mechanism for initiation of radical chemistry, a mechanism we have helped to clarify over the last 25 years. A reduced [4Fe-4S]+ cluster provides the electron needed for the reductive cleavage of SAM. The resulting [4Fe-4S]2+ cluster can be rereduced either by an external reductant, with SAM acting as a cosubstrate, or by an electron provided during the reformation of SAM in cases where SAM is used as a cofactor. The amino and carboxylate groups of SAM bind to the unique iron of the catalytic [4Fe-4S] cluster, placing the sulfonium of SAM in close proximity to the cluster. Surprising recent results have shown that the initiating enzymatic cleavage of SAM generates an organometallic intermediate prior to liberation of 5′-dAdo●, which initiates radical chemistry on the substrate. This organometallic intermediate, denoted Ω, has a 5′-deoxyadenosyl moiety directly bound to the unique iron of the [4Fe-4S] cluster via the 5′-C, giving a structure that is directly analogous to the Co-(5′- C) bond of the organometallic cofactor adenosylcobalamin. Our observation that this intermediate Ω is formed throughout the superfamily suggests that this is a key intermediate in initiating radical SAM reactions, and that organometallic chemistry is much more broadly relevant in biology than previously thought.
登录
查看更多内容
影响因子：
16.6
作者：
Driesener, Rebecca C.;Challand, Martin R.;Roach, Peter L.
通讯作者：
Roach, Peter L.
影响因子：
15
作者：
Byer AS;Yang H;McDaniel EC;Kathiresan V;Impano S;Pagnier A;Watts H;Denler C;Vagstad AL;Piel J;Duschene KS;Shepard EM;Shields TP;Scott LG;Lilla EA;Yokoyama K;Broderick WE;Hoffman BM;Broderick JB
通讯作者：
Broderick JB
影响因子：
15
作者：
Henshaw, TF;Cheek, J;Broderick, JB
通讯作者：
Broderick, JB
DOI：
10.1006/bbrc.2000.2313
发表时间：
2000-03-16
影响因子：
3.1
作者：
Broderick, JB;Henshaw, TF;Broderick, WE
通讯作者：
Broderick, WE
影响因子：
15
作者：
Duffus, Benjamin R.;Ghose, Shourjo;Peters, John W.;Broderick, Joan B.
通讯作者：
Broderick, Joan B.