Crystal structure of human spermine synthase - Implications of substrate binding and catalytic mechanism
Crystal structure of human spermine synthase - Implications of substrate binding and catalytic mechanism
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DOI：
10.1074/jbc.m710323200
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发表时间：
2008-06-06
影响因子：
4.8
通讯作者：
Plotnikov, Alexander N.
中科院分区：
文献类型：
--
作者：
Wu, Hong;Min, Jinrong;Plotnikov, Alexander N.
人精胺合成酶的两个三元络合物(EC2.5.1.22)，一个与5‘-甲硫腺苷和亚精胺，另一个与5’-甲硫腺苷和精胺，其晶体结构已被解析。他们表明，这种酶是两个相同亚基的二聚体。每个单体都有三个结构域：C-末端结构域，它包含活性部位，在结构上与亚精胺合成酶相似；中央结构域，由四条β-链组成；以及N-末端结构域，结构与S-腺苷甲硫氨酸脱羧酶结构相似，形成氨丙基供体底物。二聚化主要通过N-末端结构域之间的相互作用发生。N-末端结构域的缺失导致精胺合成酶活性的完全丧失，这表明可能需要二聚化才能发挥活性。这些结构提供了活性中心的轮廓和一个合理的催化模型。活性部位类似于亚精胺合成酶的活性部位，但有一个更大的底物结合口袋，能够容纳更长的底物。在氨丙基转移酶中保守的两个残基(Asp(201)和Asp(276))似乎在催化机制中发挥了关键作用，这一作用得到了定点突变的结果的支持。精胺合成酶中心的点5‘-甲硫腺苷结构为该产物对反应的有效抑制以及精胺合酶对精胺合酶的抑制作用比亚精胺合酶更强提供了合理的解释。还描述了追踪精胺合成酶可能的进化起源的分析。
The crystal structures of two ternary complexes of human spermine synthase (EC 2.5.1.22), one with 5'-methylthioadenosine and spermidine and the other with 5'-methylthioadenosine and spermine, have been solved. They show that the enzyme is a dimer of two identical subunits. Each monomer has three domains: a C-terminal domain, which contains the active site and is similar in structure to spermidine synthase; a central domain made up of four beta-strands; and an N-terminal domain with remarkable structural similarity to S-adenosylmethionine decarboxylase, the enzyme that forms the aminopropyl donor substrate. Dimerization occurs mainly through interactions between the N-terminal domains. Deletion of the N-terminal domain led to a complete loss of spermine synthase activity, suggesting that dimerization may be required for activity. The structures provide an outline of the active site and a plausible model for catalysis. The active site is similar to those of spermidine synthases but has a larger substrate-binding pocket able to accommodate longer substrates. Two residues (Asp(201) and Asp(276)) that are conserved in aminopropyltransferases appear to play a key part in the catalytic mechanism, and this role was supported by the results of site-directed mutagenesis. The spermine synthase center dot 5'-methylthioadenosine structure provides a plausible explanation for the potent inhibition of the reaction by this product and the stronger inhibition of spermine synthase compared with spermidine synthase. An analysis to trace possible evolutionary origins of spermine synthase is also described.