Tolbert W D, Ekstrom J L, Mathews I I, Secrist J A, Kapoor P, Pegg A E, Ealick S E
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, USA.
Biochemistry. 2001 Aug 14;40(32):9484-94. doi: 10.1021/bi010735w.
S-Adenosylmethionine decarboxylase belongs to a small class of amino acid decarboxylases that use a covalently bound pyruvate as a prosthetic group. It is an essential enzyme for polyamine biosynthesis and provides an important target for the design of anti-parasitic and cancer chemotherapeutic agents. We have determined the structures of S-adenosylmethionine decarboxylase complexed with the competitive inhibitors methylglyoxal bis(guanylhydrazone) and 4-amidinoindan-1-one-2'-amidinohydrazone as well as the irreversible inhibitors 5'-deoxy-5'-[N-methyl-N-[(2-aminooxy)ethyl]amino]adenosine, 5'-deoxy-5'-[N-methyl-N-(3-hydrazinopropyl)amino]adenosine, and the methyl ester analogue of S-adenosylmethionine. These structures elucidate residues important for substrate binding and show how those residues interact with both covalently and noncovalently bound inhibitors. S-Adenosylmethionine decarboxylase has a four-layer alphabeta betaalpha sandwich fold with residues from both beta-sheets contributing to substrate and inhibitor binding. The side chains of conserved residues Phe7, Phe223, and Glu247 and the backbone carbonyl of Leu65 play important roles in binding and positioning the ligands. The catalytically important residues Cys82, Ser229, and His243 are positioned near the methionyl group of the substrate. One molecule of putrescine per monomer is observed between the two beta-sheets but far away from the active site. The activating effects of putrescine may be due to conformational changes in the enzyme, to electrostatic effects, or both. The adenosyl moiety of the bound ligand is observed in the unusual syn conformation. The five structures reported here provide a framework for interpretation of S-adenosylmethionine decarboxylase inhibition data and suggest strategies for the development of more potent and more specific inhibitors of S-adenosylmethionine decarboxylase.
S-腺苷甲硫氨酸脱羧酶属于一小类氨基酸脱羧酶，这类酶利用共价结合的丙酮酸作为辅基。它是多胺生物合成所必需的酶，也是抗寄生虫和癌症化疗药物设计的重要靶点。我们已经确定了S-腺苷甲硫氨酸脱羧酶与竞争性抑制剂甲基乙二醛双（胍腙）和4-脒基茚满-1-酮-2'-脒基腙以及不可逆抑制剂5'-脱氧-5'-[N-甲基-N-[(2-氨基氧基)乙基]氨基]腺苷、5'-脱氧-5'-[N-甲基-N-(3-肼基丙基)氨基]腺苷和S-腺苷甲硫氨酸甲酯类似物形成的复合物的结构。这些结构阐明了对底物结合重要的残基，并展示了这些残基如何与共价和非共价结合的抑制剂相互作用。S-腺苷甲硫氨酸脱羧酶具有四层αββα三明治折叠结构，两个β折叠片层的残基都参与底物和抑制剂的结合。保守残基苯丙氨酸7、苯丙氨酸223和谷氨酸247的侧链以及亮氨酸65的主链羰基在配体的结合和定位中起重要作用。催化重要的残基半胱氨酸82、丝氨酸229和组氨酸243位于底物甲硫酰基附近。在两个β折叠片层之间观察到每个单体有一分子腐胺，但远离活性位点。腐胺的激活作用可能是由于酶的构象变化、静电作用或两者兼而有之。结合配体的腺苷部分以不寻常的顺式构象被观察到。这里报道的五个结构为解释S-腺苷甲硫氨酸脱羧酶抑制数据提供了一个框架，并提出了开发更有效、更特异性的S-腺苷甲硫氨酸脱羧酶抑制剂的策略。
