L-aspartase: new tricks from an old enzyme.
L-aspartase: new tricks from an old enzyme.
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DOI：
10.1002/9780470123201.ch7
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
Ronald E. Viola
中科院分区：
文献类型：
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作者：
Ronald E. Viola
酶L-天冬氨酸氨裂解酶（脱氨酶）催化氨基酸L-天冬氨酸的可逆脱氨，使用碳负离子机制产生富马酸和铵离子。天冬氨酸酶是已知的最具特异性的酶之一，直到最近，广泛的研究未能确定任何可替代L-天冬氨酸的替代氨基酸底物。来自不同生物体的天冬氨酸酶显示出高度的序列同源性，并且这种同源性延伸到功能相关的酶，例如II类天冬氨酸酶、天冬氨酸琥珀酸裂解酶和腺苷酸琥珀酸裂解酶。高分辨率的结构显示，该酶的单体是由三个结构域取向在一个细长的S形。由五螺旋组成的中心结构域提供功能活性四聚体中的亚基接触。活性位点位于亚基之间的裂缝中，结构和诱变研究已经确定了几个活性位点官能团。虽然这种酶的催化活性已经知道了近100年，但最近的一些研究揭示了这种合理表征的酶的一些有趣和意想不到的新特性。在某些条件下观察到的非线性动力学已被证明是由单独的调节位点的存在引起的。底物天冬氨酸也可以起到激活剂的作用，在该位点沿着所需的二价金属离子。在特定的位置上截断酶的羧基末端导致酶的催化活性的增强。还发现该区域中的截短将新的非酶生物活性引入到纤溶酶中，即通过组织纤溶酶原激活剂特异性增强纤溶酶原活化为纤溶酶的能力。即使经过世纪的研究，这种多方面的酶仍有许多方面有待探索。
The enzyme L-aspartate ammonia-lyase (aspartase) catalyzes the reversible deamination of the amino acid L-aspartic acid, using a carbanion mechanism to produce fumaric acid and ammonium ion. Aspartase is among the most specific enzymes known with extensive studies failing, until recently, to identify any alternative amino acid substrates that can replace L-aspartic acid. Aspartases from different organisms show high sequence homology, and this homology extends to functionally related enzymes such as the class II fumarases, the argininosuccinate and adenylosuccinate lyases. The high-resolution structure of aspartase reveals a monomer that is composed of three domains oriented in an elongated S-shape. The central domain, comprised of five-helices, provides the subunit contacts in the functionally active tetramer. The active sites are located in clefts between the subunits and structural and mutagenic studies have identified several of the active site functional groups. While the catalytic activity of this enzyme has been known for nearly 100 years, a number of recent studies have revealed some interesting and unexpected new properties of this reasonably well-characterized enzyme. The non-linear kinetics that are seen under certain conditions have been shown to be caused by the presence of a separate regulatory site. The substrate, aspartic acid, can also play the role of an activator, binding at this site along with a required divalent metal ion. Truncation of the carboxyl terminus of aspartase at specific positions leads to an enhancement of the catalytic activity of the enzyme. Truncations in this region also have been found to introduce a new, non-enzymatic biological activity into aspartase, the ability to specifically enhance the activation of plasminogen to plasmin by tissue plasminogen activator. Even after a century of investigation there are clearly a number of aspects of this multifaceted enzyme that remain to be explored.