Proton transfer facilitated by ligand binding. An energetic analysis of the catalytic mechanism of Trypanosoma cruzi trans-sialidase.
Proton transfer facilitated by ligand binding. An energetic analysis of the catalytic mechanism of Trypanosoma cruzi trans-sialidase.
复制标题
配体结合促进质子转移。
DOI：
10.1021/bi101648z
复制
发表时间：
2011
期刊：
影响因子：
2.9
通讯作者：
Roitberg,AdrianE
中科院分区：
文献类型：
--
作者：
Pierdominici-Sottile,Gustavo;Roitberg,AdrianE
转唾液酸酶是克氏锥虫感染的关键酶，克氏锥虫是引起人类恰加斯病的原生动物。这种酶催化唾液酸从哺乳动物宿主细胞转移到寄生虫细胞表面，以掩盖宿主免疫系统的感染。它代表了用于治疗疾病的疗法的发展的有希望的靶标，并且已经成为广泛的结构研究的主题。精心设计的实验表明，在催化机制中形成了一个长寿命的共价中间体，并确定了一个Tyr/Glu对作为一个不寻常的催化对。这要求酪氨酸羟基质子在亲核攻击之前转移到谷氨酸的羧酸基团。由于酪氨酸和谷氨酸的溶液pKas非常不同，只有当反应环境选择性地稳定产物状态时才能完成这种转移。我们计算了质子转移在不同环境下的自由能分布，结果表明质子转移可以发生在转唾液酸酶的活性位点，但只有在底物结合之后。通过能量分解方法，我们解释了活性中心残基对反应的影响以及底物存在时反应模式的变化。这项研究代表了第一步，可以阐明我们对该反应催化机制的理解。
Trans-sialidase is a crucial enzyme for the infection ofTrypanosoma cruzi, the protozoa responsible for Chagas’ disease in humans. This enzyme catalyzes the transfer of sialic acids from mammalian host cells to parasitic cell surfaces in order to mask the infection from the host’s immune system. It represents a promising target for the development of therapeutics to treat the disease and has been subject of extensive structural studies. Elaborate experiments suggested formation of a long-lived covalent intermediate in the catalytic mechanism and identified a Tyr/Glu pair as an unusual catalytic couple. This requires that the tyrosine hydroxyl proton is transferred to the carboxylate group of glutamate before the nucleophilic attack. Since the solution pKas of tyrosine and glutamate are very different, this transfer can only be accomplished if the reaction environment selectively stabilizes the product state. We compute the free energy profile for the proton transfer in different environments, and our results indicate that it can take place in the active site of trans-sialidase, but only after substrate binding. By means of the energy decomposition method, we explain the influence that the active site residues exert on the reaction and how the pattern is changed when the substrate is present. This study represents an initial step that can shed light on our understanding of the catalytic mechanism of this reaction.