Guy Jodie L, Jackson Richard M, Jensen Hanne A, Hooper Nigel M, Turner Anthony J
School of Biochemistry and Microbiology, University of Leeds, UK.
FEBS J. 2005 Jul;272(14):3512-20. doi: 10.1111/j.1742-4658.2005.04756.x.
Angiotensin-converting enzyme-2 (ACE2) may play an important role in cardiorenal disease and it has also been implicated as a cellular receptor for the severe acute respiratory syndrome (SARS) virus. The ACE2 active-site model and its crystal structure, which was solved recently, highlighted key differences between ACE2 and its counterpart angiotensin-converting enzyme (ACE), which are responsible for their differing substrate and inhibitor sensitivities. In this study the role of ACE2 active-site residues was explored by site-directed mutagenesis. Arg273 was found to be critical for substrate binding such that its replacement causes enzyme activity to be abolished. Although both His505 and His345 are involved in catalysis, it is His345 and not His505 that acts as the hydrogen bond donor/acceptor in the formation of the tetrahedral peptide intermediate. The difference in chloride sensitivity between ACE2 and ACE was investigated, and the absence of a second chloride-binding site (CL2) in ACE2 confirmed. Thus ACE2 has only one chloride-binding site (CL1) whereas ACE has two sites. This is the first study to address the differences that exist between ACE2 and ACE at the molecular level. The results can be applied to future studies aimed at unravelling the role of ACE2, relative to ACE, in vivo.
血管紧张素转换酶2（ACE2）可能在心脏肾脏疾病中发挥重要作用，并且它也被认为是严重急性呼吸综合征（SARS）病毒的细胞受体。最近解析出的ACE2活性位点模型及其晶体结构突出了ACE2与其对应物血管紧张素转换酶（ACE）之间的关键差异，这些差异导致了它们对底物和抑制剂敏感性的不同。在本研究中，通过定点诱变探索了ACE2活性位点残基的作用。发现精氨酸273对于底物结合至关重要，其替换会导致酶活性丧失。虽然组氨酸505和组氨酸345都参与催化作用，但在四面体肽中间体形成过程中作为氢键供体/受体的是组氨酸345而非组氨酸505。研究了ACE2和ACE之间氯离子敏感性的差异，并证实ACE2中不存在第二个氯离子结合位点（CL2）。因此，ACE2只有一个氯离子结合位点（CL1），而ACE有两个位点。这是第一项在分子水平上探讨ACE2和ACE之间存在差异的研究。这些结果可应用于未来旨在阐明ACE2相对于ACE在体内作用的研究。
