Dong Jianshu, Sasaki Daisuke, Eady Robert R, Antonyuk Svetlana V, Hasnain S Samar
Molecular Biophysics Group, Institute of Integrative Biology, Faculty of Health and Life Sciences, University of Liverpool, Liverpool L69 7ZX, England.
IUCrJ. 2018 Jun 25;5(Pt 4):510-518. doi: 10.1107/S2052252518008242. eCollection 2018 Jul 1.
There are few cases where tyrosine has been shown to be involved in catalysis or the control of catalysis despite its ability to carry out chemistry at much higher potentials (1 V NHE). Here, it is shown that a tyrosine that blocks the hydrophobic substrate-entry channel in copper-haem nitrite reductases can be activated like a switch by the treatment of crystals of nitrite reductase (NiR) with nitric oxide (NO) (-0.8 ± 0.2 V). Treatment with NO results in an opening of the channel originating from the rotation of Tyr323 away from Asp97. Remarkably, the structure of a catalytic copper-deficient enzyme also shows Tyr323 in the closed position despite the absence of type 2 copper (T2Cu), clearly demonstrating that the status of Tyr323 is not controlled by T2Cu or its redox chemistry. It is also shown that the activation by NO is not through binding to haem. It is proposed that activation of the Tyr323 switch is controlled by NO through proton abstraction from tyrosine and the formation of HNO. The insight gained here for the use of tyrosine as a switch in catalysis has wider implications for catalysis in biology.
尽管酪氨酸能够在高得多的电位（1 V NHE）下发生化学反应，但很少有案例表明它参与催化作用或对催化作用的控制。在此，研究表明，在铜-血红素亚硝酸还原酶中，阻断疏水底物进入通道的酪氨酸可像开关一样被一氧化氮（NO，-0.8±0.2 V）处理亚硝酸还原酶（NiR）晶体所激活。用NO处理会导致通道打开，这源于Tyr323从Asp97处旋转离开。值得注意的是，一种催化性缺铜酶的结构也显示，尽管不存在2型铜（T2Cu），Tyr323仍处于关闭位置，这清楚地表明Tyr323的状态不受T2Cu或其氧化还原化学的控制。研究还表明，NO的激活作用不是通过与血红素结合。有人提出，Tyr323开关的激活是由NO通过从酪氨酸夺取质子并形成HNO来控制的。在此获得的关于将酪氨酸用作催化开关的见解对生物学中的催化作用具有更广泛的意义。
