Picobiology Institute, Graduate School of Life Science, University of Hyogo, 3-2-1 Kouto, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan.
RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.
Sci Adv. 2017 Jul 14;3(7):e1603042. doi: 10.1126/sciadv.1603042. eCollection 2017 Jul.
Bovine cytochrome c oxidase (CcO), a 420-kDa membrane protein, pumps protons using electrostatic repulsion between protons transferred through a water channel and net positive charges created by oxidation of heme (Fe ) for reduction of O at heme (Fe ). For this process to function properly, timing is essential: The channel must be closed after collection of the protons to be pumped and before Fe oxidation. If the channel were to remain open, spontaneous backflow of the collected protons would occur. For elucidation of the channel closure mechanism, the opening of the channel, which occurs upon release of CO from CcO, is investigated by newly developed time-resolved x-ray free-electron laser and infrared techniques with nanosecond time resolution. The opening process indicates that Cu senses completion of proton collection and binds O before binding to Fe to close the water channel using a conformational relay system, which includes Cu, heme , and a transmembrane helix, to block backflow of the collected protons.
牛细胞色素 c 氧化酶（CcO）是一种 420kDa 的膜蛋白，利用质子通过水通道传递时所产生的静电力排斥作用以及通过氧化血红素（Fe ）为还原态氧（O）产生的净正电荷来泵送质子。为了使这个过程正常运行，时机至关重要：在收集要泵送的质子之后，在 Fe 氧化之前，通道必须关闭。如果通道保持打开状态，收集到的质子会自发回流。为了阐明通道关闭机制，新开发的纳秒时间分辨率的时间分辨 X 射线自由电子激光和红外技术用于研究 CcO 释放 CO 时通道的打开过程。打开过程表明，Cu 在与 Fe 结合之前，通过构象接力系统来感知质子收集的完成，并结合 O 以关闭水通道，该系统包括 Cu、血红素和跨膜螺旋，以阻止收集到的质子回流。
