动物实验,动物线粒体 z-bo 2020-10-12 416

　　Mitochondria are the energy factories of our cells. The energy produced by mitochondria supports life. What is important is a huge molecular proton pump called Complex I (Complex I). It initiates a series of reactions and establishes a proton gradient to promote the production of ATP. Complex I plays a central role, but the mechanism of its proton transport across the membrane is still unclear.

　　Now, in a new study, Leonid Sazanov of the Austrian Academy of Science and Technology and his team have solved the mystery of how complex I works: combining its constitutive changes and static waves to transform protons into a mitochondrial matrix. To move it.

　　Complex I is the first enzyme in the respiratory chain. The respiratory chain is composed of a series of protein complexes in the inner mitochondrial membrane, responsible for most of the cell's energy production. In the respiratory chain, the three membrane proteins establish a proton gradient to move protons from the cytoplasm to the mitochondrial matrix. The energy that drives this process mainly comes from electron transfer between NADH molecules (from the food we eat) and breathing oxygen. ATP synthase is the last protein in the respiratory chain and uses this proton gradient to produce ATP.

　　Complex I not only plays a central role in life, but also very interesting in terms of scale. The molecular weight of eukaryotic complex I is 1 megadalton, which is one of the largest membrane proteins. This size also makes it difficult to study Compound I. After analyzing the structure of relatively simple bacterial enzymes in 2013, in 2016, Sazanov's team took the lead in determining the structure of the mammalian I complex. However, the mechanism by which complex I moves protons across the membrane is controversial. Sazhanov said: "There is a view that a part of the complex I acts as a piston to open and close the proton channel. Another view is that the amino acid residues in the center of the complex I act as a driver. "

　　Another one, I found it is already configured. In the hydrophilic arm, electrons are transferred from NADH to the hydrophobic electron carrier quinone. The membrane arm is where protons are transported. There are three structures associated with the anti-porter subsystem. One subsystem contains a quinone coupling cavity. In this cavity bound to quinone, complex I transfers two electrons to quinone in each catalytic cycle, and quinone further transfers electrons to complex III and complex IV. However, since these antiporter-like subunits are too far away from the quinone binding cavity, how does the interaction between electrons and quinone move the four protons of each catalytic cycle across the membrane? The mystery is. To solve this problem, Sazanov's team performed cryo-electron microscopy of compound I in sheep. Through a series of efforts, the first author of the paper, Domen Kampjut, a PhD student in Sasanov’s team, solved the structure of 23 different complexes obtained under different conditions. By adding NADH and Kinon, you can capture the Complex I image at work and change the conformation between the two main states while working. Because of its high resolution, it can identify water molecules in proteins. This is the key to realizing proton transfer. They provide a way for many water molecules on the central axis of the membrane arms to make protons jump between polar amino acid residues and water, thereby forming channels along and across the membrane.

　　But only in the subsystem furthest from Kinon does the proton jump over the membrane. The other two subsystems provide the bond between the furthest subsystem and the quinone. When the quinone binding cavity "waits" for the quinone to arrive, the spiral blocks the water filament on the central axis of the membrane arm. When the quinone binds to the quinone binding cavity, the conformation of the protein around the region changes drastically, causing the spiral to rotate. At this time, the water pipe connects all the membrane subsystems of complex I, and the two protons move to the quinone to complete the reduction of the quinone. An important part of this mechanism is the static wave, in which a charge is generated near the first invertor and triggers the interaction between the charged amino acid residues. Static waves propagate along these antiporters, four in total.

　　Sazanov explains: "We have discovered a new and unexpected mechanism that works in complex I. The combination of conformational changes and static waves promotes the transfer of protons through the membrane. This seems a bit excessive, but it may be useful. . This mechanism is still very robust."