"Cell Research" magazine published a research result, which is expected to overturn the conclusions in the textbook. The paper shows that the actual structure of the fourth member of the organism's respiratory chain, Complex 4, is not the same as that that scientists have drawn through years of research.
The respiratory chain, as the name suggests, is related to breathing and fulfills the vital part of life activities. Each person breathes nearly 27,000 times a day, inhaling oxygen, exhaling carbon dioxide, and decomposing organic matter to release energy, and oxygen becomes water in the body. Breathing through the replacement of oxygen and carbon dioxide completes the life-supporting redox reaction. Microscopically, this universal but life-critical chemical reaction occurs in the respiratory chain of the body.
Inside the cell, you'll find an organelle called the mitochondria, which is embedded with proteins that complete the chemical reactions of life. A series of "electron transfer link" protein complexes make up the respiratory chain, delivering electrons from one end of the chain to the other, and eventually the electrons are transferred to oxygen into water. This important "chain" is interlocking, and even a slight error can lead to serious diseases and even neurological diseases such as Alzheimer's disease.
The author of the paper, Yang Maojun, a professor at the School of Life Sciences at Tsinghua University, said that the clearer the understanding of the fine structure of proteins, the more they can penetrate the life of the body. “You can clearly know which atom has a problem and design the drug to target the treatment to achieve the therapeutic effect.â€
The protein machine works and inactivates two things.
The respiratory chain is in charge of the most basic function of respiration. This chain contains hundreds of components, including 5 complexes, cytochrome C and so on.
This is a methodical protein plant, each complex can be thought of as a line on the inner membrane of the fixed mitochondria, propelling electrons to flow through changes in its conformation.
"Each complex consists of multiple different subunits. The interaction between subunits is closely related to protein conformation. Historically, there has been a period of time. As long as the structure of a single subunit or several subunits is resolved, the paper can On top magazines." Yang Maojun said.
The difficulty is that the protein machine is the same when it is working, and it is extracted from the body, and it is another when it is inactivated. It is difficult for people to observe a protein “factory†while it is operating for life.
It is a commonly used research method to remove the complex from the organism by breaking the cell, extracting the protein, and separating and purifying it, and then performing observation in the optical field. With the advancement of important observation methods such as X-ray crystallography and cryo-electron microscopy, structural biology has been developed, and people can directly obtain a conformational picture of protein crystals. However, for a series of images, people's understanding may not be the same. Only the theory that can explain all phenomena is consistent with the truth.
Uncovering the "unknown" on the dimer interface
"Since the first analysis of the complex 4 structure more than 20 years ago, the scientists have analyzed the crystal structure of more than forty complexes 4, without exception, all of the crystal structures in the complex 4 are 13+13 dimerization. Body.†Yang Maojun said that the structure of complex 4 is considered to consist of 13 subunits, and then two monomers form a dimer.
However, “When we purify the super complex, there are always some complexes 4 that will dissociate from the super complex and appear in the position of the complex monomer on the protein gel (a colloid of the isolated protein).†Yang Maojun That said, this is different from people's long-standing understanding of Composite 4.
The results of the experiment did not match the theory, so Yang Maojun decided to find out. He found that there was a significant time "watershed" in the analysis of Complex 4, and in the recently resolved supercomplex, all of the Complex 4 was monomer. Yang Maojun explained that this is because the observation method has changed. The X-ray diffraction method has been used to determine the crystal structure, and then with the development of cryo-electron microscopy, people have converted the measurement method.
Since different experimental methods will get different protein structures, what does it look like when it runs in the body?
Getting answers must be traced back to the source. Experimental data is the source of all theory. Yang Maojun decided to specifically purify the complex 4 . After half a month, the team acquired a high-resolution composite 4 structure. “After taking the density map, I carefully analyzed the subunits and found that the 13 subunits match, but there is a group of 'unknown' on the interface that originally thought to bind to another complex 4 to form a dimer. ."
He found that the focus of academic debate in recent years is whether the composite 4 is 2 × 13 subunits or 14 subunits. The focus of the debate is on a subunit called NDUFA4, which was previously thought to be a subunit of Complex 1, but as the research progressed, this subunit was often purified along with Complex 4.
Is this "unknown" just the focus of people's controversy - the sub-NDUFA4? "I immediately made a model, matched and found that the match is consistent, the group 'unknown' is the sub-unit NDUFA4." Yang Maojun said.
The error correction is derived from solid raw experimental data.
Why did this drama of "Zhang Guan Li Dai" happen? Why did the 13 subunits leave the separate subunit NDUFA4 "connected"?
"We found that the reason why the NDUFA4 subunit is 'indefinite' is because a superior detergent was added to the complex 4 in the past, and this detergent can bind a stable protein in the complex 4 protein. The cardiolipin smashed down." Yang Maojun explained, and this cardiolipin is precisely the combination of NDUFA4.
Even more coincidentally, the interface of the sub-base of "love escape" is a key interface. When it exists, it prevents the "sub-body" of the complex of 13 subunits. After it is smashed, it is given up. The position makes the dimer appear.
At this point, people's "misunderstanding" of Composite 4 has finally revealed the mystery. "The correct protein structure allows us to understand the path of electron transfer more clearly." Yang Maojun said that in the reaction center of complex 4, oxygen generates water, while another part of proton (H+) is directly pumped into the mitochondrial membrane gap. Keep it for use.
In fact, Yang Maojun defined the structure of Complex 4 a few years before the publication of the paper. Faced with the question of why the paper was published late, Yang Maojun replied, "We have to verify that it is correct through comprehensive experiments. After all, this theory has dominated the academic world for more than 20 years, and we must present a new perspective that must be rigorous."
Yang Maojun believes that the first step of original innovation is likely to be "abnormal" in scientific research. As Holmes uses a keen observation to break the case, scientists must have a keen sense of the truth embodied in the "abnormality."
"In the case of an experiment that contradicts theory, we will first find the cause from ourselves, repeat and repeat the experiment. If the result is still, try to prove that the anomaly seen is correct." Yang Maojun said that the tradition of the laboratory is Even if the experimental results obtained are in line with expectations, repeat at least three times to ensure that the results are correct. It is also these solid original experimental data that gave the Yang Maojun team a "no" conviction on the textbook. (Reporter Zhang Jiaxing)
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