Researchers at the Louisiana State University Health Sciences Center have discovered how isolated ATP is broken down in cells, providing the first ever clear picture of the key reaction that allows living cells to function and thrive.
"ATP is the fuel of life. It is the currency of energy - the most important reservoir of chemical and mechanical energy in biological systems," explains Sunyoung Kim, the professor who led the research published in the scientific journal Journal of Biological Chemistry.
For decades, scientists have been studying and trying to fully understand this vital reaction, but until now, they have not been able to understand how proteins in living cells receive and use the energy.
In its original form, isolated ATP contains three phosphorus groups. Although it has been known for some time that in order for the proton to disintegrate, it is necessary for the third phosphorylation group to react with a hydroxide group, or a water proton that has "lost" one of its protons, it is not known what exactly removes this proton, the step that results in the release of the charge of ATP - the energy. The team chose to study a particular family of protein "machines" that break down ATP - the kinesins.
the kinesins (The entry in Wikipedia) are tiny biological machines that work similar to car engines, explains the lead researcher, and move back and forth over cellular pathways responsible for several important functions in the cell, such as cell division and transport of materials.
"We chose kinesins because they are the simplest protein "motors" known to us. Generally, proteins that break down ATP are very large and contain many moving components to perform mechanical work," explains the researcher. "The smaller and simpler the system, the more information we can gather about it in detail."
The team narrowed down further and chose the human kinesin Eg5, which is essential for cell division - both normal and abnormal - and is an interesting target for next-generation anti-cancer drugs. Suppressing the normal activity of this kinesin, by disrupting its ability to break down ATP, may be able to prevent the development of cancer, and several inhibitors of this type are now in clinical trials.
In order to gain a detailed understanding of the exact activity of the protein, the team used X-ray crystallography to produce a three-dimensional structure in which all the connections and positions of the various atoms can be observed. The challenge, however, was to capture the protein during the chain of steps in which the energy is released by forcing it to react and bind to an ATP mimic fragment, one that would not allow the removal of the phosphorylation group, and to examine the "stuck" protein in more detail.
According to one of the researchers, capturing the protein associated with the ATP-mimicking molecule is quite difficult. Prior to this research team's attempts, only three other attempts to do so had succeeded. And yet, all these successes were unsatisfactory because they failed to show exactly how the first step of the ATP breakdown occurs. Another failure lies in the fact that in most cases pure kinesin proteins were found to contain one of the breakdown products of ATP - ADP (adenosine diphosphorylated).
"We said to ourselves: 'You know what? It does not seem that one can simply insert the ATP mimic into a pure protein that is already bound to ADP. We thought we would have to get the ADP out first. This is exactly how the protein works in its natural state," says the researcher. "Thus, instead of forcing the protein to go beyond its normal sequence of steps in releasing ATP, we pulled out the ADP first and then made it react with the ATP mimic. And then, wonder and wonder - we got the desired answer." The surprising finding was that the protein uses a collection of water molecules to utilize the reaction energy.
"Prior knowledge led us to the recognition that the active substance that initiates the beginning of the ATP discharge process should be a component found in the contents of the protein, a component such as an amino acid," notes the researcher. However, it was not an amino acid at all - it was a second water molecule that pulled the proton from the first water molecule.
"Each of these water separators is connected to a different part of the protein and normally they are tightly bound to each other while connecting the two distant parts of the protein through a molecular bridge," explains the researcher. "The information we have shows that when the second water drop grabs the proton from the first water drop, this proton is transferred along this bridge. This step causes the two different parts of the protein connected by the bridge to open and then the movement of the protein is obtained." This internal movement propels the nanomachine along its trajectory, a phenomenon that allows it to perform its important activity.
"Despite the relative simplicity of the water membrane, it is still surprising and performs sophisticated operations, and I am still thrilled that we found that it is the important part of the mechanism of activity of a protein motor," says one of the researchers.
The team hopes that through a clear understanding of the mechanism of activity of biological machines, scientists will be able to better understand how different components move inside the cells, which will allow them to understand switching systems (on/off) and develop innovative drugs that can prevent and better fight various diseases.
"We believe that many of the proteins, if not all, that use the energy obtained from the breakdown of ATP are acting in the same or similar way," explains the lead researcher.
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I can understand why you chose to put a picture of her instead of a picture of the stray..:-)
Cool. I wonder if they thought of this mechanism and then proved it or if they happened to come up with it. It makes a lot of sense (although you would expect that the protein would not be satisfied with one water molecule for the purpose of exposing the hydroxide from the water and removing the proton, because if it uses several such molecules that will come closer to the active site where the water molecule is also located and then the proton withdrawal will be faster and more efficient. On the other hand, if it works with One water molecule - Dino.
exciting