An electron microscope detects how vitamin A enters the cells

Using a new, high-speed camera paired with an electron microscope, scientists at Columbia University captured images of one of the smallest proteins in our cells to “see” it with a microscope.



The protein, called STRA6, is located in the membrane of our cells and is responsible for transporting vitamin A to the inside of the cell. Vitamin A is important for all mammals and is particularly important in the formation of light receptors in our eyes during the embryonic period, it is crucial for normal development.

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Before the new study, how STRA6 transports vitamin A into the cell was a mystery. Most transport proteins directly interact with the substances they carry. But STRA6 interacts with vitamin A through an intermediary protein that carries vitamin A through the blood. Continued under the cut ...



A new type of camera technology is a key element for STRA6 imaging. In combination with an electron microscope, the camera allows biologists to see tiny, previously invisible structural details of the internal mechanism of our cells.



“Now we can get closer to atomic resolution, because the new camera is much faster, and it allows us to create a film of molecules,” says Oliver Clark, Ph.D., associate research scientist at Hendrickson laboratory at Columbia University. “Even under an electron microscope, the molecules move a little, but when we photographed some kind of movement, it came out blurry. Even with such pictures, we can align the frames to create a clearer image. ”







The visualization of the molecule also depends on the painstaking biochemical procedures developed by Yantin Chen, Ph.D., adjunct, research assistant at the Mancia laboratory, to produce large amounts of protein and separate it from other cell components. “This is a very thin protein, and we had to imitate its surroundings in order to preserve its shape,” she says. It took about two years to improve the process of obtaining.

Researchers used about 70,000 individual STRA6 photos to create a 3D protein map that was used to build an atom model with the smallest detail.



Molecules while looking STRA6 is “a bit ugly,” says Dr. Clark. Even more surprising is the fact that STRA6 does not work alone, but instead is tightly linked to another protein, calmodulin, which plays a key role in the transmission of calcium signals.



Although vitamin A moves through STRA6 to enter the cell, STRA6 does not form channels in the membrane like most transport proteins. Instead, vitamin A enters the upper part of STRA6, but then a window is formed that opens directly into the cell membrane, and not into the inside of the cell.



Although it will be tested, this mechanism may be a way to protect cells from too much vitamin A. It is “actually somewhat toxic,” says Dr. Manchia. "Vitamin A traps inside the membrane can keep its amount inside the cell under control."



The new model STRA6 accelerates the understanding of cellular function and can help scientists understand how I work other, still unexplored cellular components.



Source: newsroom.cumc.columbia.edu