The most abundant molecule in cell membranes is the lipid phosphatidylcholine (PC, commonly known as lecithin); accordingly, the enzymes responsible for synthesizing it are essential. Research published in the May 4 issue of the Journal of Biological Chemistry used computer simulations to gain insights into how one of these enzymes activates and shuts off PC production. These results could help researchers understand why small changes in this enzyme can lead to conditions like blindness and dwarfism.
Rosemary Cornell, a professor of molecular biology and biochemistry at Simon Fraser University in Canada, studies the enzyme CTP:phosphocholine cytidylyltransferase, or CCT. CCT sets the rate of PC production in cells by binding to cell membranes with low PC content.
CCT is a key enzyme that maintains a balanced composition of cell membrane phospholipids. Image highlights the dynamics of a portion of the enzyme CCT that is essential for regulation of its functions. The molecular dynamics was explored in a collaboration between the Cornell and Tieleman labs using computational methods.
Credit: Mohsen Ramezanpour and Jaeyong Lee
When bound to membranes, the CCT enzyme changes shape in a way that allows it to carry out the key rate-limiting step in PC synthesis. When the amount of PC making up the membrane increases, the CCT falls off the membrane, and PC production ceases.
"The membrane is this big macromolecular array with lots of different molecules in it," Cornell said. "How does this enzyme recognize that 'Oh, I should slow down because the PC content of the membrane is getting too high?'"
Cornell and her project team - a collaboration with Peter Tieleman and graduate student, Mohsen Ramezanpour at the University of Calgary and Jaeyong Lee and Svetla Taneva, research associates at SFU - thought that the answer must have to do with the dynamic changes in shape that the enzyme undergoes when it binds to a membrane.
But these changes are difficult to capture with traditional structural biology methods like x-ray crystallography, which take a static snapshot of molecules. Instead, the team used computational simulations of molecular dynamics, which use information about the forces between every individual atom in a molecule to calculate the trajectories of the enzyme's moving parts.
"What it looks like (when you visualize the output) is your big molecule dancing in front of your eyes," Cornell said. "We set up the molecular dynamics simulation not once, not twice, but 40 different (times). It took months and months just to do the computational parts and even more months trying to analyze the data afterward. We actually spent a lot of time once we got the data just looking on the screen at these dancing molecules."
The simulated dance of the CCT molecule showed that when the M-domain, the section of the enzyme that typically binds to the membrane, detaches from a membrane, it snags the active site of the enzyme, preventing it from carrying out its reaction. When the snagging segment was removed from the simulation, the team saw a dramatic bending motion in the docking site for the snagging element, and speculated that this bending would create a better enzyme active site for catalyzing the reaction when attached to a membrane. The team confirmed these mechanisms using biochemical laboratory experiments.
Interestingly, previous genetic studies had shown that mutations in the gene encoding CCT are responsible for rare conditions like spondylometaphyseal dysplasia with cone-rod dystrophy, which causes severe impairments in bone growth and vision, but it was unknown how these changes in the enzyme could lead to such dramatic consequences. Cornell hopes that understanding how the enzyme works could help researchers find out.
"If you have just one small change in CCT, then how is that going to make this whole process of synthesizing PC defective?" Cornell asks. "That's what we're studying right now."
The study was funded by the Canadian Institutes for Health Research.
About the Journal of Biological Chemistry
JBC is a weekly peer-reviewed scientific journal that publishes research "motivated by biology, enabled by chemistry" across all areas of biochemistry and molecular biology. The read the latest research in JBC, visit http://www.
About the American Society for Biochemistry and Molecular Biology
The ASBMB is a nonprofit scientific and educational organization with more than 12,000 members worldwide. Most members teach and conduct research at colleges and universities. Others conduct research in various government laboratories, at nonprofit research institutions and in industry. The Society's student members attend undergraduate or graduate institutions. For more information about ASBMB, visit http://www.
Sasha Mushegian | EurekAlert!
New image of a cancer-related enzyme in action helps explain gene regulation
05.06.2020 | Penn State
Protecting the Neuronal Architecture
05.06.2020 | Universität Heidelberg
Humans rely dominantly on their eyesight. Losing vision means not being able to read, recognize faces or find objects. Macular degeneration is one of the major...
In meningococci, the RNA-binding protein ProQ plays a major role. Together with RNA molecules, it regulates processes that are important for pathogenic properties of the bacteria.
Meningococci are bacteria that can cause life-threatening meningitis and sepsis. These pathogens use a small protein with a large impact: The RNA-binding...
An analysis of more than 200,000 spiral galaxies has revealed unexpected links between spin directions of galaxies, and the structure formed by these links...
Two prominent X-ray emission lines of highly charged iron have puzzled astrophysicists for decades: their measured and calculated brightness ratios always disagree. This hinders good determinations of plasma temperatures and densities. New, careful high-precision measurements, together with top-level calculations now exclude all hitherto proposed explanations for this discrepancy, and thus deepen the problem.
Hot astrophysical plasmas fill the intergalactic space, and brightly shine in stellar coronae, active galactic nuclei, and supernova remnants. They contain...
In living cells, enzymes drive biochemical metabolic processes enabling reactions to take place efficiently. It is this very ability which allows them to be used as catalysts in biotechnology, for example to create chemical products such as pharmaceutics. Researchers now identified an enzyme that, when illuminated with blue light, becomes catalytically active and initiates a reaction that was previously unknown in enzymatics. The study was published in "Nature Communications".
Enzymes: they are the central drivers for biochemical metabolic processes in every living cell, enabling reactions to take place efficiently. It is this very...
19.05.2020 | Event News
07.04.2020 | Event News
06.04.2020 | Event News
05.06.2020 | Life Sciences
05.06.2020 | Physics and Astronomy
05.06.2020 | Life Sciences