The human brain is the most complex and poorly understood biological structure known to man. Our human brain is relatively large for our body size and wrinkled in comparison to other animals’ brains. Across species, brain size and wrinkle number correlate with intelligence.
University of Copenhagen researchers have made an incredible discovery in their quest to learn more about the mammalian brain. A vital enzyme that allows brain signals to be transmitted is randomly turning on and off, even taking hours-long “breaks from work.” These discoveries could have a significant impact on our understanding of the brain and the development of pharmaceuticals. The discovery is featured on the cover of Nature.
Millions of neurons are constantly communicating with one another, shaping thoughts and memories and allowing us to move our bodies at will. Neurotransmitters are transported from one neuron to another by a unique enzyme when two neurons meet to exchange a message.
This process is necessary for neuronal communication as well as the survival of all complex organisms. Until now, researchers all over the world assumed that these enzymes were constantly active, transmitting vital signals. However, this is not the case.
It is nearly incomprehensible that the extremely critical process of loading neurotransmitters in containers is delegated to only one molecule per container. Especially when we find that 40% of the time these molecules are switched off.
Professor Dimitrios Stamou
Using a novel method, researchers from the Department of Chemistry at the University of Copenhagen closely examined the enzyme and discovered that its activity switches on and off at random intervals, contradicting our previous understanding.
“This is the first time anyone has studied these mammalian brain enzymes one molecule at a time, and we are awed by the result. Contrary to popular belief, and unlike many other proteins, these enzymes could stop working for minutes to hours. Still, the brains of humans and other mammals are miraculously able to function,” says Professor Dimitrios Stamou, who led the study from the center for Geometrically Engineered Cellular Systems at the University of Copenhagen’s Department of Chemistry.
Until now, such studies were carried on with very stable enzymes from bacteria. Using the new method, the researchers investigated mammalian enzymes isolated from rats’ brains for the first time. Today, the study is published and placed on the cover of the scientific journal Nature.
Enzyme-switching may have far-reaching implications for neuronal communication
Neurotransmitters help neurons communicate. Neurotransmitters are first pumped into small membrane bladders to transfer messages between two neurons (called synaptic vesicles). The bladders function as containers that store neurotransmitters and release them between the two neurons only when it is time to deliver a message.
The central enzyme in this study, known as V-ATPase, is in charge of supplying energy to the neurotransmitter pumps in these containers. Without it, neurotransmitters would not be pumped into the containers, and the containers would be unable to transmit messages between neurons. However, the study shows that each container contains only one enzyme; if this enzyme is turned off, there is no longer any energy to drive the loading of neurotransmitters into the containers. This is an entirely new and unexpected discovery.
“It is nearly incomprehensible that the extremely critical process of loading neurotransmitters in containers is delegated to only one molecule per container. Especially when we find that 40% of the time these molecules are switched off,” says Professor Dimitrios Stamou.
These findings raise many intriguing questions:
“Does shutting down the energy source of the containers mean many of them are indeed empty of neurotransmitters? Would a large fraction of empty containers significantly impact the communication between neurons? If so, would that be a “problem” that neurons evolved to circumvent, or could it possibly be an entirely new way to encode important information in the brain? Only time will tell,” he says.
A revolutionary method to screen drugs for the V-ATPase
The V-ATPase enzyme is an important drug target because it plays critical roles in cancer, cancer metastasis, and several other life-threatening diseases. Thus, the V-ATPase is a lucrative target for anticancer drug development.
Existing assays to screen drugs for the V-ATPase are based on simultaneously averaging the signal from billions of enzymes. Knowing the average effect of a drug is sufficient as long as an enzyme constantly works in time or when enzymes work together in large numbers.
“However, we now know that neither of these statements is necessarily true for V-ATPase. As a result, methods for measuring the behavior of individual V-ATPases have suddenly become critical in order to understand and optimize the desired effect of a drug” Dr. Elefterios Kosmidis, Department of Chemistry, University of Copenhagen, who led the experiments in the lab, is the article’s first author.
The method developed here is the first to be able to measure drug effects on the proton-pumping of single V-ATPase molecules. It detects currents that are more than a million times smaller than the gold-standard patch clamp method.
Facts about the V-ATPase enzyme:
- V-ATPases are enzymes that break down ATP molecules to pump protons across cellular membranes.
- They are found in all cells and are essential for controlling the pH/acidity inside and/or outside cells.
- In neuronal cells, the proton gradient established by V-ATPases provides energy for loading neurochemical messengers called neurotransmitters into synaptic vesicles for subsequent release at synaptic connections.
