Summary: V-ATPase, a vital enzyme that enables neurotransmission, is able to turn on and off randomly, even when taking breaks of several hours.
Source: University of Copenhagen
In a new breakthrough to better understand the mammalian brain, researchers from the University of Copenhagen have made an incredible discovery. Namely, a vital enzyme that activates brain signals turns on and off randomly, even taking hours of “work breaks.”
These discoveries could have a major impact on our understanding of the brain and on the development of pharmaceutical products.
Today, the discovery is on the cover of Nature.
Millions of neurons constantly exchange messages to shape our thoughts and memories and allow us to move our bodies at will. When two neurons meet to exchange a message, neurotransmitters are transported from one neuron to the other using a unique enzyme.
This process is crucial for neural communication and the survival of all complex organisms. Until now, researchers around the world believed that these enzymes were active at all times to continuously convey essential signals. But it is far from being the case.
Using an innovative method, researchers from the Department of Chemistry at the University of Copenhagen studied the enzyme closely and found that its activity turns on and off at random intervals, which contradicts our prior understanding.
“This is the first time anyone has studied these mammalian brain enzymes, one molecule at a time, and we are impressed with the results. Contrary to popular belief, and unlike many other proteins, these enzymes could stop function for minutes or hours. Yet the brains of humans and other mammals are miraculously able to function,” says Professor Dimitrios Stamou, who led the study at the Department of Chemistry’s Center for Geometrically Modified Cellular Systems. from the University of Copenhagen.
Until now, such studies were carried out with very stable enzymes derived from bacteria. Using the new method, the researchers studied mammalian enzymes isolated from the brains of rats for the first time.
Today, the study is published in Nature.
Enzyme switching may have profound implications for neural communication
Neurons communicate using neurotransmitters. To transfer messages between two neurons, neurotransmitters are first pumped into small membrane bladders (called synaptic vesicles). The bladders act as containers that store neurotransmitters and only release them between the two neurons when it is time to deliver a message.
The central enzyme in this study, known as V-ATPase, is responsible for providing energy to pump neurotransmitters into these containers. Without it, neurotransmitters wouldn’t be pumped into the containers, and the containers couldn’t transmit messages between neurons.
But the study shows that in each container, there is only one enzyme; when this enzyme shuts down, there would be no more energy to drive the loading of neurotransmitters into the containers. This is an entirely new and unexpected discovery.
“It is almost incomprehensible that the extremely critical process of loading neurotransmitters into containers is delegated to a single molecule per container. Especially when we see that 40% of the time these molecules are extinct”, specifies Professor Dimitrios Stamou.
These findings raise many intriguing questions:
“Does the closure of the containers’ power source mean that many of them are effectively empty of neurotransmitters?” Would a large fraction of empty containers have a significant impact on communication between neurons? If so, could this be a “problem” that neurons have evolved to work around, or could this be a whole new way of encoding important information in the brain? Only time will tell,” he says.
A revolutionary method to screen drugs for V-ATPase
The V-ATPase enzyme is an important drug target because it plays a critical role in cancer, cancer metastasis, and several other life-threatening diseases. Thus, V-ATPase is a lucrative target for anti-cancer drug development.
Existing assays to screen drugs for 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 works consistently over time or when enzymes work together in large numbers.
“However, we now know that neither is necessarily true for the V-ATPase. As a result, it has suddenly become essential to have methods that measure the behavior of individual V-ATPases in order to understand and to optimize the desired effect of a drug,” explains the first author of the paper, Dr. Elefterios Kosmidis, Department of Chemistry, University of Copenhagen, who led the laboratory experiments.
The method developed here is the first ever capable of measuring the effects of drugs on the proton pumping of single V-ATPase molecules. It can detect currents over a million times smaller than the gold standard patch clamp method.
V-ATPase Enzyme Facts:
- V-ATPases are enzymes that break down ATP molecules to pump protons across cell membranes.
- They are present in all cells and are essential for controlling pH/acidity inside and/or outside cells.
- In neuronal cells, the proton gradient established by V-ATPases provides energy to load neurochemical messengers called neurotransmitters into synaptic vesicles for later release at synaptic connections.
About this neuroscience research news
Author: Press office
Source: University of Copenhagen
Contact: Press office – University of Copenhagen
Image: Image is in public domain
Original research: Access closed.
“Regulation of mammalian brain V-ATPase by ultra-slow mode switching” by Dimitrios Stamou et al. Nature
Regulation of mammalian brain V-ATPase by ultra-slow mode switching
Vacuolar-type adenosine triphosphatases (V-ATPases) are electrogenic rotating mechanoenzymes structurally related to F-type ATP synthases. They hydrolyze ATP to establish electrochemical proton gradients for a plethora of cellular processes.
In neurons, the loading of all neurotransmitters into synaptic vesicles is stimulated by approximately one molecule of V-ATPase per synaptic vesicle. To shed light on this authentic single-molecule biological process, we investigated electrogenic proton pumping by unique mammalian brain V-ATPases in single synaptic vesicles.
Here, we show that V-ATPases do not continuously pump over time, as suggested by the observation of rotation of bacterial homologs and the hypothesis of tight ATP-proton coupling.
Instead, they stochastically switch between three ultra-long-lived modes: proton pumping, idle, and proton leak. Notably, direct observation of pumping revealed that physiologically relevant ATP concentrations do not regulate intrinsic pumping rate.
ATP regulates the activity of V-ATPase by the probability of switching the proton pumping mode. In contrast, electrochemical proton gradients regulate the pumping rate and the switching of pumping and idle modes.
A direct consequence of mode switching is stochastic on-off fluctuations in the electrochemical gradient of synaptic vesicles which should introduce stochasticity into the proton-driven secondary active charge of neurotransmitters and thus may have important implications for neurotransmission.
This work reveals and highlights the mechanistic and biological importance of ultra-slow mode switching.
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