Big discovery about mammalian brains surprises researchers

Summary: V-ATPase, a vital enzyme that enables neurotransmission, is able to turn itself on and off randomly, even after hours of rest.

Source: University of Copenhagen

In a new breakthrough to understanding more about the mammalian brain, researchers at the University of Copenhagen have made an incredible discovery. Namely, a vital enzyme that enables brain signals turns on and off randomly, even taking hours-long “breaks from work.”

These findings may have a major impact on our understanding of the brain and the development of pharmaceutical products.

Today the discovery is on the cover of Nature.

Millions of neurons are constantly exchanging messages to shape 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 another with the help of a single enzyme.

This process is crucial for neuronal communication and survival of all complex organisms. Until now, researchers around the world thought that these enzymes were always active to continuously transmit essential signals. But this is far from the case.

Using an innovative method, researchers from the Department of Chemistry at the University of Copenhagen closely studied the enzyme and found that its activity turns on and off at random intervals, which contradicts our previous understanding.

“This is the first time anyone has studied these mammalian brain enzymes one molecule at a time and we are amazed by the result. Contrary to popular belief and unlike many other proteins, these enzymes may stop working for minutes or hours. However, the brains of humans and other mammals are miraculously capable of functioning,” says Professor Dimitrios Stamou, who led the study at the Center for Geometric Engineering Cellular Systems in the Department of Chemistry at the University of Copenhagen .

Until now, such studies have been conducted with very stable bacterial enzymes. Using the new method, the researchers studied mammalian enzymes isolated from the brains of rats for the first time.

Today the study was published on Nature.

Enzyme switching may have far-reaching implications for neuronal communication

Neurons communicate via neurotransmitters. To transfer messages between two neurons, neurotransmitters are first pumped into small membrane-bound vesicles (called synaptic vesicles). The bladders act as containers that store neurotransmitters and only release them between the two neurons when it’s time to deliver a message.

The central enzyme in this study, known as V-ATPase, is responsible for supplying energy for the neurotransmitter pumps in these canisters. Without it, neurotransmitters wouldn’t be pumped into the bins, and the bins wouldn’t be able to transmit messages between neurons.

But the study shows that there is only one enzyme in each container; when this enzyme shuts down, there would be no more energy to drive the loading of neurotransmitters into the containers. This is a completely new and unexpected discovery.

“It is almost incomprehensible that the extremely critical process of loading neurotransmitters into 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.

The cover illustration shows vacuolar-type adenosine triphosphatases (V-ATPases, large blue structures) on a nerve cell synaptic vesicle in the mammalian brain. Image: C. Kutzner, H. Grubmüller and R. Jahn/Max Planck Institute for Multidisciplinary Sciences. Credits: C. Kutzner, H. Grubmüller and R. Jahn/Max Planck Institute for Multidisciplinary Sciences.

These results raise many intriguing questions:

“Does the interruption of the energy source of the containers mean that many of them are really devoid of neurotransmitters? Would a large fraction of empty containers have a significant impact on the communication between neurons? If so, would it be a “problem” that neurons have evolved to work around, or could it be an entirely new way of encoding important information in the brain? Only time will tell,” she says.

A revolutionary method for drug screening for V-ATPase

The V-ATPase enzyme is an important drug target because it plays a critical role in cancer, cancer metastasis, and many other life-threatening diseases. Therefore, V-ATPase is a lucrative target for anticancer drug development.

Existing drug screening tests for V-ATPase rely on the simultaneous averaging of 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 V-ATPase. As a result, it has suddenly become crucial to have methods that measure the behavior of individual V-ATPases in order to understand and optimize a drug’s desired effect,” says 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 drug effects on the proton pumping of individual V-ATPase molecules. It is capable of detecting currents more than a million times lower than the gold standard patch clamp method.

About V-ATPase Enzyme:

See also

This shows a brain
  • V-ATPases are enzymes that break down ATP molecules to pump protons across cell membranes.
  • They are found in all cells and are essential for pH/acidity control within and/or outside cells.
  • In neuronal cells, the proton gradient established by V-ATPases provides energy for the loading of neurochemical messengers called neurotransmitters into synaptic vesicles for subsequent release to synaptic connections.

About this neuroscience research news

Author: Press office
Source: University of Copenhagen
Contact: Press Office – University of Copenhagen
Image: Image is public domain

Original research: Access closed.
“V-ATPase regulation of the mammalian brain through ultra-slow mode switching” by Dimitrios Stamou et al. Nature


Abstract

Regulation of mammalian brain V-ATPase through ultraslow mode switching

Vacuolar-type adenosine triphosphatases (V-ATPases) are electrogenic rotary 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 the synaptic vesicles is energized by approximately one molecule of V-ATPase per synaptic vesicle. To shed light on this bona fide single-molecule biological process, we investigated electrogenic proton pumping by individual mammalian brain V-ATPases into individual synaptic vesicles.

Here we show that V-ATPases do not pump continuously over time, as suggested by observing the rotation of bacterial homologues and assuming strict ATP-proton coupling.

Instead, they stochastically switch between three ultralong-lived modes: proton pumping, idle, and proton leaking. In particular, direct observation of pumping revealed that physiologically relevant concentrations of ATP do not regulate the intrinsic rate of pumping.

ATP regulates V-ATPase activity through the probability of proton pumping mode switching. Conversely, electrochemical proton gradients regulate the pumping rate and the switching of pumping and idle modes.

A direct consequence of mode switching are all-or-nothing stochastic fluctuations in the electrochemical gradient of synaptic vesicles that should introduce stochasticities in the proton-driven secondary active loading of neurotransmitters and could thus have important implications for neurotransmission.

This work reveals and underlines the mechanistic and biological importance of ultra-slow mode switching.

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