Summary: V-ATPase, a vital enzyme that enables neurotransmission, can randomly turn on and off, even taking hours-long breaks.
Font: University of Copenhagen
In a new breakthrough to understand more about the mammalian brain, researchers at the University of Copenhagen have made an incredible discovery. Namely, a vital enzyme that allows brain signals to turn on and off at random, even taking hours-long “breaks from work.”
These findings may have a major impact on our understanding of the brain and the development of pharmaceuticals.
Today, the discovery is on the cover of Nature.
Millions of neurons constantly send messages to each other 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 unique enzyme.
This process is crucial for neural communication and the survival of all complex organisms. Until now, researchers around the world thought that these enzymes were active at all times 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 studied the enzyme closely and found that its activity turns 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 amazed with the result. Contrary to popular belief, and unlike many other proteins, these enzymes could stop working for minutes or hours. Still, the brains of humans and other mammals can function miraculously,” says Professor Dimitrios Stamou, who led the study from the Center for Geometrically Engineered Cellular Systems in the Department of Chemistry at the University of Copenhagen.
Until now, these studies were carried out with very stable enzymes from bacteria. Using the new method, the researchers are investigating mammalian enzymes isolated from rat brains for the first time.
Today, the study is published in Nature.
Enzyme change may have far-reaching implications for neural communication
Neurons communicate using neurotransmitters. To transfer messages between two neurons, neurotransmitters are first pumped into tiny bladders of membrane (called synaptic vesicles). The bladders act as containers that store the neurotransmitters and release them between the two neurons only when it is time to send a message.
The central enzyme in this study, known as V-ATPase, is responsible for supplying the energy for the neurotransmitter pumps in these containers. Without it, the neurotransmitters would not be pumped into the containers, and the containers would not be able to transmit messages between neurons.
But the study shows that in each container there is only one enzyme; when this enzyme is turned off, there will be no more energy to drive the load of neurotransmitters into the bins. 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 a single molecule per container. Especially when we find that 40% of the time these molecules are off”, says Professor Dimitrios Stamou.
These findings raise many intriguing questions:
“Does turning off the power supply to the containers mean that many of them are actually depleted of neurotransmitters? Would a large fraction of empty containers significantly affect communication between neurons? If so, was that a ‘problem’ that neurons evolved to circumvent, or could it be an entirely new way of encoding important information in the brain? Only time will tell,” she says.
A revolutionary method to screen drugs for the 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. Therefore, the V-ATPase is a lucrative target for anticancer drug development.
Existing assays to detect V-ATPase in drugs are based on simultaneously averaging the signal of billions of enzymes. Knowing the average effect of a drug is sufficient whenever an enzyme works constantly over time or when enzymes work together in large amounts.
“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 optimize the desired effect of a drug,” says the paper’s first author, Dr. Elefterios Kosmidis, Department of Chemistry. from the University of Copenhagen, who spearheaded the experiments in the lab.
The method developed here is the first that can measure the effects of drugs on the proton pumping of individual V-ATPase molecules. It can detect currents more than a million times smaller than the standard patch clamp method.
Facts about the V-ATPase enzyme:
See also
- 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 controlling pH/acidity inside and/or outside of cells.
- In neuronal cells, the proton gradient established by V-ATPases provides energy to load neurochemical messengers called neurotransmitters into synaptic vesicles for subsequent release at synaptic junctions.
About this neuroscience research news
Author: press office
Font: University of Copenhagen
Contact: Press Office – University of Copenhagen
Image: The image is in the public domain.
original research: closed access.
“Regulation of Mammalian Brain V-ATPase via Creep Mode Switchingby Dimitrios Stamou et al. Nature
Summary
Regulation of Mammalian Brain V-ATPase via Creep 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 synaptic vesicles is powered by approximately one V-ATPase molecule 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 looking at the turnover of bacterial homologues and assuming tight ATP-proton coupling.
Instead, they stochastically switch between three ultra-long-lived modes: proton pumping, quiescent, and proton leaking. In particular, direct observation of pumping revealed that physiologically relevant concentrations of ATP do not regulate the intrinsic pump rate.
ATP regulates the activity of V-ATPase through the probability of switching the mode of proton pumping. Conversely, electrochemical proton gradients regulate the rate of pumping and the switching between pumped and quiescent modes.
A direct consequence of mode switching is stochastic all-or-none fluctuations in the electrochemical gradient of synaptic vesicles that would be expected to introduce stochasticity in the proton-driven secondary active charging of neurotransmitters and thus may have important implications for neurotransmission.
This work reveals and emphasizes the mechanical and biological importance of ultraslow mode switching.
