A crucial enzyme in the mammalian brain seems to randomly switch on and off, according to new research reported in Nature. The V-ATPase enzyme normally generates energy to load neurotransmitters into sacs that can be transmitted to other neurons. So, the enzyme is essential for the movement of neurotransmitters, the critical signaling molecules that carry messages in the brain. V-ATPase enzymes had been thought to work continuously without becoming inactive. This research has suggested that the reality is very different, and this work may have major implications for pharmaceutical development. The research has been reported in Nature.
"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," said study leader Professor Dimitrios Stamou of the University of Copenhagen.
Our previous knowledge about this enzyme comes from research that has been conducted with enzymes that are stable and have been generated by bacteria. This new research relied on enzymes that were isolated from rat brains, however.
Neurotransmitters are put into sacs called synaptic vesicles when it's time to send a message to another neuron. This work showed that there is one V-ATPase molecule working to provide the energy for each synaptic vesicle, so when that enzyme becomes inactive, neurotransmitters are not put into that vesicle. The researchers were stunned by the findings.
"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 percent of the time these molecules are switched off," Stamou noted.
Now the researchers want to know more. For example, does this phenomenon result in many empty synaptic vesicles? And how is neuronal communication impacted? Can neurons compensate when V-ATPase enzyme shuts down, and is there another form of communication in the brain? Stamou added that the answers to these and other questions will only come with more research.
V-ATPase has other roles, including in cancer and other diseases, making it an attractive drug target. Assays that detect hits on V-ATPase are made from averages of billons of enzymes, and the effect of a drug relies on activity from enzymes that work in time, or in concert with many enzymes.
Now we understand that V-ATPase is not that kind of enzyme, noted first study author Dr. Elefterios Kosmidis, Department of Chemistry, University of Copenhagen.
"As a result, it has suddenly become critical to have methods that measure the behavior of individual V-ATPases in order to understand and optimize the desired effect of a drug."
A sensitive method created for this study can measure how drugs influence proton-pumping by a single V-ATPase molecule.