Deep inside the brain, tiny gaps called nodes of Ranvier act like relay stations, helping electrical signals zoom through nerve fibers at high speed. Now, scientists at Gifu University in Japan have discovered that special sugar molecules are essential for keeping those relay stations working properly.
The research, published in the journal Communications Biology on July 13, focuses on a type of sugar called O-mannose glycans. These molecules coat key proteins in the brain, influencing how those proteins behave. While scientists knew these sugars were abundant in the brain, nobody understood exactly what they did—until now.
"Defects in O-mannose glycans have previously been associated with neurological disorders, but exactly what these sugar structures do under normal conditions has yet to be fully understood," said Yasuhiko Kizuka, a professor at Gifu University's Institute for Glyco-core Research who led the study.
To solve the mystery, Kizuka and his team studied laboratory mice that were genetically modified to lack MGAT5B, an enzyme that helps build branched sugar structures on proteins in the brain. The researchers then measured how this loss affected the mice's nerve cells and behavior.
The results were striking. Mice without MGAT5B developed abnormally wide nodes of Ranvier—the tiny gaps where electrical signals jump from one section of a nerve fiber to the next. These widened gaps slowed down the signals and made them more erratic. The mice also performed worse on tests of motor coordination.
The team traced the problem to a protein called neurofascin 186, which helps organize the nodes of Ranvier. The MGAT5B enzyme adds branched sugar structures to this protein, and those sugar branches fine-tune how neurofascin interacts with another protein involved in organizing the node. By keeping these molecular interactions balanced, the sugar branches help preserve the narrow architecture needed for fast, reliable nerve transmission.
"Branching of glycans is critically involved in the formation of nodes of Ranvier, which in turn is required for fast and less variable nerve conduction," Kizuka said.
Perhaps most encouraging, the researchers found that restoring MGAT5B specifically in neurons corrected the node defects in the mice—showing that the enzyme acts directly within nerve cells to maintain proper structure.
The discovery opens new questions about brain diseases. The team now hopes to investigate whether problems with these sugar modifications might contribute to disorders involving myelin damage or impaired nerve conduction, such as multiple sclerosis.
For now, the findings offer a new piece of the puzzle about how the brain works—and a reminder that sometimes the smallest molecules, even sugars, play outsized roles in keeping us healthy.