This, in all its molecular complexity, is what the bulging end of a single neuron looks like. A whopping 300,000 proteins come together to form the structure, which is less than a micrometer wide, hundreds of times smaller than a grain of sand. This particular synapse is from a rat brain. It’s where chemical signals called neurotransmitters are released into the space between neurons to pass messages from cell to cell. To create a 3D molecular model of the structure, researchers first isolated the synapses of rat neurons and turned to classic biochemistry to identify and quantify the molecules present at every stage of the neurotransmitter release cycle. Then, they used microscopy to pinpoint the location of each protein. Some proteins—like the red patches of SNAP25 visible in the video at 0:14—aid in the release of vesicles, tiny spheres full of neurotransmitters. Others—like the green, purple, and red rods at 0:45—help the synapse maintain its overall structure. Different proteins surround vesicles when they’re inside the synapse—the circles scattered throughout the structure at 0:56—than when the vesicles are forming at the edge of the synapse—as shown at 2:08. Researchers can use the model, described online today in Science, to better understand how neurons function and what goes wrong in brain disorders.
(Video credit: Wilhelm et al. 2014, Science)