An intricate new three-dimensional protein
By visualizing how three neural proteins interact with one another, researchers have revealed how they help groups of brain cells release chemical messages at the same time.
The work describes a surprising new cooperation among the three proteins, and could offer insight into other processes where cells secrete molecules, including insulin and airway mucus. Howard Hughes Medical Institute (HHMI) Investigator Axel Brunger and colleagues report the results August 24 in the journal Nature.
When a group of neurons receives an electrical signal, the cells release chemicals called neurotransmitters nearly instantaneously – within less than one thousandth of a second. Neurons hold neurotransmitters in bubble-like structures called synaptic vesicles. These structures rest inside the end of long, thin projections that point toward neighboring cells. To free neurotransmitters from their bubbles, neurons must fuse vesicle membranes with the outer membrane of the projections. This opens the bubbles and dumps their contents into the space between cells. The chemical signals then float to neighboring cells to relay a message.
Scientists knew that three proteins are involved in spitting out neurons' chemical signals. A group of proteins called SNAREs provides energy for membrane fusion. Another protein, called synaptotagmin, releases neurotransmitters when calcium ions appear following an electrical signal. A third protein, complexin, prevents cells from spontaneously releasing neurotransmitters. Synaptotagmin and complexin each partner with SNARE proteins, but until now, scientists could not explain how these three components worked together.
