Dynamin molecule needs constant company of GTP to form new vesicles, according to method detailed in Cell.
Researchers at The Scripps Research Institute have discovered how a cell actually performs the function of fission. The team created a system that allows them to watch cell membranes bud and then pinch off smaller vesicles in real time under a light microscope.
The prevailing theory that the molecule dynamin alone creates endocytosis by first forming long hairy spiral chains around the neck of a vesicle and then tightening it was proven incorrect, according to the Scripps team. Close analysis demonstrated that only in the continuous presence of Guanosine-5′-triphosphate (GTP), a purine nucleotide that acts as a fuel, does dynamin form short collars at the neck of the vesicles that then tighten to break them free of the membrane.
“Doing this without leaking is quite a feat,” says Sandra Schmid, Ph.D., chair of the Scripps Research Department of Cell Biology. “A cell’s outside environment is very nasty, and if any of that toxic fluid got into the cell, it would kill it.”
Investigators used tiny glass beads—200 of them could fit on to the head of a pin—and formed membranes around each one of them. Every bead contained a loosely fitting bi-layer membrane, just like a cell would have.
The scientists then added dynamin alone and watched what occurred. The beads formed long hairy spirals, just as the prevailing hypothesis would predict, but surprisingly no fission took place even when they added GTP later.
The researchers then tried a slightly different condition. They added GTP first and then dynamin to the membrane beads. In this case the team didn’t see any hairy structures whatsoever, just little vesicles popping off the beads – exactly what happens in cellular fission.
The article appears in the December 11 online issue of the Cell.