"It's unusual in that it actually contains not one but two distinct enzymes -- each of which clips off phosphate at a different position or domain on the lipid molecule, in this case the '4' and '5' positions," explained lead researcher Meera Mani, an M.D/Ph.D. candidate in Dr. Ryan's lab.
In prior research, researchers led by Dr. Pietro de Camilli, of Yale University School of Medicine and the Howard Hughes Medical Institute, found that synj1 was essential to vesicle recycling. Their work showed that synj1 helped strip vesicles of a clathrin molecule "coat" once it had delivered its cargo to the cell membrane.
Collaborating on the new study, Dr. Ryan and Dr. de Camilli wanted to see if synj1 played an even greater role in the life of the synapse.
"We found that it does," Dr. Ryan says. In fact, endocytosis slows down once synj1 is disabled in any key way, he says.
In their experiments, Drs. Ryan and de Camilli created genetically engineered "knockouts" of the dual-enzyme synj1 to which they could then add back different versions of the protein. One version lacked the functioning enzyme aimed at the 4 position, while another lacked the functioning enzyme aimed at the 5 position. "We also created a third variant that mutated the 'tail' of the synj1 molecule, rendering it unable to 'talk to' certain elements of the endocytic machinery," Dr. Ryan says.
In each case, endocytosis slowed to a crawl, due in part, at least, to a buildup of clathrin coating on vesicles.
Some synj1 mutations were more disruptive than others. "Dysfunction in the dephosphorylating enzyme for position 5 was universally disruptive, but the other two mutants were pretty effective at putting a stop to endocytosis, too," Mani notes.
On the other hand, simply adding normal s
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New York- Presbyterian Hospital/Weill Cornell Medical Center/Weill Cornell Medical College