"TA proteins play all sort of important roles in a variety of different cellular functions," Keenan said. "If you screw this pathway up, bad things will happen. At that level they are just fundamentally important."
The first component from this new system was identified in 2007 by Hegde (now at the MRC Laboratory of Molecular biology in Cambridge, England). That protein, called Get3 in yeast, was subsequently discovered to interact with two proteins called Get1 and Get2. But researchers hadn't yet determined how these components worked, and whether these three alone could account for TA protein targeting.
Leading the collaboration between Keenan and Hegde's laboratories, co-first authors Agnieszka Mateja of the University of Chicago and Malaiyalam Mariappan of the National Institute of Child Health and Human Development created a synthetic system containing only Get1, Get2, Get3, and a TA protein substrate. The substrate was successfully delivered to the endoplasmic reticulum membrane, confirming that the three-part system was sufficient for trafficking.
The scientists then deleted or modified specific pieces of the Get proteins to see how these elements work together to move a tail-anchored protein to its proper position in the cell membrane. The new model of the pathway includes both Dr. Octopus-like hooks, a handoff between two closely partnered proteins, and an elegant system for recycling.
1. A complex of two Get3's bound to two molecules of ATP form a "groove" of the right size and chemical properties to capture a tail-anchored protein (the "substrate") in the cytosol.
2. Once the substrate is safely nestled in the groove, "hooks" on the end of Get2 grab the complex, and bring it to the membrane. The long, flexible arms of Get2 allow it to function in a way that Keenan jokingly
|Contact: Robert Mitchum|
University of Chicago Medical Center