Thursday, April 2, 2009, Condensed Matter Biological Physics Seminar, Jeffrey L. Brodsky, Department of Biological Sciences, University of Pittsburgh, "Doing the 'Impossible': Stripping Proteins from Biological Membranes", 4:30 PM, Doherty Hall A310, CMU
 

Abstract:

A large number of proteins that play critical roles in cellular physiology transit through the secretory pathway in order to reach their final sites of action. Although most secreted proteins fold efficiently, a significant percentage achieves the folded and thus active conformations with low efficiency.  Because unfolded protein accumulation can result in defects in cellular function and in some cases apoptosis, it is critical that aberrant proteins in the secretory pathway are recognized and are then selectively destroyed. 

 Secreted protein “quality control” occurs in the endoplasmic reticulum (ER), and we termed this process ER associated degradation (ERAD).  During ERAD, defective polypeptides are delivered from the ER, are ubiquitinated at the ER membrane, and are destroyed by the cytoplasmic proteasome.  Even though the identity of the ERAD channel remains mysterious, one can imagine that soluble proteins are simply recognized by ER molecular chaperones and are then re-inserted into this “retro-translocation” channel before they are targeted to the proteasome.  What has been more difficult to discern is how polytopic, integral membrane proteins are recognized and delivered to the proteasome while they are embedded within the ER membrane.

Using a novel in vitro system that employed components prepared from the yeast, S. cerevisiae, we found—surprisingly—that an integral membrane protein resided in solution prior to its degradation.  Moreover, membrane extraction required an ATP-utilizing enzyme complex, known as Cdc48/p97.  Current efforts are being directed to better define the energetic requirements for membrane protein extraction from the ER.