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  current news   Press   selected story    
     
  25th August 2010  
 

p125A exists as part of the mammalian Sec13/Sec31 COPII subcomplex to facilitate ER-Golgi transport

 
 




Authors: Ong YS, Tang BL, Loo LS, Hong W.

Cancer and Developmental Cell Biology Division, IMCB, Proteos, Singapore 138673.

Published in Journal of Cell Biology, 2010 Aug 2. [Epub ahead of print]

Abstract
Coat protein II (COPII)-mediated export from the endoplasmic reticulum (ER) involves sequential recruitment of COPII complex components, including the Sar1 GTPase, the Sec23/Sec24 subcomplex, and the Sec13/Sec31 subcomplex. p125A was originally identified as a Sec23A-interacting protein. Here we demonstrate that p125A also interacts with the C-terminal region of Sec31A. The Sec31A-interacting domain of p125A is between residues 260-600, and is therefore a distinct domain from that required for interaction with Sec23A. Gel filtration and immunodepletion studies suggest that the majority of cytosolic p125A exists as a ternary complex with the Sec13/Sec31A subcomplex, suggesting that Sec 13, Sec31A, and p125A exist in the cytosol primarily as preassembled Sec13/Sec31A/p125A heterohexamers. Golgi morphology and protein export from the ER were affected in p125A-silenced cells. Our results suggest that p125A is part of the Sec13/Sec31A subcomplex and facilitates ER export in mammalian cells.

 
 


 
 


Figure Legend: p125A stabilizes the Sec13/Sec31 heterotetramer to the ERES membrane.
A, Membrane (m) and cytosol (c) fractions were obtained from cells transfected with siRNA. Equivalent amounts of each fraction were analyzed by immunoblot analysis. The intensities of the bands were quantified using Quantity One software (Biorad). The ratio of distribution is relative to the total. Total = m (membrane fraction) + c (cytosol fraction). Ratio = m or c/(m+c). The experiment was repeated three times, *P<0.05. Syn6 and RhoGDI were used as control for the membrane and cytosol fraction, respectively.   BA working model to illustrate the role of p125A in ER export in mammalian cells. The majority of p125A, Sec31A and Sec13 exists likely in the form of a heterohexamer. Upon recruitments of Sar1 and Sec23A/Sec24 subcomplex during COPII vesicle budding, the p125A-Sec31A-Sec13 subcomplex is then recruited, which may open up the binding site of p125A for Sec23A. The simultaneous interaction of p125A with both Sec31A and Sec23A on the budding vesicles may facilitate the coordination of these two COPII subcomplexes to mediate vesicle formation.

For more information on Wanjin HONG's Lab, please click here.