Journal of Biological Chemistry
Volume 277, Issue 48, 29 November 2002, Pages 46504-46511
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MEMBRANE TRANSPORT STRUCTURE FUNCTION AND BIOGENESIS
Oligomeric State and Stoichiometry of p24 Proteins in the Early Secretory Pathway*

https://doi.org/10.1074/jbc.M206989200Get rights and content
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The p24 proteins belong to a highly conserved family of membrane proteins that cycle in the early secretory pathway. They bind to the coat proteins of COPI and COPII vesicles, and are proposed to be involved in vesicle biogenesis, cargo uptake, and quality control, but their precise function is still under debate. Most p24 proteins form hetero-oligomers, essential for their correct localization and stability. Functional insights regarding the mechanisms of their steady state localization and the role of interaction with coat proteins has been hampered by a lack of data on their concentration and state of oligomerization within the endoplasmic reticulum, the intermediate compartment, and Golgi complex. We have determined for all mammalian p24 family members the size of the oligomers formed and their stoichiometric relation in each of these individual organelles. In contrast to earlier reports, we show that individual members exist as dimers and monomers and that the ratio between these two forms depends on both the organelle investigated and the p24 protein. We find unequal quantities, with p23 and p27 building up concentration gradients, ruling out a simple 1:1 stoichiometry. In addition, we show differential cycling of individual p24 members. These data point to a complex and dynamic system of altering dimerizations of the family members.

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*

Work in the laboratory of the authors is supported by grants of the German Research Foundation (to B. B. and F. T. W.), the Human Frontiers Science Program Organization (to F. T. W.), and the Peter and Traudl Engelhorn Foundation (to B. B.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org ) contains Figures I–V and their legends.