Oligomerization of a membrane protein correlates with its retention in the Golgi complex

There are two general ways to envision the specific retention of a protein by information contained within its transmembrane domain (for review see Machamer, 1991) . The first involves the recognition of this domain by a specific receptor that either blocks further movement in the exocytic pathway or retrieves escaped proteins back to the appropriate compartment. A receptor-based model also requires a mechanism for retention or recycling of the receptor itself. The second mechanism invokes changes in the tertiary or quaternary structure of the protein that are induced via the membrane-spanning domain when the protein encounters a particular microenvironment. Changes in protein structure could include oligomerization or aggregation (covalent or non-covalent) with other proteins or lipids, which would prevent movement of the protein into transport vesicles. The cis-Golgi may differ from the ER in lipid composition and divalent cation concentration. These changes in microenvironment could conceivably trigger a conformational shift in Golgi resident proteins upon their arrival in the appropriate compartment.