Multisubunit assembly of an integral plasma membrane channel protein, gap junction connexin43, occurs after exit from the ER.
Connexin43 (Cx43) is an integral plasma membrane protein that forms gap junctions between vertebrate cells. We have used sucrose gradient fractionation and chemical cross-linking to study the first step in gap junction assembly, oligomerization of Cx43 monomers into connexon channels. In contrast with other plasma membrane proteins, multisubunit assembly of Cx43 was specifically and completely blocked when endoplasmic reticulum (ER)-to-Golgi transport was inhibited by 15 degrees C incubation, carbonyl cyanide m-chloro-phenylhydrazone, or brefeldin A or in CHO cell mutants with temperature-sensitive defects in secretion. Additional experiments indicated that connexon assembly occurred intracellularly, most likely in the trans-Golgi network. These results describe a post-ER assembly pathway for integral membrane proteins and have implications for the relationship between membrane protein oligomerization and intracellular transport.
Musil
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LS
Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115.
Goodenough
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DA
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D020126:Brefeldin A; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D018031:Connexin 43 / Q000096:biosynthesis* / Q000302:isolation & purification; D003517:Cyclopentanes / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism*; D007668:Kidney; D046911:Macromolecular Substances; D008715:Methionine / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012313:RNA / Q000378:metabolism; D051381:Rats; D013462:Sulfur Radioisotopes; D014981:Xenopus
D000900:Anti-Bacterial Agents; D018031:Connexin 43; D003517:Cyclopentanes; D046911:Macromolecular Substances; D013462:Sulfur Radioisotopes; D020126:Brefeldin A; D012313:RNA; D008715:Methionine