Transmembrane domain length determines intracellular membrane compartment localization of syntaxins 3, 4, and 5

Insulin recruits glucose transporter 4 (GLUT-4) vesicles from intracellular stores to the plasma membrane in muscle and adipose tissue by specific int eractions between the vesicle membrane-soluble N-ethylmaleimide-sensitive f actor attachment protein target receptor (SNARE) protein VAMP-2 and the tar get membrane SNARE protein syntaxin 4. Although GLUT-4 vesicle trafficking has been intensely studied, few have focused on the mechanism by which the SNAREs themselves localize to specific membrane compartments. We therefore set out to identify the molecular determinants for localizing several synta xin isoforms, including syntaxins 3, 4, and 5, to their respective intracel lular compartments (plasma membrane for syntaxins 3 and 4; cis-Golgi for sy ntaxin 5). Analysis of a series of deletion and chimeric syntaxin construct s revealed that the 17-amino acid transmembrane domain of syntaxin 5 was su fficient to direct the cis-Golgi localization of several heterologous repor ter constructs. In contrast, the longer 25-amino acid transmembrane domain of syntaxin 3 was sufficient to localize reporter constructs to the plasma membrane. Furthermore, truncation of the syntaxin 3 transmembrane domain to 17 amino acids resulted in a complete conversion to cis-Golgi compartmenta lization that was indistinguishable from syntaxin 5. These data support a m odel wherein short transmembrane domains (less than or equal to 17 amino ac ids) direct the cis-Golgi localization of syntaxins, whereas long transmemb rane domains (greater than or equal to 23 amino acids) direct plasma membra ne localization.