| Function | Small GTPase that cycles between an active GTP-bound and an inactive GDP-bound state and mainly functions in vesicle-mediated endoplasmic reticulum (ER) to Golgi transport. The active GTP-bound form inserts into the endoplasmic reticulum membrane where it recruits the remainder of the coat protein complex II/COPII. The coat protein complex II assembling and polymerizing on endoplasmic reticulum membrane is responsible for both the sorting of cargos and the deformation and budding of membranes into vesicles destined to the Golgi. In contrast to SAR1A, SAR1B specifically interacts with the cargo receptor SURF4 to mediate the transport of lipid-carrying lipoproteins including APOB and APOA1 from the endoplasmic reticulum to the Golgi and thereby, indirectly regulates lipid homeostasis. In addition to its role in vesicle trafficking, can also function as a leucine sensor regulating TORC1 signaling and more indirectly cellular metabolism, growth and survival. In absence of leucine, interacts with the GATOR2 complex via MIOS and inhibits TORC1 signaling. The binding of leucine abrogates the interaction with GATOR2 and the inhibition of the TORC1 signaling. This function is completely independent of the GTPase activity of SAR1B. |
| Protein Name | Small Copii Coat Gtpase Sar1bGtp-Binding Protein BGtbpbSecretion-Associated Ras-Related Gtpase 1b |
| Database Links | Reactome: R-HSA-1655829Reactome: R-HSA-204005Reactome: R-HSA-2132295Reactome: R-HSA-5694530Reactome: R-HSA-8963888Reactome: R-HSA-9705671Reactome: R-HSA-983170 |
| Cellular Localisation | Endoplasmic Reticulum MembranePeripheral Membrane ProteinGolgi ApparatusGolgi Stack MembraneCytoplasmCytosolLysosome MembraneActive At Endoplasmic Reticulum Exit Sites (Eres) Where It Inserts Into The Membrane And Recruits The Remainder Of The Coat Protein Complex Ii/CopiiUpon Leucine DeprivationAssociates With Lysosomal Membranes To Repress Torc1 Signaling |
| Alternative Protein Names | Small Copii Coat Gtpase Sar1b proteinGtp-Binding Protein B proteinGtbpb proteinSecretion-Associated Ras-Related Gtpase 1b proteinSAR1B proteinSARA2 proteinSARB protein |
Information sourced from Uniprot.org
