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[https://www.uniprot.org/uniprot/SAR1B_HUMAN SAR1B_HUMAN] Chylomicron retention disease. The disease is caused by variants affecting the gene represented in this entry.

== Function ==

[https://www.uniprot.org/uniprot/SAR1B_HUMAN SAR1B_HUMAN] GTP-~~binding protein involved~~ in transport ~~from~~ the endoplasmic reticulum to the ~~Golgi apparatus (By similarity). Activated by~~ the ~~guanine nucleotide exchange factor PREB~~ (~~By similarity~~). ~~Involved in~~ the ~~selection~~ of the ~~protein cargo~~ and ~~the assembly~~ of the ~~COPII coat complex~~ (~~By similarity~~). ~~Synergizes~~ with the cargo receptor SURF4 to mediate the ~~export~~ of lipoproteins from the endoplasmic reticulum, ~~thereby~~ regulating ~~lipoprotein delivery~~ and the ~~maintenance~~ of ~~lipid homeostasis~~ (PubMed:~~33186557~~).~~[UniProtKB~~:~~Q9QVY3]~~<ref>PMID:33186557</ref>

[https://www.uniprot.org/uniprot/SAR1B_HUMAN SAR1B_HUMAN] 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 (PubMed:23433038, PubMed:32358066, PubMed:33186557, PubMed:36369712). 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 (PubMed:23433038, PubMed:32358066, PubMed:33186557). 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 (PubMed:32358066, PubMed:33186557). 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 (PubMed:34290409).<ref>PMID:23433038</ref> <ref>PMID:32358066</ref> <ref>PMID:33186557</ref> <ref>PMID:34290409</ref> <ref>PMID:36369712</ref>

== References ==

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 [https://www.uniprot.org/uniprot/SAR1B_HUMAN SAR1B_HUMAN] Chylomicron retention disease. The disease is caused by variants affecting the gene represented in this entry.
 == Function ==
-[https://www.uniprot.org/uniprot/SAR1B_HUMAN SAR1B_HUMAN] GTP-binding protein involved in transport from the endoplasmic reticulum to the Golgi apparatus (By similarity). Activated by the guanine nucleotide exchange factor PREB (By similarity). Involved in the selection of the protein cargo and the assembly of the COPII coat complex (By similarity). Synergizes with the cargo receptor SURF4 to mediate the export of lipoproteins from the endoplasmic reticulum, thereby regulating lipoprotein delivery and the maintenance of lipid homeostasis (PubMed:33186557).[UniProtKB:Q9QVY3]<ref>PMID:33186557</ref>
+[https://www.uniprot.org/uniprot/SAR1B_HUMAN SAR1B_HUMAN] 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 (PubMed:23433038, PubMed:32358066, PubMed:33186557, PubMed:36369712). 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 (PubMed:23433038, PubMed:32358066, PubMed:33186557). 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 (PubMed:32358066, PubMed:33186557). 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 (PubMed:34290409).<ref>PMID:23433038</ref> <ref>PMID:32358066</ref> <ref>PMID:33186557</ref> <ref>PMID:34290409</ref> <ref>PMID:36369712</ref>
 == References ==
 <references/>