UniProt:Q9Y6B6 SAR1B

chain
  • chain:1-198
checksum 3F567683D7F509E6
comment
  • 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 (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).CATALYTIC ACTIVITY GTP + H2O = GDP + phosphate + H(+)ACTIVITY REGULATION Small GTPases activation is mediated by guanine exchange factors (GEF), while inactivation through hydrolysis of the bound GTP is stimulated by GTPase activating proteins (GAP) (By similarity). Activated by the guanine nucleotide exchange factor PREB/SEC12 that facilitates the loading of SAR1B with GTP (PubMed:32358066). GTP hydrolysis is stimulated by SEC23/24 (By similarity).BIOPHYSICOCHEMICAL PROPERTIES Homodimer; upon association with membrane (PubMed:32358066). Part of the coat protein complex II/COPII, composed of SEC23/24 and SEC13/31 heterodimers, that it helps recruit and assemble on endoplasmic reticulum (ER) membranes at ER exit site (PubMed:32358066). Interacts with PREB; PREB acts as a guanine nucleotide exchange factor facilitating the activation of SAR1B by loading it with GTP (PubMed:32358066). Interacts with SURF4; recruits the cargo receptor SURF4 and its lipoprotein cargos to COPII-coated ER to Golgi transport vesicles (PubMed:33186557). Interacts with MIOS; the interaction is direct, disrupted by the binding of leucine and mediates the interaction of SAR1B with the GATOR2 complex to negatively regulate the TORC1 signaling upon leucine deprivation (PubMed:34290409).SUBCELLULAR LOCATION Active at endoplasmic reticulum exit sites (ERES) where it inserts into the membrane and recruits the remainder of the coat protein complex II/COPII (PubMed:23433038). Upon leucine deprivation, associates with lysosomal membranes to repress TORC1 signaling (PubMed:34290409).TISSUE SPECIFICITY Expressed in many tissues including small intestine, liver, muscle and brain.DISEASE The disease is caused by variants affecting the gene represented in this entry.SIMILARITY Belongs to the small GTPase superfamily. SAR1 family.
crossReference
databaseName UniProt
dbId 64138
description
  • recommendedName: fullName evidence="14"Small COPII coat GTPase SAR1B ecNumber evidence="6 9"3.6.5.2 alternativeName: fullName evidence="12"GTP-binding protein B shortName evidence="12"GTBPB alternativeName: fullName evidence="16"Secretion-associated Ras-related GTPase 1B
displayName UniProt:Q9Y6B6 SAR1B
geneName
  • SAR1B
  • SARA2
  • SARB
identifier Q9Y6B6
isSequenceChanged false
keyword
  • 3D-structure
  • Cytoplasm
  • Disease variant
  • Endoplasmic reticulum
  • ER-Golgi transport
  • Golgi apparatus
  • GTP-binding
  • Hydrolase
  • Lysosome
  • Magnesium
  • Membrane
  • Metal-binding
  • Nucleotide-binding
  • Phosphoprotein
  • Protein transport
  • Proteomics identification
  • Reference proteome
  • Transport
modified [InstanceEdit:9983091] Weiser, Joel, 2026-02-20
moleculeType Protein
name
  • SAR1B
otherIdentifier
  • 11725341_a_at
  • 11741124_a_at
  • 11755347_x_at
  • 1554482_PM_a_at
  • 1554482_a_at
  • 17000079
  • 218254_PM_s_at
  • 218254_s_at
  • 223512_PM_at
  • 223512_at
  • 226742_PM_at
  • 226742_at
  • 230397_PM_at
  • 230397_at
  • 2876118
  • 2876119
  • 2876258
  • 2876259
  • 2876260
  • 2876261
  • 2876262
  • 2876264
  • 2876266
  • 2876267
  • 2876268
  • 2876269
  • 2876270
  • 2876271
  • 2876272
  • 2876273
  • 51128
  • 51694_at
  • 55439_at
  • 56030_at
  • 56323_at
  • 65565_at
  • 8114193
  • 82968_at
  • A_23_P92842
  • A_24_P916845
  • GE528291
  • GE79826
  • GO:0000166
  • GO:0002376
  • GO:0002474
  • GO:0003400
  • GO:0003924
  • GO:0003925
  • GO:0005515
  • GO:0005525
  • GO:0005737
  • GO:0005764
  • GO:0005765
  • GO:0005783
  • GO:0005789
  • GO:0005794
  • GO:0005829
  • GO:0006886
  • GO:0006888
  • GO:0012507
  • GO:0015031
  • GO:0016020
  • GO:0016050
  • GO:0016192
  • GO:0016787
  • GO:0030127
  • GO:0032368
  • GO:0032580
  • GO:0042953
  • GO:0046872
  • GO:0048208
  • GO:0055088
  • GO:0061024
  • GO:0065003
  • GO:0070971
  • GO:0090110
  • GO:0098772
  • GO:0140299
  • GO:0140353
  • GO:0140785
  • GO:1903432
  • GO:1904262
  • GO:1990253
  • HMNXSV003020664
  • Hs.19218.0.A1_3p_at
  • Hs.22883.0.A1_3p_at
  • Hs.279582.1.S2_3p_at
  • Hs2.279582.2.S1_3p_s_at
  • ILMN_1736888
  • ILMN_2287168
  • ILMN_2394296
  • PH_hs_0001691
  • PH_hs_0029595
  • TC05001793.hg
  • g7705826_3p_a_at
physicalEntity
referenceDatabase [ReferenceDatabase:2] UniProt
referenceGene
referenceTranscript
schemaClass ReferenceGeneProduct
secondaryIdentifier
  • SAR1B_HUMAN
  • D3DQA4
  • Q567T4
sequenceLength 198
species [Species:48887] Homo sapiens
stId uniprot:Q9Y6B6
url http://purl.uniprot.org/uniprot/Q9Y6B6
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