Affinage

RAB33B

Ras-related protein Rab-33B · UniProt Q9H082

Length
229 aa
Mass
25.7 kDa
Annotated
2026-04-28
24 papers in source corpus 16 papers cited in narrative 16 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

RAB33B is a medial-Golgi-resident small GTPase that functions as a regulatory hub linking intra-Golgi retrograde trafficking with autophagosome biogenesis. In its GTP-bound form, RAB33B recruits the Ric1–Rgp1 Rab6 GEF complex to medial-Golgi membranes, establishing a Rab cascade that drives retrograde transport from trans- to cis-Golgi and ER, and also interacts with GM130 and the exocyst subunit Exoc6 to regulate Golgi integrity and integrin delivery to focal adhesions (PMID:20163571, PMID:23091056, PMID:11718716, PMID:35521520). Upon starvation, RAB33B translocates from the Golgi to phagophores via an LIR motif that binds GATE16, where it directly engages the ATG16L1 coiled-coil domain—acting as a noncanonical Rab-binding protein that stabilizes the active RAB33B conformation—to recruit the ATG12–ATG5–ATG16L1 complex for LC3 lipidation and autophagosome formation (PMID:32960676, PMID:18448665, PMID:40855209). Loss-of-function mutations in RAB33B cause Smith–McCort dysplasia through protein instability, Golgi mislocalization, and impaired autophagy (PMID:41506134).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 1998 High

    Establishing that RAB33B is a novel Rab GTPase resident on medial-Golgi cisternae answered the fundamental question of where this GTPase acts and implicated it in intra-Golgi transport.

    Evidence Co-localization with alpha-mannosidase II by immunofluorescence and immunoelectron microscopy in mammalian cells

    PMID:9512502

    Open questions at the time
    • No effectors or transport cargo identified
    • No functional loss-of-function data
  2. 2001 High

    Identifying GM130, rabaptin-5, and rabex-5 as GTP-dependent interactors and showing that constitutively active RAB33B blocks anterograde Golgi transport and glycosyltransferase recycling established that RAB33B regulates vesicular trafficking within the Golgi.

    Evidence GST pulldown with GTP-locked RAB33B, mass spectrometry identification, microinjection of GTPase mutants in mammalian cells

    PMID:11718716

    Open questions at the time
    • Endogenous loss-of-function phenotype not tested
    • Direct versus indirect binding to GM130 not resolved
  3. 2008 High

    Discovery of the GTP-dependent RAB33B–ATG16L1 interaction and its ability to induce LC3 lipidation revealed an unexpected autophagy function for a Golgi Rab, linking Golgi membranes to autophagosome biogenesis.

    Evidence Co-immunoprecipitation, GTPase-deficient Q92L mutant expression, LC3 lipidation and p62 degradation assays in cultured cells

    PMID:18448665

    Open questions at the time
    • Structural basis of RAB33B–ATG16L1 recognition unknown
    • Mechanism of RAB33B translocation to phagophores unclear
  4. 2010 High

    Demonstrating that RAB33B operates downstream of Rab6 and is required for Shiga toxin retrograde transport established a Rab cascade governing intra-Golgi retrograde trafficking.

    Evidence siRNA knockdown, GTP-locked mutant overexpression, Shiga toxin transport assay, Golgi ribbon disruption in mammalian cells

    PMID:20163571

    Open questions at the time
    • The GEF connecting Rab6 activity to RAB33B activation was not identified
    • No reconstitution of the cascade in vitro
  5. 2011 High

    Identification of OATL1 and RUTBC1 as GAPs for RAB33B defined the inactivation machinery and placed RAB33B cycling in the context of autophagosome maturation (OATL1) and Rab9A effector function (RUTBC1).

    Evidence In vitro GTP hydrolysis assays with catalytic residue mutagenesis, co-immunoprecipitation, autophagosome–lysosome fusion readout

    PMID:21383079 PMID:21808068

    Open questions at the time
    • Whether OATL1 and RUTBC1 act on RAB33B at distinct subcellular sites in vivo not resolved
    • Relative contributions of different GAPs to RAB33B steady-state activity unknown
  6. 2012 High

    Demonstrating that the Ric1–Rgp1 complex is both an effector of RAB33B-GTP and a GEF for Rab6A provided the molecular mechanism linking the medial-Golgi RAB33B pool to trans-Golgi Rab6 activation.

    Evidence In vitro nucleotide exchange assay, RAB33B-GTP binding to Ric1 C-terminus, loss-of-function phenocopying Rab6 destabilization

    PMID:23091056

    Open questions at the time
    • Structural basis of Ric1–RAB33B interaction not determined
    • Whether additional GEFs exist for RAB33B itself remains unknown
  7. 2017 Medium

    Identification of ACBD3 as a scaffold recruiting the RAB33B-GAP TBC1D22 together with Golgin45 and GRASP55 revealed a multiprotein complex that couples RAB33B inactivation to Golgi stacking.

    Evidence Proteomics, co-immunoprecipitation, co-expression targeting assay in mammalian cells

    PMID:28777890

    Open questions at the time
    • Functional consequence of TBC1D22 loss on RAB33B-GTP levels not quantified
    • No reconstitution of the quaternary complex in vitro
    • Single-lab observation
  8. 2020 High

    Crystal structures of RAB33B bound to the ATG16L1 coiled-coil domain resolved the molecular recognition mechanism and showed that ATG16L1 acts as a noncanonical Rab-binding protein stabilizing active RAB33B without nucleotide exchange, directly explaining how RAB33B recruits autophagy machinery to phagophores.

    Evidence X-ray crystallography, microscale thermophoresis, FLIM-FRET, mutagenesis, LC3 lipidation assay, correlative light-electron microscopy

    PMID:32960676

    Open questions at the time
    • How RAB33B is activated (GEF identity) before encountering ATG16L1 remains unknown
    • Stoichiometry of the complex on native phagophore membranes not determined
  9. 2022 Medium

    Discovery of the RAB33B–Exoc6 interaction and its role in integrin delivery to focal adhesions extended RAB33B function from Golgi/autophagy to post-Golgi secretory trafficking and cell migration.

    Evidence siRNA migration screen, co-immunoprecipitation, focal adhesion turnover and integrin trafficking assays, live imaging

    PMID:35521520

    Open questions at the time
    • Whether Exoc6 binding competes with ATG16L1 binding unknown
    • Mechanism of cargo selectivity for integrin not addressed
    • Single-lab study
  10. 2025 Medium

    Identification of an LIR motif in RAB33B that specifically binds GATE16 (not LC3B) defined the molecular mechanism for starvation-induced Golgi-to-phagophore translocation, while disease-causing RAB33B mutations were shown to cause protein instability, Golgi mislocalization, and impaired autophagy, explaining Smith–McCort dysplasia pathogenesis.

    Evidence LIR motif mutagenesis with live imaging, LC3B-puncta assays, ectopic expression of five disease variants with localization and stability readouts

    PMID:40855209 PMID:41506134

    Open questions at the time
    • GATE16 selectivity over other ATG8 paralogs not structurally explained
    • Disease variant effects tested only by overexpression, not in patient cells or knockin models
    • Single-lab studies for each finding

Open questions

Synthesis pass · forward-looking unresolved questions
  • The GEF that activates RAB33B at the Golgi remains unidentified, and how RAB33B partitions between its Golgi trafficking, autophagy, and exocyst-mediated secretory roles is mechanistically unresolved.
  • No RAB33B GEF identified
  • Regulatory logic for switching between Golgi-resident and phagophore-targeted pools unknown
  • No animal model with conditional Rab33b loss to separate trafficking versus autophagy phenotypes

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003924 GTPase activity 4
Localization
GO:0005794 Golgi apparatus 5 GO:0005829 cytosol 2
Pathway
R-HSA-9612973 Autophagy 5 R-HSA-5653656 Vesicle-mediated transport 4 R-HSA-1643685 Disease 1
Partners
ATG16L1EXOC6GATE16GOLGA3OATL1RGP1RIC1TBC1D22A

Evidence

Reading pass · 16 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1998 RAB33B is a novel Rab GTPase that localizes to the medial Golgi cisternae, as demonstrated by co-localization with alpha-mannosidase II by immunofluorescence and immunoelectron microscopy, suggesting a role in intra-Golgi transport. Immunofluorescence, immunoelectron microscopy, Western blotting with Rab33B-specific monoclonal antibody Journal of cell science High 9512502
2001 RAB33B in its GTP-bound state interacts with Golgi protein GM130 and endocytic Rab effectors rabaptin-5 and rabex-5; microinjection of GTP-locked Rab33B mutants inhibited anterograde transport within the Golgi and recycling of glycosyltransferases from Golgi to ER. GST pulldown with GTP-locked Rab33B fusion protein, Western blotting/mass spectrometry for interactor identification, microinjection of GTPase mutants FEBS letters High 11718716
2008 RAB33B (and RAB33A) specifically interacts with Atg16L in a GTP-dependent manner; expression of GTPase-deficient RAB33B-Q92L induced LC3 lipidation under nutrient-rich conditions and attenuated macroautophagy, demonstrating that RAB33B modulates autophagosome formation through Atg16L interaction. Co-immunoprecipitation, GTP-dependent binding assay, overexpression of GTPase-deficient mutant (Q92L), LC3 lipidation assay, p62/SQSTM1 degradation assay Molecular biology of the cell High 18448665
2010 RAB33B acts downstream of trans-Golgi Rab6 in a Rab cascade regulating intra-Golgi retrograde trafficking; GTP-restricted Rab6-induced relocation of Golgi enzymes to the ER was RAB33B-dependent, overexpression of GTP-RAB33B displaced Rab6 from Golgi membranes, and RAB33B was required for Shiga-like toxin B fragment transport from trans to cis Golgi and ER. siRNA knockdown, overexpression of GTP-locked mutants, Golgi ribbon disruption assay, Shiga toxin transport assay, immunofluorescence Traffic (Copenhagen, Denmark) High 20163571
2011 OATL1, an autophagosome-resident Rab-GAP, is recruited to autophagosomes via direct interaction with Atg8 homologues, and RAB33B is a target substrate of OATL1; both OATL1 GAP activity and Atg8 homologue binding are required for autophagosome-lysosome fusion, placing RAB33B in the autophagosomal maturation pathway. Identification of Rab33B as OATL1 GAP substrate by in vitro GTP hydrolysis assay, co-immunoprecipitation, loss-of-function (GAP mutants, Atg8 interaction mutants) with autophagosome-lysosome fusion readout The Journal of cell biology High 21383079
2011 RUTBC1 (a TBC-domain Rab9A effector) activates GTP hydrolysis by RAB33B in vitro, requiring Arg-803 of RUTBC1 consistent with a dual-finger catalytic mechanism; however, RUTBC1 did not influence RAB33B–Atg16L1 interaction in cells. In vitro GTP hydrolysis assay, Arg-803 mutagenesis, co-immunoprecipitation in cells and cell extracts The Journal of biological chemistry High 21808068
2012 The Ric1–Rgp1 complex acts as a GEF for Rab6A and as an effector of RAB33B-GTP; the C terminus of Ric1 contains a distinct binding site for RAB33B-GTP, supporting a Rab cascade between medial (RAB33B) and trans (Rab6) Golgi compartments. In vitro nucleotide exchange assay (GEF activity reconstitution), binding assays for Rab33B-GTP interaction with Ric1 C-terminus, loss-of-function showing Rab6 destabilization and retrograde transport block The Journal of biological chemistry High 23091056
2015 RAB33B is required for hepatitis B virus naked capsid formation and release; RAB33B functions together with its effector Atg5-Atg12/Atg16L1 complex in this process, as silencing of either RAB33B or ATG5/ATG12/ATG16L1 impaired capsid egress and proper particle assembly/stability. RNA interference knockdown, overexpression studies, capsid assembly/release assays, co-localization by immunofluorescence Cellular microbiology Medium 25439980
2016 Atg5 is required for augmented nucleotide-dependent interaction of RAB33B with the Atg5-Atg16L1 dimeric complex; Arg-24 of Atg16L1 is critical for its interaction with Atg5, which in turn influences RAB33B binding to the complex. GST pulldown, isothermal titration calorimetry (ITC), mutational analysis of Atg16L1 Arg-24 Biochemical and biophysical research communications Medium 26975471
2017 ACBD3 recruits TBC1D22, a RAB33B GTPase-activating protein, to a multi-protein complex containing Golgin45 and GRASP55 at the medial Golgi, acting as a scaffold for Golgi stacking proteins and a Rab33B-GAP. Proteomics/co-immunoprecipitation, co-expression targeting assay FEBS letters Medium 28777890
2017 RAB33B is required for HBV propagation; it regulates nucleocapsid (NC) formation/trafficking and core membrane association through a membrane targeting module in the core protein C-terminal domain; GDP-restricted RAB33B phenocopied knockdown, and Rab33B inactivation reduced core membrane association and impaired core/NC sorting to envelope-positive compartments. RNAi knockdown, GDP-restricted mutant overexpression, immunofluorescence, Western blotting, viral replication assays Viruses Medium 28635671
2020 Crystal structures of RAB33B bound to the coiled-coil domain (CCD) of ATG16L1 revealed the molecular recognition mechanism; ATG16L1 acts as a noncanonical RAB-binding protein (RBP) that induces RAB33B to adopt an active conformation without nucleotide exchange; upon starvation, RAB33B translocates from the Golgi to phagophores and recruits the ATG12-ATG5-ATG16L1 complex, which is required for LC3 lipidation and autophagosome formation. X-ray crystallography, microscale thermophoresis (MST), FLIM-FRET, live imaging, mutagenesis, LC3 lipidation assay, correlative light and electron microscopy (CLEM) Autophagy High 32960676
2022 RAB33B interacts with Exoc6, a subunit of the exocyst complex, and mediates post-Golgi secretion to the plasma membrane; RAB33B regulates focal adhesion dynamics by controlling integrin delivery to focal adhesions, thereby promoting cell migration. siRNA screen for cell migration, Co-immunoprecipitation (RAB33B-Exoc6), focal adhesion turnover assay, integrin trafficking assay, live imaging iScience Medium 35521520
2025 RAB33B contains an LIR motif that specifically interacts with GATE16 (but not LC3B or other ATG8 homologs); upon autophagy induction, RAB33B is recruited from the Golgi to the phagophore in an LIR-dependent manner, interacts with TRPML3, and promotes autophagosome formation. Co-immunoprecipitation, LIR motif mutagenesis, live imaging of RAB33B translocation, autophagy assays with LC3B-puncta readout Scientific reports Medium 40855209
2025 Five disease-causing RAB33B mutants (two truncations, three missense) mislocalize from the Golgi, are unstable and prematurely degraded, and overexpression of the missense variants severely reduces autophagosome (LC3B-puncta) number upon autophagy induction, demonstrating that Golgi localization is required for RAB33B's autophagy function. Ectopic expression of RAB33B disease variants, immunofluorescence localization, Western blot stability assay, LC3B-puncta counting assay European journal of cell biology Medium 41506134
2025 RAB33B promotes influenza A virus (IAV) replication by enhancing autophagy and facilitates IAV M2 protein trafficking to the plasma membrane through autophagic-like vesicles; ATG16L1 (RAB33B effector) and TBC1D25 (RAB33B GAP) also contribute to this M2-induced autophagy. Transcriptomics, RAB33B overexpression/knockdown, autophagy assays, co-immunoprecipitation of M2-RAB33B-LC3, viral replication assays Veterinary research Medium 40598642

Source papers

Stage 0 corpus · 24 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2008 Golgi-resident small GTPase Rab33B interacts with Atg16L and modulates autophagosome formation. Molecular biology of the cell 228 18448665
2011 OATL1, a novel autophagosome-resident Rab33B-GAP, regulates autophagosomal maturation. The Journal of cell biology 137 21383079
2001 Identification of rabaptin-5, rabex-5, and GM130 as putative effectors of rab33b, a regulator of retrograde traffic between the Golgi apparatus and ER. FEBS letters 102 11718716
2010 Rab33b and Rab6 are functionally overlapping regulators of Golgi homeostasis and trafficking. Traffic (Copenhagen, Denmark) 71 20163571
1998 A novel Rab GTPase, Rab33B, is ubiquitously expressed and localized to the medial Golgi cisternae. Journal of cell science 65 9512502
2012 Ric1-Rgp1 complex is a guanine nucleotide exchange factor for the late Golgi Rab6A GTPase and an effector of the medial Golgi Rab33B GTPase. The Journal of biological chemistry 63 23091056
2011 RUTBC1 protein, a Rab9A effector that activates GTP hydrolysis by Rab32 and Rab33B proteins. The Journal of biological chemistry 52 21808068
2015 Rab33B and its autophagic Atg5/12/16L1 effector assist in hepatitis B virus naked capsid formation and release. Cellular microbiology 38 25439980
2019 Multitasking Rab Proteins in Autophagy and Membrane Trafficking: A Focus on Rab33b. International journal of molecular sciences 37 31408960
2012 Mutation in RAB33B, which encodes a regulator of retrograde Golgi transport, defines a second Dyggve--Melchior--Clausen locus. Journal of medical genetics 33 22652534
2020 RAB33B recruits the ATG16L1 complex to the phagophore via a noncanonical RAB binding protein. Autophagy 32 32960676
2012 A novel RAB33B mutation in Smith-McCort dysplasia. Human mutation 32 23042644
2016 A systematic High-Content Screening microscopy approach reveals key roles for Rab33b, OATL1 and Myo6 in nanoparticle trafficking in HeLa cells. Scientific reports 20 27374232
2017 ACBD3 functions as a scaffold to organize the Golgi stacking proteins and a Rab33b-GAP. FEBS letters 18 28777890
2017 Rab33B Controls Hepatitis B Virus Assembly by Regulating Core Membrane Association and Nucleocapsid Processing. Viruses 16 28635671
2017 Additional three patients with Smith-McCort dysplasia due to novel RAB33B mutations. American journal of medical genetics. Part A 15 28127940
2022 Rab33b-exocyst interaction mediates localized secretion for focal adhesion turnover and cell migration. iScience 7 35521520
2016 Deciphering the role of Atg5 in nucleotide dependent interaction of Rab33B with the dimeric complex, Atg5-Atg16L1. Biochemical and biophysical research communications 6 26975471
2010 Proteomic approach with LCMS-IT-TOF identified an increase of Rab33B after transient focal cerebral ischemia in mice. Experimental & translational stroke medicine 6 21092243
2021 RAB33B and PCNT variants in two Pakistani families with skeletal dysplasia and short stature. BMC musculoskeletal disorders 5 34284742
2023 A Rab33b missense mouse model for Smith-McCort dysplasia shows bone resorption defects and altered protein glycosylation. Frontiers in genetics 1 37359363
2025 Host cellular protein RAB33B facilitates influenza viral replication and modulates M2 trafficking by enhancing autophagy. Veterinary research 0 40598642
2025 Two specific interactions of GATE16 with TRPML3 and RAB33B regulate autophagy. Scientific reports 0 40855209
2025 Mutations in the Rab33b protein that lead to the skeletal disease Smith-McCort dysplasia result in unstable proteins and altered autophagy function. European journal of cell biology 0 41506134