The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
MVB12B (Multivesicular body subunit 12B, also known as FAM125B, C9orf28) is a cytosolic protein in Homo sapiens and a structural component of the ESCRT-I (Endosomal Sorting Complex Required for Transport-I) complex (morita2007identificationofhuman pages 1-2, flower2020ahelicalassembly pages 1-2, morita2007identificationofhuman pages 3-5). As the fourth subunit within the core ESCRT-I heterotetramer (the others are TSG101, VPS28, VPS37), MVB12B fulfills an adaptor/scaffold role in recognizing and sorting ubiquitinated membrane proteins into intraluminal vesicles (ILVs) of multivesicular bodies (MVBs), a critical process for endosomal trafficking, lysosome targeting, and exosome secretion (vietri2020themanyfunctions pages 1-2, morita2007identificationofhuman pages 5-6, kuchitsu2023stingsignallingis pages 1-2).
MVB12B encompasses two key domains:
- MABP domain, implicated in membrane interactions and trafficking.
- UMA (UBAP1-MVB12-associated) domain, essential for ESCRT-I integration and cargo recognition (souza2010umaandmabp pages 1-2).
The protein is not an enzyme and does not possess substrate specificity in the classical sense; its molecular role is instead structural and regulatory within the ESCRT-I assembly (morita2007identificationofhuman pages 1-2, vietri2020themanyfunctions pages 1-2).
Recent reviews (2023–2024) of the ESCRT system confirm MVB12B’s importance in:
- Endosomal trafficking, MVB/exosome biogenesis, and reverse-topology membrane remodeling events such as virus budding, autophagosome closure, and cytokinesis (vietri2020themanyfunctions pages 1-2, vietri2020themanyfunctions pages 2-3, vietri2020themanyfunctions pages 3-4).
- Immune regulation: Landmark studies reveal that TBK1-dependent phosphorylation of MVB12B is a critical trigger for sorting cytosolic DNA into extracellular vesicles via ESCRT-I, enabling paracrine cGAS–STING signaling during bacterial infection (kuchitsu2023stingsignallingis pages 1-2, nandakumar2019intracellularbacteriaengage pages 1-5, nandakumar2019intracellularbacteriaengage pages 5-15).
- Viral egress: New structural biology work (Flower et al. 2020) details the helical organization of human ESCRT-I and the essential scaffolding role of MVB12B and relatives in membrane remodeling, especially at viral assembly sites (flower2020ahelicalassembly pages 1-2).
MVB12B is primarily cytosolic, becoming transiently and specifically recruited to endosomal and multivesicular body (MVB) membranes during ILV biogenesis. It localizes to early and late endosomes and MVBs, where it participates in complex assembly, cargo recognition, and vesicle scission (vietri2020themanyfunctions pages 1-2, morita2007identificationofhuman pages 1-2, morita2007identificationofhuman pages 3-5).
Within the ESCRT-I complex, MVB12B interacts with TSG101 and VPS37 (via conserved C-terminal elements), forming a 1:1:1:1 heterotetrameric assembly that binds upstream factors and mediates downstream ESCRT-II/III recruitment for membrane budding and scission (flower2020ahelicalassembly pages 1-2, flower2020ahelicalassembly pages 3-4, souza2010umaandmabp pages 1-2, morita2007identificationofhuman pages 5-6).
The following tables summarize, respectively, the protein features of MVB12B and its roles in key cellular pathways, with direct citation mapping:
| Feature | Summary | Evidence/Citation |
|---|---|---|
| Approved identity | Human MVB12B protein corresponding to UniProt Q9H7P6; also called FAM125B and C9orf28 | Primary literature identifies human MVB12B/FAM125B as an ESCRT-I subunit and distinguishes it from the related paralog MVB12A (morita2007identificationofhuman pages 1-2, morita2007identificationofhuman pages 3-5) |
| Protein family | Member of the MVB12 family, one of the metazoan fourth-subunit classes of ESCRT-I | Human ESCRT-I contains TSG101, VPS28, VPS37, and a fourth subunit such as MVB12A/MVB12B; UMA-containing proteins are the metazoan MVB12-type subunits (flower2020ahelicalassembly pages 1-2, vietri2020themanyfunctions pages 1-2, souza2010umaandmabp pages 1-2) |
| Main molecular role | Structural/adaptor subunit of ESCRT-I involved in endosomal cargo sorting and reverse-topology membrane remodeling rather than enzymatic catalysis | ESCRT-I is an upstream complex in multivesicular body biogenesis and other membrane scission events; MVB12 proteins constitute the fourth ESCRT-I subunit class (morita2007identificationofhuman pages 1-2, vietri2020themanyfunctions pages 1-2) |
| Core binding partners | Directly associates with TSG101 and VPS37 within the ESCRT-I core; assembled complex also includes VPS28 | Mapping experiments showed MVB12 proteins bind the TSG101–VPS37 binary complex, and quaternary complexes contain TSG101, VPS28, VPS37, and MVB12 (morita2007identificationofhuman pages 3-5, morita2007identificationofhuman pages 5-6) |
| Binding architecture | MVB12-family proteins incorporate into the ESCRT-I head/core through the UMA region; human MVB12A structure indicates analogous occupancy of the MVB12 site in human ESCRT-I | Structural work showed UMA-containing human MVB12 proteins integrate into ESCRT-I despite divergence from yeast Mvb12; human ESCRT-I head includes TSG101–VPS28–VPS37B–MVB12A, supporting conserved family organization relevant to MVB12B (flower2020ahelicalassembly pages 1-2, flower2020ahelicalassembly pages 3-4, souza2010umaandmabp pages 1-2) |
| Key domains | Contains UMA and MABP domains; these domains are implicated in ESCRT-I association and membrane-related trafficking functions | Domain analysis of human MVB12A/B identified UMA and MABP as characteristic features of metazoan MVB12 proteins (souza2010umaandmabp pages 1-2) |
| Complex stoichiometry | ESCRT-I forms a 1:1:1:1 heterotetramer of TSG101:VPS28:VPS37:MVB12 | Hydrodynamic and sedimentation analyses showed soluble human ESCRT-I complexes contain one copy of each subunit type; recombinant complex mass matched a monomeric 1:1:1:1 assembly (morita2007identificationofhuman pages 1-2, morita2007identificationofhuman pages 5-6) |
| Subcellular localization | Predominantly a cytosolic/endosomal trafficking factor that is transiently recruited to endosomal membranes, especially sites of multivesicular body (MVB) / intraluminal vesicle (ILV) formation | ESCRT-I is distributed in cytoplasm at steady state but is recruited to membranes during MVB vesicle formation; ESCRT-I functions in endosomal cargo sorting and ILV biogenesis (morita2007identificationofhuman pages 1-2, vietri2020themanyfunctions pages 1-2) |
| Functional cellular compartment | Acts mainly at early/late endosomal membranes and MVBs where ubiquitinated cargo is sorted toward lysosomal degradation or exosome release | Reviews describe ESCRT-I as a bridge between cargo-recognition systems and downstream ESCRT machinery during MVB biogenesis and exosome-related pathways (vietri2020themanyfunctions pages 1-2, kuchitsu2023stingsignallingis pages 1-2) |
| Post-translational regulation | TBK1-dependent phosphorylation of MVB12B, including S222, regulates its immune-related EV sorting function | In bacterial infection/DNA-stimulation models, MVB12b was identified as a TBK1 phosphotarget, and the S222A mutant impaired the EV-mediated bystander IFN response (nandakumar2019intracellularbacteriaengage pages 1-5, nandakumar2019intracellularbacteriaengage pages 5-15) |
| Specialized regulated function | Phosphorylated MVB12B helps sort DNA into extracellular vesicles/exosomes for paracrine cGAS–STING signaling | MVB12b deficiency or mutation disrupted transfer of IFN-inducing material in EVs from infected or DNA-stimulated donor cells (nandakumar2019intracellularbacteriaengage pages 1-5, nandakumar2019intracellularbacteriaengage pages 5-15) |
| Relationship to broader ESCRT functions | Through ESCRT-I, MVB12B contributes to MVB biogenesis, exosome production, viral budding, cytokinetic abscission, autophagy-linked membrane events, and membrane repair | ESCRT-I is a core upstream module reused across multiple reverse-topology membrane remodeling pathways (vietri2020themanyfunctions pages 1-2, vietri2020themanyfunctions pages 2-3, vietri2020themanyfunctions pages 3-4) |
Table: This table summarizes the verified identity, molecular role, domain architecture, binding partners, localization, stoichiometry, and regulatory phosphorylation of human MVB12B. It is useful as a concise evidence-based reference for functional annotation of Q9H7P6.
| Biological process / pathway | Specific role of MVB12B / ESCRT-I | Key evidence / mechanistic note | Citations |
|---|---|---|---|
| Multivesicular body (MVB) biogenesis and intraluminal vesicle (ILV) formation | MVB12B is a fourth subunit of human ESCRT-I, which acts upstream of ESCRT-II/III during endosomal cargo sorting and ILV formation in MVBs. | Human ESCRT-I is a 1:1:1:1 heterotetramer containing TSG101, VPS28, VPS37 and an MVB12-family subunit; ESCRT-I is recruited to endosomal membranes and helps organize downstream ESCRT assembly for reverse-topology membrane budding. | (flower2020ahelicalassembly pages 1-2, morita2007identificationofhuman pages 1-2, vietri2020themanyfunctions pages 1-2, morita2007identificationofhuman pages 5-6) |
| Exosome biogenesis and secretion | Through its role in ESCRT-I, MVB12B contributes to formation of ILVs within MVBs that can later be secreted as exosomes when MVBs fuse with the plasma membrane. | Reviews of ESCRT-dependent exosome biogenesis place ESCRT-I as a core organizer of ILV generation and exosome production; MVB12-family proteins are part of this machinery in metazoans. | (vietri2020themanyfunctions pages 1-2, kuchitsu2023stingsignallingis pages 1-2) |
| Viral budding and egress (HIV-1) | MVB12B supports ESCRT-I function in HIV-1 budding; perturbing MVB12 proteins disrupts virion release and causes abnormal viral assembly and Gag processing. | Foundational work identified human MVB12 proteins as ESCRT-I subunits required for efficient HIV budding, linking MVB12B directly to viral membrane scission. | (morita2007identificationofhuman pages 1-2, morita2007identificationofhuman pages 5-6) |
| Viral budding and egress (broader ESCRT-dependent viruses) | MVB12B is inferred to contribute when viruses hijack ESCRT-I for budding or egress, because ESCRT-I is a recurrent viral cofactor across enveloped viruses. | Recent reviews emphasize ESCRT-I as a host module used in enveloped virus release; MVB12-family subunits are part of the human ESCRT-I complex that can be co-opted in these contexts. | (flower2020ahelicalassembly pages 1-2, vietri2020themanyfunctions pages 1-2) |
| Innate immune signaling (STING-TBK1-MVB12B axis) | MVB12B is phosphorylated downstream of STING-TBK1 signaling and mediates extracellular-vesicle-based paracrine immune communication. | During intracellular bacterial infection, TBK1-dependent phosphorylation of MVB12B is required for packaging immunostimulatory DNA into extracellular vesicles, enabling bystander cGAS-STING activation. | (nandakumar2019intracellularbacteriaengage pages 1-5, nandakumar2019intracellularbacteriaengage pages 5-15) |
| DNA sorting into extracellular vesicles | MVB12B has a specialized cargo-selection role in sorting DNA into EVs/exosomes, beyond a purely structural ESCRT-I function. | Mvb12b knockout or mutation of the TBK1-regulated phosphorylation site impairs EV-mediated DNA transfer and downstream IFN induction in recipient cells. | (nandakumar2019intracellularbacteriaengage pages 1-5, nandakumar2019intracellularbacteriaengage pages 5-15) |
| Cytokinesis and abscission | MVB12B is not individually singled out in the cited cytokinesis reviews, but as an ESCRT-I subunit it is part of the upstream ESCRT-I module that helps recruit/organize downstream ESCRT-III during abscission. | ESCRT-I is positioned at the top of the abscission pathway, where TSG101 and associated ESCRT-I proteins help nucleate ESCRT-II/III assembly at the midbody. | (vietri2020themanyfunctions pages 1-2, vietri2020themanyfunctions pages 2-3, vietri2020themanyfunctions pages 3-4) |
| Autophagy and lysosomal trafficking | MVB12B likely participates in ESCRT-I-dependent membrane remodeling steps linked to autophagosome closure, endolysosomal trafficking, and cargo delivery to lysosomes. | ESCRT reviews describe ESCRT-I as part of the upstream machinery in autophagy-related and lysosomal trafficking pathways, although the evidence is generally at complex level rather than MVB12B-specific. | (flower2020ahelicalassembly pages 1-2, vietri2020themanyfunctions pages 1-2, kuchitsu2023stingsignallingis pages 1-2) |
| Membrane repair | MVB12B is plausibly involved as an ESCRT-I component in membrane repair pathways that depend on coordinated ESCRT recruitment and remodeling. | Reviews describe ESCRT machinery in membrane sealing/repair; the clearest direct mechanistic assignments are often to ESCRT-III/VPS4, with ESCRT-I acting upstream in recruitment/scaffolding. | (vietri2020themanyfunctions pages 1-2, vietri2020themanyfunctions pages 2-3, vietri2020themanyfunctions pages 3-4) |
Table: This table summarizes the main biological processes linked to human MVB12B as an ESCRT-I subunit, highlighting where evidence is direct for MVB12B versus inferred from ESCRT-I complex biology. It is useful for separating well-supported specialized roles, such as TBK1-dependent DNA sorting into EVs, from broader complex-level functions like cytokinesis and membrane repair.
MVB12B (Q9H7P6) is a canonical human ESCRT-I subunit with central roles in membrane trafficking, exosome/ILV biogenesis, pathogen interaction, and immune regulation. The latest research (2023–2024) highlights its phosphorylation-dependent control of immune vesicle sorting and conserved structural contribution to ESCRT-I function in a variety of essential biological contexts.
This evidence-based functional annotation should serve as a robust and up-to-date resource for research utilizing the human MVB12B gene and protein.
References
(morita2007identificationofhuman pages 1-2): Eiji Morita, Virginie Sandrin, Steven L. Alam, Debra M. Eckert, Steven P. Gygi, and Wesley I. Sundquist. Identification of human mvb12 proteins as escrt-i subunits that function in hiv budding. Cell host & microbe, 2 1:41-53, Jul 2007. URL: https://doi.org/10.1016/j.chom.2007.06.003, doi:10.1016/j.chom.2007.06.003. This article has 174 citations and is from a highest quality peer-reviewed journal.
(flower2020ahelicalassembly pages 1-2): Thomas G. Flower, Yoshinori Takahashi, Arpa Hudait, Kevin Rose, Nicholas Tjahjono, Alexander J. Pak, Adam L. Yokom, Xinwen Liang, Hong-Gang Wang, Fadila Bouamr, Gregory A. Voth, and James H. Hurley. A helical assembly of human escrt-i scaffolds reverse-topology membrane scission. Nature Structural & Molecular Biology, 27:570-580, May 2020. URL: https://doi.org/10.1038/s41594-020-0426-4, doi:10.1038/s41594-020-0426-4. This article has 75 citations and is from a highest quality peer-reviewed journal.
(morita2007identificationofhuman pages 3-5): Eiji Morita, Virginie Sandrin, Steven L. Alam, Debra M. Eckert, Steven P. Gygi, and Wesley I. Sundquist. Identification of human mvb12 proteins as escrt-i subunits that function in hiv budding. Cell host & microbe, 2 1:41-53, Jul 2007. URL: https://doi.org/10.1016/j.chom.2007.06.003, doi:10.1016/j.chom.2007.06.003. This article has 174 citations and is from a highest quality peer-reviewed journal.
(vietri2020themanyfunctions pages 1-2): Marina Vietri, Maja Radulovic, and Harald Stenmark. The many functions of escrts. Nature Reviews Molecular Cell Biology, 21:25-42, Nov 2020. URL: https://doi.org/10.1038/s41580-019-0177-4, doi:10.1038/s41580-019-0177-4. This article has 1079 citations and is from a domain leading peer-reviewed journal.
(morita2007identificationofhuman pages 5-6): Eiji Morita, Virginie Sandrin, Steven L. Alam, Debra M. Eckert, Steven P. Gygi, and Wesley I. Sundquist. Identification of human mvb12 proteins as escrt-i subunits that function in hiv budding. Cell host & microbe, 2 1:41-53, Jul 2007. URL: https://doi.org/10.1016/j.chom.2007.06.003, doi:10.1016/j.chom.2007.06.003. This article has 174 citations and is from a highest quality peer-reviewed journal.
(kuchitsu2023stingsignallingis pages 1-2): Yoshihiko Kuchitsu, Kojiro Mukai, Rei Uematsu, Yuki Takaada, Ayumi Shinojima, Ruri Shindo, Tsumugi Shoji, Shiori Hamano, Emari Ogawa, Ryota Sato, Kensuke Miyake, Akihisa Kato, Yasushi Kawaguchi, Masahiko Nishitani-Isa, Kazushi Izawa, Ryuta Nishikomori, Takahiro Yasumi, Takehiro Suzuki, Naoshi Dohmae, Takefumi Uemura, Glen N. Barber, Hiroyuki Arai, Satoshi Waguri, and Tomohiko Taguchi. Sting signalling is terminated through escrt-dependent microautophagy of vesicles originating from recycling endosomes. Nature Cell Biology, 25:453-466, Mar 2023. URL: https://doi.org/10.1038/s41556-023-01098-9, doi:10.1038/s41556-023-01098-9. This article has 204 citations and is from a highest quality peer-reviewed journal.
(souza2010umaandmabp pages 1-2): Robson F De Souza, L. Aravind, and Alex Bateman. Uma and mabp domains throw light on receptor endocytosis and selection of endosomal cargoes. Bioinformatics, 26:1477-1480, May 2010. URL: https://doi.org/10.1093/bioinformatics/btq235, doi:10.1093/bioinformatics/btq235. This article has 37 citations and is from a highest quality peer-reviewed journal.
(vietri2020themanyfunctions pages 2-3): Marina Vietri, Maja Radulovic, and Harald Stenmark. The many functions of escrts. Nature Reviews Molecular Cell Biology, 21:25-42, Nov 2020. URL: https://doi.org/10.1038/s41580-019-0177-4, doi:10.1038/s41580-019-0177-4. This article has 1079 citations and is from a domain leading peer-reviewed journal.
(vietri2020themanyfunctions pages 3-4): Marina Vietri, Maja Radulovic, and Harald Stenmark. The many functions of escrts. Nature Reviews Molecular Cell Biology, 21:25-42, Nov 2020. URL: https://doi.org/10.1038/s41580-019-0177-4, doi:10.1038/s41580-019-0177-4. This article has 1079 citations and is from a domain leading peer-reviewed journal.
(nandakumar2019intracellularbacteriaengage pages 1-5): Ramya Nandakumar, Roland Tschismarov, Felix Meissner, Thaneas Prabakaran, Abhichart Krissanaprasit, Ensieh Farahani, Bao-cun Zhang, Sonia Assil, Amandine Martin, Wilhelm Bertrams, Christian K. Holm, Andrea Ablasser, Tanja Klause, Martin K. Thomsen, Bernd Schmeck, Kenneth A. Howard, Thomas Henry, Kurt V. Gothelf, Thomas Decker, and Søren R. Paludan. Intracellular bacteria engage a sting–tbk1–mvb12b pathway to enable paracrine cgas–sting signalling. Feb 2019. URL: https://doi.org/10.1038/s41564-019-0367-z, doi:10.1038/s41564-019-0367-z. This article has 144 citations and is from a highest quality peer-reviewed journal.
(nandakumar2019intracellularbacteriaengage pages 5-15): Ramya Nandakumar, Roland Tschismarov, Felix Meissner, Thaneas Prabakaran, Abhichart Krissanaprasit, Ensieh Farahani, Bao-cun Zhang, Sonia Assil, Amandine Martin, Wilhelm Bertrams, Christian K. Holm, Andrea Ablasser, Tanja Klause, Martin K. Thomsen, Bernd Schmeck, Kenneth A. Howard, Thomas Henry, Kurt V. Gothelf, Thomas Decker, and Søren R. Paludan. Intracellular bacteria engage a sting–tbk1–mvb12b pathway to enable paracrine cgas–sting signalling. Feb 2019. URL: https://doi.org/10.1038/s41564-019-0367-z, doi:10.1038/s41564-019-0367-z. This article has 144 citations and is from a highest quality peer-reviewed journal.
(flower2020ahelicalassembly pages 3-4): Thomas G. Flower, Yoshinori Takahashi, Arpa Hudait, Kevin Rose, Nicholas Tjahjono, Alexander J. Pak, Adam L. Yokom, Xinwen Liang, Hong-Gang Wang, Fadila Bouamr, Gregory A. Voth, and James H. Hurley. A helical assembly of human escrt-i scaffolds reverse-topology membrane scission. Nature Structural & Molecular Biology, 27:570-580, May 2020. URL: https://doi.org/10.1038/s41594-020-0426-4, doi:10.1038/s41594-020-0426-4. This article has 75 citations and is from a highest quality peer-reviewed journal.