| Claim/Concept | Current understanding (1-2 sentences) | Key evidence/assay type | Key sources (include year, journal) | URL |
|---|---|---|---|---|
| Identity / synonyms | Human **MMGT1** (UniProt **Q8N4V1**) is the same protein widely referred to in the literature as **EMC5** and also as **TMEM32**. Reviews and primary papers explicitly identify EMC5/MMGT1 as a small (~15 kDa) subunit of the ER membrane protein complex (EMC), not a separate unrelated protein. (pqac-00000000, pqac-00000001, pqac-00000014) | Complex annotation, purification/proteomics, review synthesis of EMC subunits | Chitwood & Hegde, **2019**, *Trends in Cell Biology*; Rother & Naumann, **2021**, *Virus Research* | https://doi.org/10.1016/j.tcb.2019.01.007 ; https://doi.org/10.1016/j.virusres.2021.198338 |
| Localization: ER membrane; EMC complex | MMGT1/EMC5 is an **integral ER membrane** protein and one of the membrane-embedded EMC subunits. Mammalian EMC is an abundant ER-resident multi-subunit complex whose membrane subunits collectively form the transmembrane region involved in client handling. (pqac-00000000, pqac-00000005, pqac-00000014) | Subcellular complex purification, topology prediction, cryo-EM structural mapping | Chitwood & Hegde, **2019**, *Trends in Cell Biology*; Li et al., **2024**, *Aging (Albany NY)* | https://doi.org/10.1016/j.tcb.2019.01.007 ; https://doi.org/10.18632/aging.205660 |
| Role in EMC stability | EMC5 is considered a **core EMC subunit**: individual depletion/knockout of EMC5 strongly disrupts integrity of the remaining complex, and CRISPR knockout can cause near-complete loss of other EMC subunits. This indicates MMGT1/EMC5 is structurally required for stable EMC assembly rather than being a peripheral accessory factor. (pqac-00000001, pqac-00000002, pqac-00000014) | Knockdown/CRISPR knockout with assessment of other subunits and complex integrity | Chitwood & Hegde, **2019**, *Trends in Cell Biology* | https://doi.org/10.1016/j.tcb.2019.01.007 |
| Role in membrane protein insertion / topogenesis | The strongest current functional assignment for MMGT1 is **as part of EMC**, a membrane-protein insertase/chaperone system that mediates insertion or topogenesis of low-hydrophobicity tail-anchored proteins and selected transmembrane domains of multipass proteins. EMC loss causes reduced client maturation, ER retention, topology defects, and altered expression of multipass membrane proteins; these phenotypes are attributed to the EMC machinery in which EMC5 is a core membrane subunit. (pqac-00000002, pqac-00000003, pqac-00000004, pqac-00000008) | In vitro liposome reconstitution, cell-free microsome assays, split-GFP insertion assays, crosslinking, client maturation/localization phenotypes | Chitwood & Hegde, **2019**, *Trends in Cell Biology*; Pleiner et al., **2023**, *Journal of Cell Biology*; Wu et al., **2024**, *Nature Structural & Molecular Biology* | https://doi.org/10.1016/j.tcb.2019.01.007 ; https://doi.org/10.1083/jcb.202212007 ; https://doi.org/10.1038/s41594-023-01120-6 |
| Structural features: hydrophilic vestibule; relation to EMC3/6 cavity; tagging/purification via EMC5 | Structural studies place EMC5 in the **membrane module** of EMC, contributing with EMC1/3/6 to a membrane cavity or lipid-filled region adjacent to the hydrophilic vestibule used for client insertion/topology control. Human EMC has also been purified through **tagged EMC5** (for example, Twin-Strep/FLAG strategies), showing EMC5 is experimentally tractable as a stable core handle for native EMC purification. (pqac-00000007, pqac-00000009, pqac-00000016) | Cryo-EM, native complex purification, tagged endogenous EMC5 purification schemes | Li et al., **2024**, *Aging (Albany NY)*; Klose et al., **2025**, *Nature Communications* | https://doi.org/10.18632/aging.205660 ; https://doi.org/10.1038/s41467-025-62109-x |
| Relation to viral infection | MMGT1/EMC5 has been recovered in host-factor studies as part of the **EMC dependency** of flaviviruses and other viruses that require ER biogenesis of viral multi-pass membrane proteins. The evidence supports an **indirect role via EMC-mediated membrane protein biogenesis**, not a virus-specific activity intrinsic to EMC5 alone. (pqac-00000000, pqac-00000014) | CRISPR or RNAi host-factor screens; infection phenotypes linked to EMC disruption | Rother & Naumann, **2021**, *Virus Research*; Chitwood & Hegde, **2019**, *Trends in Cell Biology* | https://doi.org/10.1016/j.virusres.2021.198338 ; https://doi.org/10.1016/j.tcb.2019.01.007 |
| Relation to *Mycobacterium tuberculosis* persistence and lipid droplets | A 2023 CRISPR-screen study prioritized MMGT1 for follow-up and found that **MMGT1-deficient macrophages** promoted an *M. tuberculosis* switch toward persistence, with upregulation of lipid metabolism genes and increased lipid droplets; triacylglycerol synthesis inhibition reduced both droplet formation and persistence. This is a real host-pathogen phenotype linked to MMGT1, but the study does **not** by itself prove whether the underlying mechanism is magnesium transport, EMC function, or another MMGT1-dependent pathway. (pqac-00000012, pqac-00000013) | Genome-wide CRISPR screen, CFU time courses, RNA-seq/GSEA, qPCR, confocal imaging, FACS lipid-droplet quantification | Kalam et al., **2023**, *Cell Host & Microbe* | https://doi.org/10.1016/j.chom.2023.05.009 |
| Magnesium transport evidence and caveats | MMGT1 was originally named a **membrane magnesium transporter**, but current evidence is mixed and weaker than the EMC evidence. Authoritative review literature explicitly states that for **MMgT/MMGT1**, functional evidence for bona fide Mg2+ transport is limited and alternative functions have been suggested; EMC-focused reviews note that reported Mg2+ transport upon overexpression may be unrelated to EMC’s core biogenesis role. (pqac-00000002, pqac-00000015) | Critical review of transporter literature; comparison of direct transport evidence versus alternative cell-biological roles | Schäffers et al., **2018**, *American Journal of Physiology-Renal Physiology*; Chitwood & Hegde, **2019**, *Trends in Cell Biology* | https://doi.org/10.1152/ajprenal.00634.2017 ; https://doi.org/10.1016/j.tcb.2019.01.007 |


*Table: This table summarizes the best-supported functional annotation for human MMGT1/EMC5/TMEM32, emphasizing evidence that it is a core ER membrane subunit of the EMC complex involved in membrane protein biogenesis. It also highlights newer disease/infection-related findings and the important caveat that direct magnesium-transport evidence remains limited.*