MgtE (PA0913) is the Pseudomonas aeruginosa PAO1 inner-membrane magnesium transporter of the MgtE/SLC41 family. It has a cytoplasmic N domain and two CBS domains joined to a C-terminal transmembrane domain by a connecting helix. In the Thermus thermophilus homologue this architecture forms a homodimeric Mg2+-selective channel. Mg2+ bound at sites between the cytoplasmic domains holds the pore shut, so the channel senses intracellular Mg2+ and admits more when Mg2+ is low; most of these Mg2+ ligands, including the pore aspartate, are conserved in PA0913. P. aeruginosa MgtE transports Mg2+, is not essential, and is induced under low Mg2+. It also dampens type III secretion. mgtE mutants show more T3SS transcription and more cytotoxicity toward airway epithelial cells, and mgtE expression acts through the GacAS-rsmY/rsmZ pathway to inhibit exsA translation. Variants defective in Mg2+ transport can still suppress cytotoxicity, and the Mg2+-binding sites of the connecting helix are needed to couple transport to this regulatory output.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000287 magnesium ion binding | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA from PTN000227060, the root of PTHR43773 (25 eubacterial reference leaves), seeded only by the PseudoCAP IMP row for this gene. MgtE does bind Mg2+: it is both the transported ion and the ligand of the cytosolic sensor sites and the pore aspartate in the T. thermophilus structures. Most of those ligands are conserved in PA0913. Reason: True by similarity, so kept. Mg2+ binding is part of the transport and gating mechanism, not a separate function. The IBD rests on a seed that is not binding evidence (see the IMP row). The family member with direct binding data (Q5SMG8) is not a tree leaf, so it cannot re-seed the node. Propagation Review Root cause: SOURCE WEAK OR INFERRED Sources checked: PANTHER:PTN000227060 · PTN000227060 SUPPORTS TRANSFER Family-root node; Mg2+ binding is plausible for the clade because the N/CBS sensor domains and, in full-length members, the pore are conserved. Not checked for the TM-less leaves. UniProtKB:Q9I544 · mgtE (PA0913) SOURCE WEAK OR INFERRED Sole seed; the PseudoCAP row is IMP from site-directed mutants of predicted sites, which shows the residues matter but not that they bind Mg2+. Supporting Evidence: PMID:17700703 Four putative Mg2+ ions are bound at the interface between the connecting helices and the other domains, and this may lock the closed conformation of the pore. file:PSEAE/mgtE/mgtE-bioinformatics/RESULTS.md The Mg2+-binding apparatus of the Tth channel, including the pore aspartate and most acidic cytosolic sensor ligands, is conserved in PA0913 |
| GO:0000287 magnesium ion binding | IMP PMID:24722909 MgtE is a dual-function protein in Pseudomonas aeruginosa. | KEEP AS NON CORE | Summary: PseudoCAP IMP, the sole seed of the PTN000227060 Mg2+-binding IBD. Coffey et al. modelled P. aeruginosa MgtE on the T. thermophilus crystal structure and showed that the Mg2+-binding sites of the connecting helix, as identified in that model, are needed to couple transport to cytotoxicity regulation. The abstract reports no direct binding measurement. The full text was not available. Reason: The binding claim is true by similarity (structure of the orthologue; conserved ligands), so the annotation is kept. But a mutant phenotype cannot show ion binding: the experimental part of this row supports a role for the residues, not binding. Flagged to PseudoCAP for an evidence check. Supporting Evidence: PMID:24722909 Our in silico analysis demonstrated the structural similarity of P. aeruginosa MgtE to that of the crystal structure of MgtE in Thermus thermophilus. PMID:24722909 showed that magnesium-binding sites in the connecting helix region of MgtE are vital in coupling these two functions |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniRule subcellular location (cell membrane, multi-pass). MgtE is described as an inner-membrane protein, and its transmembrane domain is predicted. Reason: Correct location for a cytoplasmic-membrane Mg2+ transporter of a Gram-negative bacterium. Supporting Evidence: PMID:24722909 We previously found that the inner-membrane protein MgtE can function both as a magnesium transporter and a virulence modulator |
| GO:0006812 monoatomic cation transport | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO from the SLC41 membrane domain. Correct but general. Reason: True but general; the specific process, GO:1903830 magnesium ion transmembrane transport (a descendant, already on this gene by IEA), is supported. Proposed replacements: magnesium ion transmembrane transport Supporting Evidence: PMID:24722909 We demonstrated both magnesium transport and cytotoxicity-regulating functions |
| GO:0008324 monoatomic cation transmembrane transporter activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO from the SLC41 membrane domain. Correct but general. Reason: True but general; GO:0015095 magnesium ion transmembrane transporter activity (an is_a descendant via metal ion transmembrane transporter activity, already on this gene) is supported. Proposed replacements: magnesium ion transmembrane transporter activity Supporting Evidence: PMID:24722909 We demonstrated both magnesium transport and cytotoxicity-regulating functions |
| GO:0015095 magnesium ion transmembrane transporter activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined InterPro/UniRule assignment for the MgtE family. P. aeruginosa MgtE transports Mg2+, and its Thermus orthologue is a Mg2+-selective channel. Reason: Core activity. GO has no Mg2+-specific channel term, so this is the most specific suitable MF. Supporting Evidence: PMID:24722909 We demonstrated both magnesium transport and cytotoxicity-regulating functions PMID:19798051 Here, we showed that MgtE is a highly Mg(2+)-selective channel gated by Mg(2+) |
| GO:0015693 magnesium ion transport | IBA GO_REF:0000033 | MODIFY | Summary: IBA from PTN000227060 (PTHR43773 family root), sole-seeded by the PseudoCAP IMP row for this gene. Correct for PA0913, which has the full transmembrane domain. Six of the reference leaves lack the MgtE transmembrane domain, though, and inherit this transport IBA anyway. Reason: Correct but general for this gene; GO:1903830 magnesium ion transmembrane transport (is_a descendant, already on this gene by IEA) is the specific process. The node placement problem (TM-less leaves) does not affect PA0913 and is recorded as a GO_CENTRAL defect. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000227060 · PTN000227060 SUPPORTS TRANSFER Right for the full-length MgtE transporters that make up most of the clade; over-propagated to six leaves that lack PF01769. UniProtKB:Q9I544 · mgtE (PA0913) SUPPORTS TRANSFER Sole seed; Mg2+ transport by P. aeruginosa MgtE is reported in PMID:24722909 and PMID:20028803. Proposed replacements: magnesium ion transmembrane transport Supporting Evidence: PMID:24722909 We demonstrated both magnesium transport and cytotoxicity-regulating functions file:PSEAE/mgtE/mgtE-bioinformatics/RESULTS.md Of the 22 leaves resolved in UniProt, 16 carry Pfam PF01769 (MgtE transmembrane domain) and 6 do not |
| GO:0015693 magnesium ion transport | IEA GO_REF:0000120 | MODIFY | Summary: Combined InterPro/UniRule assignment for the MgtE family; agrees with the IBA and IMP rows. Reason: Correct but general; GO:1903830 magnesium ion transmembrane transport (is_a descendant, already on this gene) is the specific process. Proposed replacements: magnesium ion transmembrane transport Supporting Evidence: PMID:24722909 We demonstrated both magnesium transport and cytotoxicity-regulating functions |
| GO:0015693 magnesium ion transport | IMP PMID:24722909 MgtE is a dual-function protein in Pseudomonas aeruginosa. | MODIFY | Summary: PseudoCAP IMP, the sole seed of the PTN000227060 magnesium ion transport IBD. Coffey et al. report that P. aeruginosa MgtE transports Mg2+ (the assay is not given in the abstract). The earlier paper from the same group describes mgtE variants defective for Mg2+ transport. This is the gene's own transport process, not an indirect phenotype. Reason: Sound seed; the process term is correct but general for a transmembrane transporter. GO:1903830 (is_a descendant, already on this gene) is the specific term. Proposed replacements: magnesium ion transmembrane transport Supporting Evidence: PMID:24722909 We demonstrated both magnesium transport and cytotoxicity-regulating functions PMID:20028803 mgtE variants that were defective for magnesium transport could still complement the cytotoxicity effect |
| GO:0016020 membrane | IEA GO_REF:0000120 | MODIFY | Summary: Generic membrane location from the family and keyword mappings. Reason: True but general; GO:0005886 plasma membrane (already on this gene) is the supported location for this inner-membrane transporter. Proposed replacements: plasma membrane Supporting Evidence: PMID:24722909 We previously found that the inner-membrane protein MgtE can function both as a magnesium transporter and a virulence modulator |
| GO:0098655 monoatomic cation transmembrane transport | IEA GO_REF:0000108 | MODIFY | Summary: Inferred from the general cation transporter MF. Correct but general. Reason: True but general; GO:1903830 magnesium ion transmembrane transport (is_a descendant, already on this gene) is supported. Proposed replacements: magnesium ion transmembrane transport Supporting Evidence: PMID:24722909 We demonstrated both magnesium transport and cytotoxicity-regulating functions |
| GO:1903830 magnesium ion transmembrane transport | IEA GO_REF:0000108 | ACCEPT | Summary: Inferred from GO:0015095. Mg2+ movement across the inner membrane is the transporter's own process. Reason: Core process; the most specific supported BP term. Supporting Evidence: PMID:24722909 We demonstrated both magnesium transport and cytotoxicity-regulating functions |
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Download this section (compressed HTML)Q: Does P. aeruginosa MgtE bind Mg2+ at the conserved cytosolic and pore sites, as the Thermus structures predict? A direct binding measurement would let the PTN000227060 Mg2+-binding IBD rest on experimental evidence.
Q: How does a membrane Mg2+ transporter signal to GacAS to raise rsmY/rsmZ, and is that output separable from transport?
Q: Should the TM-less MgtE_N/CBS proteins of PTHR43773 (SCO5154, Rv1232c, CBO0203, TM_0892, VC_0300) carry NOT magnesium ion transport, and do they bind Mg2+ as soluble sensors?
Experiment: Measure Mg2+ binding by purified P. aeruginosa MgtE cytosolic domain (ITC or tryptophan fluorescence), wild type against the connecting-helix site mutants of Coffey et al. Also measure Mg2+ uptake (for example 25Mg/63Ni or mag-fura-2 assays) in a Mg2+-transport-deficient host. This would separate binding, gating and transport for this orthologue.
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