Falcon (Edison Scientific) deep research report: trpm7 (Danio rerio, UniProt Q563W7) functional annotation.
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TRPM7 is a bifunctional channel-enzyme (chanzyme) comprising a divalent-permeable nonselective cation channel and a cytosolic C-terminal alpha-kinase, matching the UniProt Q563W7 domain architecture and the touchdown/touchtone (tct) zebrafish aliases.
"TRPM7 is often described as a **bifunctional channel-enzyme (chanzyme)**: (i) a **nonselective cation channel** with strong **divalent permeability**, and (ii) a cytosolic **α-kinase** domain that phosphorylates protein substrates on Ser/Thr residues and also autophosphorylates."
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TRPM7 is a plasma-membrane cation channel permeable to Mg2+, Ca2+, and Zn2+ with broader divalent permeability, defining its core transport substrate specificity.
"TRPM7 forms a plasma-membrane cation channel permeable to **Mg2+**, **Ca2+**, and **Zn2+**, with broader permeability to other divalent cations"
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The channel is constitutively active but strongly regulated; intracellular Mg2+ and Mg-ATP are negative regulators and channel opening requires PIP2.
"**Intracellular Mg2+ and Mg·ATP** act as negative regulators."
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The alpha-kinase domain (EC 2.7.11.1) transfers phosphate from ATP to serine/threonine residues of protein substrates and autophosphorylates.
"α-kinase domain transfers phosphate from ATP to **serine/threonine residues** on protein substrates and on TRPM7 itself (autophosphorylation)"
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In zebrafish, touch-evoked escape behavior depends on TRPM7 channel activity, whereas kinase activity and strict divalent-over-monovalent selectivity are dispensable, indicating channel/kinase functions are separable.
"at least one core behavioral function (touch-evoked escape) depends on TRPM7 **channel activity**, whereas TRPM7’s **kinase activity** and strict preference for divalents over monovalents were reported to be **dispensable** for that behavior"
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Touchdown (trpm7) mutants show a transient touch-evoked escape deficit between 52 and 63 hpf (n = 24 embryos from three clutches), with the defect downstream of intact, tactile-responsive sensory neurons.
"they **do not respond between 52 and 63 hours post-fertilization (hpf)** (reported **n = 24 embryos from three clutches**)"
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trpm7 mRNA is broadly expressed in zebrafish with high abundance in pronephric/mesonephric kidney tubules and the corpuscles of Stannius, consistent with a primary role in systemic divalent-cation regulation and renal physiology.
"In zebrafish, **trpm7 mRNA is broadly expressed**, with particularly high abundance in **kidney tubules** (pronephric/mesonephric) and in the **corpuscles of Stannius** (an endocrine organ involved in ionic homeostasis), supporting a primary role in systemic divalent-cation regulation and renal physiology"
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trpm7 mutants show reduced whole-embryo total magnesium and calcium, kidney stone formation, and altered stc1/fgf23 endocrine programs; fgf23 knockdown reduces kidney stones.
"Mutants also exhibit **kidney stone formation** and altered endocrine programs involving **stanniocalcin 1 (stc1)** and **fgf23**; mechanistically, **fgf23 knockdown reduces kidney stones**"
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Melanophore loss in trpm7 mutants occurs by necrosis rather than caspase-dependent apoptosis, and inhibition of melanin synthesis largely prevents melanophore death.
"In **trpm7 mutant embryos**, melanophore loss results from **cell death with necrotic features** (not caspase-dependent apoptosis)."
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TRPM7 is a tetrameric plasma-membrane channel; 2023 cryo-EM structures (2.17-2.99 Angstrom) resolved closed and open conformations and druggable agonist/inhibitor pockets.
"Cryo-EM structures in 2023 resolved TRPM7 at **2.17-2.99 Å**"