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Showing SLC9B2 — NHA2 is a alias.

SLC9B2

Sodium/hydrogen exchanger 9B2 · UniProt Q86UD5

Length
537 aa
Mass
57.6 kDa
Annotated
2026-06-10
20 papers in source corpus 15 papers cited in narrative 15 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/7 claims corpus-supported (86%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SLC9B2/NHA2 is an electroneutral Na+(Li+)/H+ antiporter that supports ion and volume homeostasis across multiple specialized epithelia and secretory cells (PMID:18508966, PMID:22948142). It performs bona fide Na+/H+ exchange, demonstrated by functional complementation of exchanger-null yeast (PMID:18508966), and at the mammalian plasma membrane it operates as a phloretin-sensitive Na+-Li+ countertransporter coupled to a V-ATPase-generated H+ gradient, effectively functioning as a virtual Na+ efflux pump (PMID:22948142). Cryo-EM of human NHA2 revealed a distinctive 14-transmembrane-helix homodimer with a D278–R432 ion-binding-site salt bridge implicated in ion coupling and phosphatidic acid bound at the dimer interface (PMID:40362458); consistent functional mutagenesis identifies P246 as a determinant of ion selectivity, the E215/R432 salt bridge as required for activity and structural integrity, and a hydrophilic N-terminal domain that allosterically auto-inhibits transport (PMID:36177733). Plasma-membrane delivery of NHA2 requires cornichon COPII cargo receptors (yeast Erv14 and human CNIH1/2/4) for ER exit (PMID:41676957). In the kidney, NHA2 localizes to distal convoluted tubule and connecting tubule cells, is regulated by dietary sodium, and controls blood pressure through the WNK4–SPAK–NCC pathway: NHA2 loss increases KLHL3-mediated WNK4 ubiquitylation and degradation, reducing SPAK/NCC phosphorylation, an effect confirmed NCC-dependent by double-knockout epistasis (PMID:27909897, PMID:32956652). In pancreatic β-cells, NHA2 resides in transferrin-positive endosomes and synaptic-like microvesicles and is required for clathrin-dependent endocytosis and endo-exocytosis coupling, with its loss causing impaired insulin secretion and glucose intolerance (PMID:23720317). NHA2 expression is also induced during RANKL-driven osteoclast differentiation downstream of Brd4 (PMID:41115147), and its renal expression is regulated by polycystin-1/NFAT, vasopressin, and methylxanthines, where ectopic NHA2 promotes cystogenesis (PMID:30242840).

Mechanistic history

Synthesis pass · year-by-year structured walk · 15 steps
  1. 2007 Medium

    Established the first functional context for NHA2, linking it to osteoclast differentiation and bone resorption and proposing a mitochondrial role.

    Evidence RANKL differentiation assays, mitochondrial pH/swelling assays, and siRNA knockdown in osteoclasts

    PMID:17988971

    Open questions at the time
    • Mitochondrial localization was later contradicted
    • No direct biochemical demonstration of antiporter activity in this study
  2. 2008 High

    Demonstrated that NHA2 is a genuine Na+/H+ exchanger and defined its restricted distal-tubule expression, anchoring the protein as a functional antiporter.

    Evidence cDNA cloning, yeast complementation of NHE-null strains, immunogold EM and fractionation in kidney

    PMID:18508966

    Open questions at the time
    • Reported mitochondrial co-localization conflicted with later studies
    • Transport stoichiometry and directionality not resolved
  3. 2010 High

    Resolved the localization controversy and tested in vivo necessity, reassigning NHA2 to endo-lysosomal and basolateral plasma membranes and showing it is dispensable for bone resorption.

    Evidence Confocal co-localization with LAMP1/V-ATPase a3, surface biotinylation, and micro-CT phenotyping of NHA2-KO mice

    PMID:20441802

    Open questions at the time
    • Does not explain the earlier siRNA osteoclast phenotype
    • Functional role at the basolateral membrane left open
  4. 2010 Medium

    Identified specific transmembrane residues essential for antiporter activity, beginning the structure-function dissection of NHA2.

    Evidence Site-directed mutagenesis (V161, F357, F437) in salt-sensitive yeast with atomic absorption Na+ measurement

    PMID:20713131

    Open questions at the time
    • No structural model to interpret residue positions
    • Performed only in heterologous yeast
  5. 2012 Medium

    Defined the transport mode at the mammalian plasma membrane, showing NHA2 is H+-gradient-coupled rather than Na+-coupled.

    Evidence Na+-Li+ countertransport assay in MDCK cells with phloretin and V-ATPase inhibitors

    PMID:22948142

    Open questions at the time
    • Single cell-line system
    • Quantitative coupling stoichiometry not established
  6. 2013 High

    Established a physiological role for NHA2 in insulin secretion via endosomal trafficking, linking transport activity to endo-exocytosis coupling.

    Evidence NHA2-KO glucose/insulin tests, β-cell subcellular fractionation, clathrin-dependent endocytosis assays, rescue with wild-type vs functionally dead transporter

    PMID:23720317

    Open questions at the time
    • How ion transport mechanistically drives clathrin-dependent endocytosis is unresolved
    • Identity of relevant endosomal ion gradient not defined
  7. 2015 High

    Confirmed conserved Na+/H+ exchange function and in vivo importance for Na+ homeostasis using an invertebrate ortholog.

    Evidence Xenopus oocyte transport assays and Drosophila Nha1/Nha2 RNAi epistasis under ionic stress

    PMID:26324901

    Open questions at the time
    • Direct mammalian in vivo Na+ homeostasis link not addressed here
    • Tissue-specific contributions not separated
  8. 2016 Medium

    Refined renal localization to apical DCT/connecting tubule and identified dietary sodium as a transcriptional regulator of NHA2.

    Evidence Immunohistochemistry with V-ATPase/AQP2/NCC co-markers and qPCR/immunoblot after dietary NaCl manipulation in mouse kidney

    PMID:27909897

    Open questions at the time
    • Transcriptional regulators mediating dietary response unknown
    • Functional consequence of apical localization not tested
  9. 2018 Medium

    Placed NHA2 within polycystin-1/NFAT signaling and implicated it in renal cystogenesis.

    Evidence MDCK 3D cyst model with NHA2 gain/loss-of-function, PC1 induction/dominant-negative, NFAT reporter, vasopressin/methylxanthine treatment

    PMID:30242840

    Open questions at the time
    • In vivo relevance to polycystic kidney disease not established
    • Transport-dependence of cystogenic effect not fully isolated
  10. 2020 High

    Defined a mechanistic role for NHA2 in blood pressure control through stabilization of WNK4 via KLHL3, linking the transporter to NCC regulation.

    Evidence NHA2-KO and NHA2/NCC double-KO mice, blood pressure and thiazide challenge, WNK4 ubiquitylation and SPAK/NCC phosphorylation assays, KLHL3 phosphorylation assay

    PMID:32956652

    Open questions at the time
    • How NHA2 transport activity signals to KLHL3 phosphorylation is unclear
    • Direct physical interaction with WNK4/KLHL3 not demonstrated
  11. 2022 Medium

    Mapped determinants of ion selectivity, structural integrity, and identified N-terminal autoinhibition, advancing the structure-function model.

    Evidence Site-directed mutagenesis (P246, E215/R432) and N-terminal truncations in yeast with functional and localization readouts

    PMID:36177733

    Open questions at the time
    • Autoinhibition lacked structural visualization
    • Heterologous-system only
  12. 2024 Medium

    Identified residues governing phloretin binding, refining the pharmacology of NHA2 inhibition.

    Evidence Bioinformatic modeling and R177/S178 mutagenesis with phloretin inhibition assays in yeast

    PMID:39737617

    Open questions at the time
    • Inhibitor pose not experimentally confirmed at the time
    • Single heterologous system
  13. 2025 High

    Provided near-atomic architecture of human NHA2, revealing a unique 14-TM fold, lipid binding, and a candidate ion-coupling salt bridge.

    Evidence Cryo-EM of apo and phloretin-bound human NHA2 with Fab assistance and comparison to bison NHA2

    PMID:40362458

    Open questions at the time
    • Conformational transport cycle not captured
    • Functional role of phosphatidic acid in volume regulation not validated in cells
  14. 2025 Medium

    Identified Brd4 as a transcriptional activator of NHA2 in osteoclast metabolism and differentiation.

    Evidence Conditional Brd4-KO mice, transcriptomic screening, and Slc9b2 overexpression rescue of impaired osteoclastogenesis

    PMID:41115147

    Open questions at the time
    • Direct Brd4 occupancy at the Slc9b2 locus not shown
    • Mechanistic link between NHA2 transport and glycolysis undefined
  15. 2026 Medium

    Defined the ER-exit machinery for NHA2 surface delivery, identifying cornichon COPII cargo receptors as trafficking partners.

    Evidence Heterologous expression in yeast with ScErv14 replacement by human CNIH1/2/4, plasma-membrane targeting and complementation assays, AlphaFold3 modeling

    PMID:41676957

    Open questions at the time
    • Cornichon dependence not validated in mammalian cells in vivo
    • Direct NHA2-cornichon binding interface not experimentally resolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • How NHA2 transport activity is mechanistically coupled to its diverse cellular roles—endo-exocytosis in β-cells, WNK4/KLHL3 signaling in kidney, and osteoclast metabolism—remains unresolved.
  • No direct demonstration of how ion transport feeds into WNK4 stabilization
  • Transport cycle and conformational states not structurally resolved
  • Physical interactions with downstream signaling proteins undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005215 transporter activity 3 GO:0140104 molecular carrier activity 2
Localization
GO:0005886 plasma membrane 3 GO:0005764 lysosome 1 GO:0005768 endosome 1 GO:0031410 cytoplasmic vesicle 1
Pathway
R-HSA-382551 Transport of small molecules 2 R-HSA-162582 Signal Transduction 1 R-HSA-5653656 Vesicle-mediated transport 1
Partners
CNIH1CNIH2CNIH4KLHL3WNK4

Evidence

Reading pass · 15 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2008 Human NHA2 (SLC9B2) was cloned from a brain cDNA library and characterized as a ~55 kDa sodium/proton exchanger expressed in multiple mammalian tissues. In kidney, NHA2 was restricted to the distal convoluted tubule and co-localized with the mitochondrial inner membrane marker by immunogold EM and differential centrifugation. NHA2 functionally complemented sodium/hydrogen exchanger-null yeast (restored growth under high NaCl at acidic pH), demonstrating bona fide Na+/H+ exchange activity. cDNA cloning, immunoblot with siRNA validation, co-sedimentation/differential centrifugation, immunogold EM, heterologous expression in NHE-deficient yeast Journal of the American Society of Nephrology High 18508966
2007 NHA2 (NHA-oc/NHA2) is strongly upregulated during RANKL-induced osteoclast differentiation in vitro and in vivo. The protein localizes to mitochondria in osteoclasts, where it mediates Na+-dependent changes in mitochondrial pH and Na+-acetate-induced mitochondrial passive swelling. siRNA silencing of NHA2 reduced osteoclast differentiation and bone resorption in vitro. RANKL-stimulated differentiation assay, mitochondrial pH assay, mitochondrial swelling assay, siRNA knockdown, microarray followed by Northern blot and in situ hybridization Bone Medium 17988971
2010 Using NHA2-specific antibodies and NHA2-deficient mice, NHA2 was found to co-localize with the late endosomal/lysosomal marker LAMP1 and V-ATPase a3 subunit (not mitochondrial markers) in osteoclasts. Surface biotinylation and immunofluorescence further showed NHA2 is highly enriched at the plasma membrane, specifically the basolateral membrane of polarized osteoclasts. Contrary to earlier siRNA data, NHA2-deficient mice showed no difference in bone parameters, osteoclast development, or resorption activity in vitro, indicating NHA2 is dispensable for osteoclast differentiation and bone resorption. Confocal microscopy, subcellular fractionation, surface biotinylation, microcomputed tomography of NHA2-KO mice, in vitro RANKL stimulation of KO bone marrow cells Bone High 20441802
2012 Human NHA2 mediates phloretin-sensitive Na+-Li+ countertransport (SLC) activity at the plasma membrane of kidney-derived MDCK cells, coupled to a plasma membrane H+ gradient generated by V-type H+-ATPase, functioning as a virtual Na+ efflux pump. This establishes H+-coupled (rather than Na+-coupled) secondary transport for NHA2 at the mammalian plasma membrane. Na+-Li+ countertransport assay in MDCK cells, pharmacological inhibition with phloretin, V-ATPase inhibitor studies Journal of Biological Chemistry Medium 22948142
2013 NHA2 is present in rodent and human β-cells and resides in transferrin-positive endosomes and synaptic-like microvesicles (not large dense core vesicles). NHA2-deficient mice show impaired insulin secretion and glucose intolerance. Loss of NHA2 inhibited clathrin-dependent but not clathrin-independent endocytosis in Min6 and primary β-cells, implicating defective endo-exocytosis coupling as the mechanism for impaired secretion. The secretory deficit was rescued by wild-type but not functionally dead NHA2. NHA2-KO mouse in vivo glucose tolerance/insulin secretion tests, subcellular fractionation and confocal imaging, clathrin-dependent endocytosis assay, rescue by wild-type vs. functionally dead transporter overexpression, NHA2 inhibitor treatment of isolated islets Proceedings of the National Academy of Sciences USA High 23720317
2010 Mutational analysis in NHA2 expressed in salt-sensitive S. cerevisiae identified residues V161 and F357 as required for Na+ efflux and growth on NaCl medium; the double mutant F357/F437 abolished growth on 0.4 M NaCl, demonstrating these evolutionarily conserved residues are essential for antiporter activity. Heterologous expression in salt-sensitive S. cerevisiae (BW31a), atomic absorption spectroscopy for intracellular Na+, growth assays on NaCl medium, confocal microscopy of membrane expression Biochimica et Biophysica Acta Medium 20713131
2015 In Drosophila, Nha2 (Slc9b2 ortholog) expressed in Xenopus oocytes functions as a Na+/H+ exchanger (in contrast to Nha1 which acts as an H+-Cl- cotransporter). RNAi knockdown of Nha2 alone reduces survival; combined knockdown of Nha1 and Nha2 is lethal; under NaCl but not KCl stress, Nha2 knockdown decreases survival, demonstrating a specific role in Na+ homeostasis. Xenopus oocyte functional expression assay, Drosophila RNAi knockdown survival assay, ion stress experiments Proceedings of the National Academy of Sciences USA High 26324901
2016 In murine kidney, NHA2 localizes apically to distal convoluted tubules (DCT1 and DCT2) and connecting tubules, partially overlapping with V-ATPase, AQP2, and NCC1. Dietary high-NaCl elevated NHA2 transcript and protein levels, establishing dietary sodium as a regulator of NHA2 expression in the kidney. Immunohistochemistry/confocal microscopy in murine kidney sections, quantitative PCR and immunoblot after dietary NaCl manipulation Journal of Physiology and Biochemistry Medium 27909897
2018 NHA2 is transcriptionally regulated by Ca2+/NFAT signaling downstream of polycystin-1 (PC1): induction of PC1 inhibited NHA2 expression, whereas the dominant-negative PC1-MAT fragment elevated NHA2. Ectopic NHA2 expression in MDCK 3D cultures increased cyst size, and siRNA silencing or pharmacological inhibition of NHA2 inhibited cyst formation. NHA2 was also transcriptionally induced by vasopressin and methylxanthines (caffeine, theophylline). MDCK 3D cystogenesis model, NHA2 overexpression and siRNA silencing, PC1 induction/dominant-negative experiments, pharmacological inhibition of NHA2, NFAT reporter assay, vasopressin/drug treatment Journal of Physiology Medium 30242840
2020 NHA2 localizes almost exclusively to distal convoluted tubules in the kidney and regulates blood pressure via the WNK4-NCC pathway. NHA2-KO mice showed reduced blood pressure, hypocalciuria, and attenuated thiazide response. Loss of NHA2 increased WNK4 ubiquitylation and proteasomal degradation, reducing WNK4 abundance and consequently SPAK and NCC phosphorylation. This effect required KLHL3, as NHA2 loss selectively attenuated KLHL3 phosphorylation, blunting PKA- and PKC-mediated protection of WNK4. NHA2/NCC double-KO phenotype analysis confirmed NCC-dependent blood pressure regulation by NHA2. NHA2-KO and NHA2/NCC double-KO mouse models, blood pressure measurement, thiazide challenge, ubiquitylation assay, immunoblot for WNK4/SPAK/NCC phosphorylation, in vitro cell experiments, KLHL3 phosphorylation assay Kidney International High 32956652
2022 Mutational analysis in S. cerevisiae identified proline P246 in the transmembrane core as crucial for ion selectivity: P246S/T substitutions produced antiporters active at both acidic and neutral pH with altered substrate specificity and reduced phloretin sensitivity. A putative salt bridge between E215 and R432 is required for both antiporter function and structural integrity. Truncation of the first 50–70 N-terminal residues doubled transport activity, demonstrating that the hydrophilic N-terminal domain allosterically auto-inhibits cation transport of NHA2. Site-directed mutagenesis, N-terminal truncations expressed in S. cerevisiae, functional growth assays on NaCl medium, localization by fluorescence microscopy, phloretin inhibition assay Protein Science Medium 36177733
2024 Residues R177 and S178 of NHA2 are involved in phloretin binding/inhibition: R177T mutation reduced phloretin sensitivity, while S178T enhanced inhibition, as demonstrated by site-directed mutagenesis and functional expression in S. cerevisiae. Bioinformatic modeling, site-directed mutagenesis, functional expression in S. cerevisiae, phloretin inhibition assay FEBS Letters Medium 39737617
2025 Cryo-EM structures of human NHA2 (apo + Fab and phloretin-bound) at 2.8–2.9 Å resolution revealed a unique 14-transmembrane helix architecture distinct from SLC9A/NHE members. Phosphatidic acid (PA) lipids bind the homodimer interface on the extracellular side, proposed to have a regulatory role in cell volume regulation. The ion-binding site contains a salt bridge between D278 and R432; this interaction is broken in the bison NHA2 structure, suggesting a possible ion coupling mechanism. The phloretin-bound structure provides a template for structure-guided inhibitor design. Cryo-electron microscopy, Fab-assisted structure determination, lipid-binding analysis, comparison with bison NHA2 structure International Journal of Molecular Sciences High 40362458
2025 Brd4 (bromodomain protein 4) transcriptionally activates Slc9b2/NHA2 in osteoclasts. Brd4 conditional knockout reduced osteoclastogenesis and glycolysis; overexpression of Slc9b2 partially rescued the impaired osteoclastogenesis caused by Brd4 depletion, placing NHA2 as a downstream effector of Brd4 in osteoclast metabolism and differentiation. Conditional Brd4 KO mice (Lyz2-Cre and Ctsk-Cre), transcriptomic screening, Slc9b2 overexpression rescue experiment, bone mass and osteoclast activity assessment Clinical and Translational Medicine Medium 41115147
2026 Trafficking of human NHA2 to the plasma membrane requires cornichon COPII cargo receptors. Both yeast ScErv14 and human CNIH cornichons (CNIH1, CNIH2, CNIH4) improved plasma-membrane targeting and functioning of NHA2 expressed in S. cerevisiae, identifying NHA2 as a cargo of cornichon COPII cargo receptors and establishing a requirement for this ER-exit machinery in NHA2 surface delivery. Heterologous expression in S. cerevisiae with ERV14 replacement by human CNIHs, plasma-membrane targeting assay, functional complementation assay, AlphaFold3 modeling Protein Science Medium 41676957

Source papers

Stage 0 corpus · 20 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2013 Sodium/hydrogen exchanger NHA2 is critical for insulin secretion in β-cells. Proceedings of the National Academy of Sciences of the United States of America 52 23720317
2008 Characterization of the sodium/hydrogen exchanger NHA2. Journal of the American Society of Nephrology : JASN 51 18508966
2015 Transport proteins NHA1 and NHA2 are essential for survival, but have distinct transport modalities. Proceedings of the National Academy of Sciences of the United States of America 49 26324901
2007 NHA-oc/NHA2: a mitochondrial cation-proton antiporter selectively expressed in osteoclasts. Bone 39 17988971
2010 Sodium/hydrogen exchanger NHA2 in osteoclasts: subcellular localization and role in vitro and in vivo. Bone 31 20441802
2012 Unconventional chemiosmotic coupling of NHA2, a mammalian Na+/H+ antiporter, to a plasma membrane H+ gradient. The Journal of biological chemistry 30 22948142
2016 NHA2 is expressed in distal nephron and regulated by dietary sodium. Journal of physiology and biochemistry 17 27909897
2018 NHA2 promotes cyst development in an in vitro model of polycystic kidney disease. The Journal of physiology 14 30242840
2007 Expression analysis of nha-oc/NHA2: a novel gene selectively expressed in osteoclasts. Gene expression patterns : GEP 14 17698421
2020 The sodium/proton exchanger NHA2 regulates blood pressure through a WNK4-NCC dependent pathway in the kidney. Kidney international 13 32956652
2016 Loss of Sodium/Hydrogen Exchanger NHA2 Exacerbates Obesity- and Aging-Induced Glucose Intolerance in Mice. PloS one 11 27685945
2016 Evolution of Vertebrate Solute Carrier Family 9B Genes and Proteins (SLC9B): Evidence for a Marsupial Origin for Testis Specific SLC9B1 from an Ancestral Vertebrate SLC9B2 Gene. Journal of phylogenetics & evolutionary biology 10 28868326
2010 Mutational analysis of NHAoc/NHA2 in Saccharomyces cerevisiae. Biochimica et biophysica acta 8 20713131
2007 Production of Yarrowia lipolytica Nha2 Na+/H+ antiporter improves the salt tolerance of Saccharomyces cerevisiae. Folia microbiologica 6 18450222
2022 Allosteric links between the hydrophilic N-terminus and transmembrane core of human Na+ /H+ antiporter NHA2. Protein science : a publication of the Protein Society 5 36177733
2022 Physiological and Molecular Function of the Sodium/Hydrogen Exchanger NHA2 (SLC9B2). Chimia 3 38069797
2025 Structure and Inhibition of the Human Na+/H+ Exchanger SLC9B2. International journal of molecular sciences 1 40362458
2024 Residues R177 and S178 of the human Na+/H+ antiporter NHA2 are involved in its inhibition by the flavonoid phloretin. FEBS letters 1 39737617
2026 Trafficking of the human Na+/H+ antiporter NHA2 to the plasma membrane requires cornichon COPII cargo receptors. Protein science : a publication of the Protein Society 0 41676957
2025 Loss of Brd4 alleviates pathological bone loss via Slc9b2 suppression in osteoclastogenesis. Clinical and translational medicine 0 41115147

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