title: PSD-95 interacts with NBCn1 and enhances channel-like activity without affecting Na/HCO(3) cotransport.
abstract: OBJECTIVE
  The sodium/bicarbonate transporter NBCn1 plays an essential role in intracellular pH regulation and transepithelial HCO(3)(-) movement in the body. NBCn1 also has sodium channel-like activity uncoupled to Na/HCO(3) cotransport. We previously reported that NBCn1 interacts with the postsynaptic density protein PSD-95 in the brain. Here, we elucidated the structural determinant and functional consequence of NBCn1/PSD-95 interaction.
  
  
  METHODS
  
  
  
  RESULTS
  In rat hippocampal CA3 neurons, NBCn1 was localized to the postsynaptic membranes of both dendritic shafts and spines and occasionally to the presynaptic membranes. A GST/NBCn1 fusion protein containing the C-terminal 131 amino acids of NBCn1 pulled down PSD-95 from rat brain lysates, whereas GST/NBCn1-ΔETSL (deletion of the last four amino acids) and GST/NBCn2 (NCBE) lacking the same ETSL did not. NBCn1 and PSD-95 were coimmunoprecipitated in HEK 293 cells, and their interaction did not affect the efficacy of PSD-95 to bind to the NMDA receptor NR2A. PSD-95 has negligible effects on intracellular pH changes mediated by NBCn1 in HEK 293 cells and Xenopus oocytes. However, PSD-95 increased an ionic conductance produced by NBCn1 channel-like activity. This increase was abolished by NBCn1-ΔETSL or by the peptide containing the last 15 amino acids of NBCn1.
  
  
  CONCLUSIONS
  Our data suggest that PSD-95 interacts with NBCn1 and increases its channel-like activity while negligibly affecting Na/HCO(3) cotransport. The possibility that the channel-like activity occurs via an intermolecular cavity of multimeric NBCn1 proteins is discussed.
authors.affiliation: Department of Physiology, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: Soojung
authors.initials: S
authors.lastname: Lee
authors.forename: Han Soo
authors.initials: HS
authors.lastname: Yang
authors.forename: Eunjin
authors.initials: E
authors.lastname: Kim
authors.forename: Eun Ji
authors.initials: EJ
authors.lastname: Ju
authors.forename: Min Hyung
authors.initials: MH
authors.lastname: Kwon
authors.forename: R Kyle
authors.initials: RK
authors.lastname: Dudley
authors.forename: Yoland
authors.initials: Y
authors.lastname: Smith
authors.forename: C Chris
authors.initials: CC
authors.lastname: Yun
authors.forename: Inyeong
authors.initials: I
authors.lastname: Choi
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D056654:CA3 Region, Hippocampal / Q000166:cytology; D049229:Dendritic Spines / Q000378:metabolism; D000076122:Disks Large Homolog 4 Protein; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D054731:PDZ Domains; D010446:Peptide Fragments / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D017693:Sodium Bicarbonate / Q000378:metabolism*; D027982:Sodium-Bicarbonate Symporters / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism; D014981:Xenopus
chemical_list: D000076122:Disks Large Homolog 4 Protein; C501449:Dlg4 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D010446:Peptide Fragments; C498902:Slc4a7 protein, rat; D027982:Sodium-Bicarbonate Symporters; D017693:Sodium Bicarbonate