title: Syntaxin 1A has a specific binding site in the H3 domain that is critical for targeting of H+-ATPase to apical membrane of renal epithelial cells.
abstract: H(+) transport in the collecting duct is regulated by exocytic insertion of H(+)-ATPase-laden vesicles into the apical membrane. The soluble N-ethylmaleimide-sensitive fusion protein attachment protein (SNAP) receptor (SNARE) proteins are critical for exocytosis. Syntaxin 1A contains three main domains, SNARE N, H3, and carboxy-terminal transmembrane domain. Several syntaxin isoforms form SNARE fusion complexes through the H3 domain; only syntaxin 1A, through its H3 domain, also binds H(+)-ATPase. This raised the possibility that there are separate binding sites within the H3 domain of syntaxin 1A for H(+)-ATPase and for SNARE proteins. A series of truncations in the H3 domain of syntaxin 1A were made and expressed as glutathione S-transferase (GST) fusion proteins. We determined the amount of H(+)-ATPase and SNARE proteins in rat kidney homogenate that complexed with GST-syntaxin molecules. Full-length syntaxin isoforms and syntaxin-1ADeltaC [amino acids (aa) 1-264] formed complexes with H(+)-ATPase and SNAP23 and vesicle-associated membrane polypeptide (VAMP). A cassette within the H3 portion was found that bound H(+)-ATPase (aa 235-264) and another that bound SNAP23 and VAMP (aa 190-234) to an equivalent degree as full-length syntaxin. However, the aa 235-264 cassette alone without the SNARE N (aa 1-160) does not bind but requires ligation to the SNARE N to bind H(+)-ATPase. When this chimerical construct was transected into inner medullary collecting duct cells it inhibited intracellular pH recovery, an index of H(+)-ATPase mediated secretion. We conclude that within the H3 domain of syntaxin 1A is a unique cassette that participates in the binding of the H(+)-ATPase to the apical membrane and confers specificity of syntaxin 1A in the process of H(+)-ATPase exocytosis.
authors.affiliation: Renal Section, Boston University Medical Center, Massachusetts, USA.
authors.forename: Guangmu
authors.initials: G
authors.lastname: Li
authors.forename: Qiongqiong
authors.initials: Q
authors.lastname: Yang
authors.forename: Edward A
authors.initials: EA
authors.lastname: Alexander
authors.forename: John H
authors.initials: JH
authors.lastname: Schwartz
mesh_terms: D000818:Animals; D000954:Antigens, Surface / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D016764:Cell Polarity / Q000502:physiology*; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology; D015870:Gene Expression; D007668:Kidney / Q000166:cytology*; D008565:Membrane Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D050683:R-SNARE Proteins; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050827:Syntaxin 1
chemical_list: D000954:Antigens, Surface; D002352:Carrier Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D050683:R-SNARE Proteins; D011993:Recombinant Fusion Proteins; C100493:SNAP23 protein, human; C494212:STX1A protein, human; C494213:Stx1a protein, rat; D050827:Syntaxin 1; D006180:Proton-Translocating ATPases