title: Functional characterization of solute carrier (SLC) 26/sulfate permease (SulP) proteins in membrane mimetic systems.
abstract: Solute carrier (SLC) 26 or sulfate permease (SulP) anion transporters, belong to a phylogenetically ancient family of secondary active transporters. Members of the family are involved in several human genetic diseases and cell physiological processes. Despite their importance, the substrates for transport by this family of proteins have been poorly characterized. In this study, recombinant StmYchM/DauA, a SulP from Salmonella typhimurium was purified to homogeneity and functionally characterized. StmYchM/DauA was found to be a dimer in solution as determined by size exclusion chromatography coupled to multiple angle light scattering. We report a functional characterization of the SulP proteins in two membrane mimetic systems and reveal a dual nature of anionic substrates for SulP. StmYchM/DauA functionally incorporated into nanodiscs could bind fumarate with millimolar affinities (KD = 4.6 ± 0.29 mM) as detected by intrinsic tryptophan fluorescence quench studies. In contrast, electrophysiological experiments performed in reconstituted liposomes indicate a strong bicarbonate transport in the presence of chloride but no detectable electrogenic fumarate transport. We hence suggest that while SulP acts as an electrogenic bicarbonate transporter, fumarate may serve as substrate under different conditions indicating multiple functions of SulP.
authors.affiliation: Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max-von-Laue-Strasse 3, Frankfurt am Main, 60438, Germany. Electronic address: Lakshmi.Srinivasan@biophys.mpg.de.
authors.forename: Lakshmi
authors.initials: L
authors.lastname: Srinivasan
authors.affiliation: Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max-von-Laue-Strasse 3, Frankfurt am Main, 60438, Germany. Electronic address: Tonie.Baars@biophys.mpg.de.
authors.forename: Tonie Luise
authors.initials: TL
authors.lastname: Baars
authors.affiliation: Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max-von-Laue-Strasse 3, Frankfurt am Main 60438, Germany. Electronic address: Klaus.Fendler@biophys.mpg.de.
authors.forename: Klaus
authors.initials: K
authors.lastname: Fendler
authors.affiliation: Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max-von-Laue-Strasse 3, Frankfurt am Main, 60438, Germany. Electronic address: Hartmut.Michel@biophys.mpg.de.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Michel
mesh_terms: D027321:Anion Transport Proteins / Q000737:chemistry* / Q000302:isolation & purification; D001639:Bicarbonates / Q000737:chemistry; D001692:Biological Transport; D005650:Fumarates / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008566:Membranes / Q000737:chemistry* / Q000378:metabolism; D012486:Salmonella typhimurium / Q000737:chemistry / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D027321:Anion Transport Proteins; D001639:Bicarbonates; D005650:Fumarates; C022702:sulfate permease
keywords: Bicarbonate transport by sulfate permease; Fluorescence quench studies in nanodiscs; Membrane mimetics; Solid supported membrane-based electrophysiology; Solute carrier (SLC)26; Transport assays in proteoliposomes