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Solute carrier (SLC)26; Bicarbonate transport by sulfate permease; Membrane mimetics; Fluorescence quench studies in nanodiscs; Solid supported membrane-based; electrophysiology; Transport assays in proteoliposomes
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 SulPfromSalmonella typhimurium was purified to homogeneity and functionally characterized. StmYchM/DauAwas found to be a dimer in solution as determined by size exclusion chromatography coupled tomultiple 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±0.29mM) 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.
