SOS1
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SOS1 is the plasma membrane Na(+)/H(+) antiporter of Arabidopsis thaliana. It is responsible for the removal of intracellular sodium in exchange for an extracellular proton. SOS1 is composed of 1146 amino acids. Approximately 450 make the... more
SOS1 is the plasma membrane Na(+)/H(+) antiporter of Arabidopsis thaliana. It is responsible for the removal of intracellular sodium in exchange for an extracellular proton. SOS1 is composed of 1146 amino acids. Approximately 450 make the membrane domain, while the protein contains and a very large regulatory cytosolic domain of about 696 amino acids. Schizosaccharomyces pombe contains the salt tolerance Na(+)/H(+) antiporter proteins sod2. We examined the ability of SOS1 to rescue salt tolerance in S. pombe with a knockout of the sod2 gene (sod2::ura4). In addition, we characterized the importance of the regulatory tail of SOS1, in expression of the protein in S. pombe. We expressed full-length SOS1 and SOS1 shortened at the C-terminus and ending at amino acids 766 (medium) and 481 (short). The short version of SOS1 conveyed salt tolerance to sod2::ura4 yeast and Western blotting revealed that the protein was present. The protein was also targeted to the plasma membrane. The medium and full-length SOS1 protein were partially degraded and were not as well expressed as the short version of SOS1. The SOS1 short protein was also able to reduce Na(+) content in S. pombe. The full-length SOS1 dimerized and depended on the presence of the cytosolic tail. An analysis of SOS1 predicted a topology of 13 transmembrane segments, distinct from E. coli NhaA but similar to the Na(+)/H(+) exchangers Methanocaldococcus jannaschii NhaP1 and Thermus thermophile NapA
The plant plasma membrane Na+/H+ antiporter SOS1 (Salt Overlay Sensitive 1) of Arabidopsis thaliana is the major transporter extruding Na+ out of cells in exchange for an intracellular H+. The sodium extrusion process maintains a low... more
The plant plasma membrane Na+/H+ antiporter SOS1 (Salt Overlay Sensitive 1) of Arabidopsis thaliana is the major transporter extruding Na+ out of cells in exchange for an intracellular H+. The sodium extrusion process maintains a low intracellular Na+ concentration and thereby facilitates salt tolerance. A. thaliana SOS1 consists of 1146 amino acids, with the first 450 in a N-terminal membrane transport domain and the balance forming a cytosolic regulatory domain. For studies on characterization of the protein, two different constructs of SOS1 comprising of the residues 28 to 460 and 28 to 990 were cloned and overexpressed in methylotropic yeast strain of Pichia pastoris with a C-terminal histidine tag using the expression vector pPICZA. Styrene malic acid copolymers (SMA) were used as a cost-effective alternative to detergent for solubilization and isolation of this membrane protein. Immobilized Ni2+-ion affinity chromatography was used to purify the expressed protein resulting in a yield of ~0.6-2 mg of SOS1 per liter of Pichia pastoris culture. The SMA purified protein containing amino acids 28 to 990 was directly reconstituted into liposomes for determination of Na+ transport activity and was functionally active. However, similar reconstitution with amino acids 28-460 did not yield a functional protein. Other results have shown that the truncated SOS1 protein at amino acid 481 is active, which infers the presence of an element between residues 461-481 which is necessary for SOS1 activity. This region contains several conserved segments that may be important in SOS1 structure and function.