Abstract
Sodium dependent neutral amino acid transporter (SNAT) 2, a member of the solute carrier (SLC) 38 family, system A, mediates the coupled transport of sodium and small neutral amino acids across a cell's membrane. There has been proposed structural homology between SNAT2 and the sodium/betaine symporter, BetP. We mutated two conserved amino acids that have been shown to be ligands involved in BetP sodium binding: serine-225 and methionine-229. Both residues are found in the predicted TMD 5. The functional consequences of the S225A mutation are a slight reduction in the apparent affinity for alanine, and a dramatic reduction of the apparent sodium affinity. M229A also shows a reduced apparent affinity for alanine. These results demonstrate there is involvement of these residues in the sodium coordination and/or amino acid interaction with SNAT2. It also shows the involvement of TMD 5, which previously had not been thought to be involved with sodium binding in SNAT2.
Published Version
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