Figure 1.

Classification and structure of HKT1 proteins. (A) Structural analysis of HKT1 protein containing Ser or Gly residues in their conserved regions. Members of class-1 transporters carry a Ser in the selectivity filter position while on the same position class-2 transporters contain a Gly residue. P denotes pore-loop domain while N and C indicate N-terminus and C-terminus of HKT-proteins. (B) Members of class-1 HKT1 that carry a Ser residue transport Na⁺ while members of class-2 that carry a Gly residue can transport both Na⁺ as well as K⁺