The pore of plant K(+) channels is involved in voltage and pH sensing: domain-swapping between different K(+) channel alpha-subunits

• Published in: The Plant cell 2001-04, Vol.13 (4), p.943-952
• Main Authors: Hoth, S, Geiger, D, Becker, D, Hedrich, R
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Biosensing Techniques; Calcium - metabolism; Hydrogen-Ion Concentration; Molecular Sequence Data; Oocytes; Patch-Clamp Techniques; Plant Proteins - genetics; Plant Proteins - metabolism; Potassium Channels - genetics; Potassium Channels - metabolism; Potassium Channels, Inwardly Rectifying; Recombinant Fusion Proteins - metabolism; Sequence Alignment; Xenopus laevis
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.13.4.943

Plant K(+) uptake channel types differ with respect to their voltage, Ca(2)+, and pH dependence. Here, we constructed recombinant chimeric channels between KST1, a member of the inward-rectifying, acid-activated KAT1 family, and AKT3, a member of the weakly voltage-dependent, proton-blocked AKT2/3 family. The homologous pore regions of AKT3 (amino acids 216 to 287) and KST1 (amino acids 217 to 289) have been exchanged to generate the two chimeric channels AKT3/(p)KST1 and KST1/(p)AKT3. In contrast to AKT3 wild-type channels, AKT3/(p)KST1 revealed a strong inward rectification reminiscent of that of KST1. Correspondingly, the substitution of the KST1 by the AKT3 pore led to less pronounced rectification properties of KST1/(p)AKT3 compared with wild-type KST1. Besides the voltage dependence, the interaction between the chimera and extracellular H(+) and Ca(2)+ resembled the properties of the inserted rather than the respective wild-type pore. Whereas AKT3/(p)KST1 was acid activated and Ca(2)+ insensitive, extracellular protons and Ca(2)+ inhibited KST1/(p)AKT3. The regulation of the chimeric channels by cytoplasmic protons followed the respective wild-type backbone of the chimeric channels, indicating that the intracellular pH sensor is located outside the P domain. We thus conclude that essential elements for external pH and Ca(2)+ regulation and for the rectification of voltage-dependent K(+) uptake channels are located within the channel pore.