Reference "Molecular basis of plant-specific acid activation of K+ uptake channels"

Reference ID

7698

Title

Molecular basis of plant-specific acid activation of K+ uptake channels

Source

Proceedings of the National Academy of Sciences of the United States of America, 1997, vol. 94, pp. 4806-4810

Authors (6)

Hoth-S	Dreyer-I
Dietrich-P	Becker-D
Muller-Rober-B	Hedrich-R

Abstract

During stomatal opening potassium uptake into guard cells and K+ channel
activation is tightly coupled to proton extrusion. The pH sensor of the K+
uptake channel in these motor cells has, however, not yet been identified.
Electrophysiological investigations on the voltage-gated, inward rectifying K+
channel in guard cell protoplasts from Solanum tuberosum (KST1), and the kst1
gene product expressed in Xenopus oocytes revealed that pH dependence is an
intrinsic property of the channel protein. Whereas extracellular acidification
resulted in a shift of the voltage-dependence toward less negative voltages, the
single-channel conductance was pH-insensitive. Mutational analysis allowed us to
relate this acid activation to both extracellular histidines in KST1. One
histidine is located within the linker between the transmembrane helices S3 and
S4 (H160), and the other within the putative pore-forming region P between S5
and S6 (H271). When both histidines were substituted by alanines the double
mutant completely lost its pH sensitivity. Among the single mutants, replacement
of the pore histidine, which is highly conserved in plant K+ channels, increased
or even inverted the pH sensitivity of KST1. From our molecular and biophysical
analyses we conclude that both extracellular sites are part of the pH sensor in
plant K+ uptake channels.