Molecular properties of Oep21, an ATP-regulated anion-selective solute channel from the outer chloroplast membrane.
The flux of phosphorylated carbohydrates, the major export products of chloroplasts, is regulated at the level of the inner and presumably also at the level of the outer membrane. This is achieved through modulation of the outer membrane Oep21 channel currents and tuning of its ion selectivity. Refined analysis of the Oep21 channel properties by biochemical and electrophysiological methods revealed a channel formed by eight beta-strands with a wider pore vestibule of dvest approximately 2.4 nm at the intermembrane site and a narrower filter pore of drestr approximately 1 nm. The Oep21 pore contains two high affinity sites for ATP, one located at a relative transmembrane electrical distance delta = 0.56 and the second close to the vestibule at the intermembrane site. The ATP-dependent current block and reduction in anion selectivity of the Oep21 channel is relieved by the competitive binding of phosphorylated metabolic intermediates like 3-phosphoglycerate and glycerinaldehyde 3-phosphate. Deletion of a C-terminal putative FX4K binding motif in Oep21 decreased the capability of the channel to tune its ion selectivity by about 50%, whereas current block remained unchanged.
Hemmler
Roland
R
Biophysik, Universität Osnabrück, FB Biologie/Chemie, Barbarastrasse 11, D-49034 Osnabrück, Germany.
Becker
Thomas
T
Schleiff
Enrico
E
Bölter
Bettina
B
Stahl
Tanja
T
Soll
Jürgen
J
Götze
Tom A
TA
Braams
Simona
S
Wagner
Richard
R
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000838:Anions / Q000378:metabolism*; D001667:Binding, Competitive; D002736:Chloroplasts / Q000378:metabolism*; D017353:Gene Deletion; D005986:Glyceraldehyde 3-Phosphate / Q000378:metabolism; D005988:Glyceric Acids / Q000378:metabolism; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism*; D007473:Ion Channels / Q000502:physiology*; D008051:Lipid Bilayers; D008564:Membrane Potentials; D018532:Pisum sativum / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D010940:Plant Proteins / Q000378:metabolism*
D000838:Anions; D005988:Glyceric Acids; D007473:Ion Channels; D008051:Lipid Bilayers; D010940:Plant Proteins; D005986:Glyceraldehyde 3-Phosphate; C005156:3-phosphoglycerate; D000255:Adenosine Triphosphate