A high-conductance solute channel in the chloroplastic outer envelope from Pea.
The pea chloroplastic outer envelope protein OEP24 can function as a general solute channel. OEP24 is present in chloroplasts, etioplasts, and non-green root plastids. The heterologously expressed protein forms a voltage-dependent, high-conductance (Lambda = 1.3 nS in 1 M KCl), and slightly cation-selective ion channel in reconstituted proteoliposomes. The highest open probability (P open approximately 0. 8) is at 0 mV, which is consistent with the absence of a transmembrane potential across the chloroplastic outer envelope. The OEP24 channels allow the flux of triosephosphate, dicarboxylic acids, positively or negatively charged amino acids, sugars, ATP, and Pi. Structure prediction algorithms and circular dichroism spectra indicate that OEP24 contains seven amphiphilic beta strands. The primary structure of OEP24 shows no homologies to mitochondrial or bacterial porins on a primary sequence basis, and OEP24 is functionally not inhibited by cadaverine, which is a potent inhibitor of bacterial porins. We conclude that OEP24 represents a new type of solute channel in the plastidic outer envelope.
Botanisches Institut, Universität Kiel, D-24098 Kiel, Germany.
K
K
Pohlmeyer
J
J
Soll
R
R
Grimm
K
K
Hill
R
R
Wagner
D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000502:physiology*; D002942:Circular Dichroism; D003001:Cloning, Molecular; D004926:Escherichia coli; D007425:Intracellular Membranes / Q000502:physiology*; D007473:Ion Channels / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D008051:Lipid Bilayers; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D018532:Pisum sativum / Q000378:metabolism*; D010940:Plant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D018087:Plastids / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism
D007473:Ion Channels; D008051:Lipid Bilayers; C113819:OEP24 protein, Pisum sativum; D010940:Plant Proteins; D011994:Recombinant Proteins