The chloroplast protein import channel Toc75: pore properties and interaction with transit peptides.
The channel properties of Toc75 (the protein import pore of the outer chloroplastic membrane) were further characterized by electrophysiological measurements in planar lipid bilayers. After improvement of the Toc75 reconstitution procedure the voltage dependence of the channel open probability resembled those observed for other beta-barrel pores. Studies concerning the pore size of the reconstituted Toc75 indicate the presence of a narrow restriction zone corresponding to the selectivity filter and a wider pore vestibule with diameters of approximately 14 A and 26 A, respectively. Interactions between Toc75 and different peptides (a genuine chloroplastic transit peptide, a synthetic peptide resembling a transit peptide, and a mitochondrial presequence) show that Toc75 itself is able to differentiate between these peptides and the recognition is based on both conformational and electrostatic interactions.
Fachbereich Biologie/Chemie, Universität Osnabrück, D-49034 Osnabrück, Germany.
Silke C
SC
Hinnah
Richard
R
Wagner
Natalia
N
Sveshnikova
Roswitha
R
Harrer
Jürgen
J
Soll
D000595:Amino Acid Sequence; D055592:Biophysical Phenomena; D001703:Biophysics; D002736:Chloroplasts / Q000378:metabolism*; D004594:Electrophysiology; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D017830:Octoxynol / Q000494:pharmacology; D010455:Peptides / Q000737:chemistry; D010940:Plant Proteins; D011092:Polyethylene Glycols / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D011498:Protein Precursors / Q000737:chemistry* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D014867:Water
D008051:Lipid Bilayers; D008565:Membrane Proteins; C103933:OEP75 protein precursor, plant; D010455:Peptides; D010940:Plant Proteins; D011498:Protein Precursors; D014867:Water; D011092:Polyethylene Glycols; D017830:Octoxynol