The preprotein conducting channel at the inner envelope membrane of plastids.
The preprotein translocation at the inner envelope membrane of chloroplasts so far involves five proteins: Tic110, Tic55, Tic40, Tic22 and Tic20. The molecular function of these proteins has not yet been established. Here, we demonstrate that Tic110 constitutes a central part of the preprotein translocation pore. Dependent on the presence of intact Tic110, radiolabelled preprotein specifically interacts with isolated inner envelope vesicles as well as with purified, recombinant Tic110 reconstituted into liposomes. Circular dichroism analysis reveals that Tic110 consists mainly of beta-sheets, a structure typically found in pore proteins. In planar lipid bilayers, recombinant Tic110 forms a cation-selective high-conductance channel with a calculated inner pore opening of 1.7 nm. Purified transit peptide causes strong flickering and a voltage-dependent block of the channel. Moreover, at the inner envelope membrane, a peptide-sensitive channel is described that shows properties basically identical to the channel formed by recombinant Tic110. We conclude that Tic110 has a distinct preprotein binding site and functions as a preprotein translocation pore at the inner envelope membrane.
Heins
Lisa
L
Botanisches Institut, Universität Kiel, Am Botanischen Garten 1-9, D-24118 Kiel, Germany.
Mehrle
Alexander
A
Hemmler
Roland
R
Wagner
Richard
R
Küchler
Michael
M
Hörmann
Friederike
F
Sveshnikov
Dmitry
D
Soll
Jürgen
J
D002736:Chloroplasts / Q000378:metabolism; D002942:Circular Dichroism; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation; D018532:Pisum sativum; D010455:Peptides / Q000737:chemistry; D018087:Plastids / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013997:Time Factors
D008081:Liposomes; D008565:Membrane Proteins; D010455:Peptides; D011994:Recombinant Proteins