Characterization of Tic110, a channel-forming protein at the inner envelope membrane of chloroplasts, unveils a response to Ca(2+) and a stromal regulatory disulfide bridge.
Tic110 has been proposed to be a channel-forming protein at the inner envelope of chloroplasts whose function is essential for the import of proteins synthesized in the cytosol. Sequence features and topology determination experiments presently summarized suggest that Tic110 consists of six transmembrane helices. Its topology has been mapped by limited proteolysis experiments in combination with mass spectrometric determinations and cysteine modification analysis. Two hydrophobic transmembrane helices located in the N terminus serve as a signal for the localization of the protein to the membrane as shown previously. The other amphipathic transmembrane helices are located in the region composed of residues 92-959 in the pea sequence. This results in two regions in the intermembrane space localized to form supercomplexes with the TOC machinery and to receive the transit peptide of preproteins. A large region also resides in the stroma for interaction with proteins such as molecular chaperones. In addition to characterizing the topology of Tic110, we show that Ca(2+) has a dramatic effect on channel activity in vitro and that the protein has a redox-active disulfide with the potential to interact with stromal thioredoxin.
Balsera
Mónica
M
Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany; Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Grosshadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany. Electronic address: monica.balsera@psi.ch.
Goetze
Tom A
TA
Department of Biophysics, University of Osnabrück, Barbarastrasse 13 D-49076 Osnabrück, Germany.
Kovács-Bogdán
Erika
E
Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany; Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Grosshadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany.
Schürmann
Peter
P
Laboratorie de Biologie Moléculaire et Cellulaire, Université de Neuchâtel, Rue Emile-Argand 11, CH-2009 Neuchâtel, Switzerland.
Wagner
Richard
R
Department of Biophysics, University of Osnabrück, Barbarastrasse 13 D-49076 Osnabrück, Germany.
Buchanan
Bob B
BB
Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Grosshadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany; Department of Plant and Microbial Biology, University of California, Berkeley, California 94720.
Soll
Jürgen
J
Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany; Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Grosshadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany.
Bölter
Bettina
B
Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany; Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Grosshadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany.
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism*; D008969:Molecular Sequence Data; D018532:Pisum sativum / Q000378:metabolism*; D010449:Peptide Mapping; D010940:Plant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism
D004220:Disulfides; D010940:Plant Proteins; D011994:Recombinant Proteins; D003545:Cysteine; D002118:Calcium