title: Toc64, a new component of the protein translocon of chloroplasts.
abstract: A subunit of the preprotein translocon of the outer envelope of chloroplasts (Toc complex) of 64 kD is described, Toc64. Toc64 copurifies on sucrose density gradients with the isolated Toc complex. Furthermore, it can be cross-linked in intact chloroplasts to a high molecular weight complex containing both Toc and Tic subunits and a precursor protein. The 0 A cross-linker CuCl(2) yields the reversible formation of disulfide bridge(s) between Toc64 and the established Toc complex subunits in purified outer envelope membranes. Toc64 contains three tetratricopeptide repeat motifs that are exposed at the chloroplast cytosol interface. We propose that Toc64 functions early in preprotein translocation, maybe as a docking protein for cytosolic cofactors of the protein import into chloroplasts.
authors.affiliation: Botanisches Institut, Christian-Albrechts-Universität Kiel, D-24118 Kiel, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Sohrt
authors.forename: J
authors.initials: J
authors.lastname: Soll
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002736:Chloroplasts / Q000737:chemistry* / Q000378:metabolism; D003001:Cloning, Molecular; D003300:Copper; D003432:Cross-Linking Reagents; D004220:Disulfides / Q000032:analysis; D007425:Intracellular Membranes / Q000737:chemistry* / Q000378:metabolism; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D018532:Pisum sativum; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D014176:Protein Biosynthesis; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014908:Triticum / Q000378:metabolism
chemical_list: D003432:Cross-Linking Reagents; D004220:Disulfides; D046911:Macromolecular Substances; D008565:Membrane Proteins; D010940:Plant Proteins; D011994:Recombinant Proteins; C406816:Toc64 protein, Pisum sativum; D003300:Copper; C029892:cupric chloride