title: Phosphorylation regulates the assembly of chloroplast import machinery.
abstract: Chloroplast function depends on the translocation of cytosolically synthesized precursor proteins into the organelle. The recognition and transfer of most precursor proteins across the outer membrane depend on a membrane inserted complex. Two receptor components of this complex, Toc34 and Toc159, are GTPases, which can be phosphorylated by kinases present in the hosting membrane. However, the physiological function of phosphorylation is not yet understood in detail. It is demonstrated that both receptors are phosphorylated within their G-domains. In vitro, the phosphorylation of Toc34 disrupts both homo- and heterodimerization of the G-domains as determined using a phospho-mimicking mutant. In endogenous membranes this mutation or phosphorylation of the wild-type receptor disturbs the association of Toc34, but not of Toc159 with the translocation pore. Therefore, phosphorylation serves as an inhibitor for the association of Toc34 with other components of the complex and phosphorylation can now be discussed as a mechanism to exchange different isoforms of Toc34 within this ensemble.
authors.affiliation: JWGU Frankfurt am Main, Cluster of Excellence Macromolecular Complexes, Department of Biosciences, Max-von-Laue Str. 9, D-60439 Frankfurt, Germany.
authors.forename: Mislav
authors.initials: M
authors.lastname: Oreb
authors.forename: Anja
authors.initials: A
authors.lastname: Höfle
authors.forename: Oliver
authors.initials: O
authors.lastname: Mirus
authors.forename: Enrico
authors.initials: E
authors.lastname: Schleiff
mesh_terms: D017360:Arabidopsis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D019281:Dimerization; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport
chemical_list: D029681:Arabidopsis Proteins; D008565:Membrane Proteins; C403444:TOC159 protein, Arabidopsis; C491798:TOC34 protein, Arabidopsis; D020558:GTP Phosphohydrolases