The acidic A-domain of Arabidopsis TOC159 occurs as a hyperphosphorylated protein.
The translocon at the outer membrane of the chloroplast assists the import of a large class of preproteins with amino-terminal transit sequences. The preprotein receptors Toc159 and Toc33 in Arabidopsis (Arabidopsis thaliana) are specific for the accumulation of abundant photosynthetic proteins. The receptors are homologous GTPases known to be regulated by phosphorylation within their GTP-binding domains. In addition to the central GTP-binding domain, Toc159 has an acidic N-terminal domain (A-domain) and a C-terminal membrane-anchoring domain (M-domain). The A-domain of Toc159 is dispensable for its in vivo activity in Arabidopsis and prone to degradation in pea (Pisum sativum). Therefore, it has been suggested to have a regulatory function. Here, we show that in Arabidopsis, the A-domain is not simply degraded but that it accumulates as a soluble, phosphorylated protein separated from Toc159. However, the physiological relevance of this process is unclear. The data show that the A-domain of Toc159 as well as those of its homologs Toc132 and Toc120 are targets of a casein kinase 2-like activity.
Agne
Birgit
B
Laboratoire de Physiologie Végétale, Université de Neuchâtel, CH-2009 Neuchatel, Switzerland.
Andrès
Charles
C
Montandon
Cyril
C
Christ
Bastien
B
Ertan
Anouk
A
Jung
Friederike
F
Infanger
Sibylle
S
Bischof
Sylvain
S
Baginsky
Sacha
S
Kessler
Felix
F
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism*; D047390:Casein Kinase II / Q000378:metabolism; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism; D002846:Chromatography, Affinity; D020558:GTP Phosphohydrolases / Q000737:chemistry* / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010748:Phosphopeptides / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D030821:Plants, Genetically Modified; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment; D013329:Structure-Activity Relationship; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism
D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D010748:Phosphopeptides; D011993:Recombinant Fusion Proteins; C403444:TOC159 protein, Arabidopsis; D006493:Heparin; D047390:Casein Kinase II; D020558:GTP Phosphohydrolases
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