Journal: Science Advances
Article Title: Phosphorylation at serine-260 of Toc33 is essential for chloroplast biogenesis
doi: 10.1126/sciadv.adu4054
Figure Lengend Snippet: ( A ) Purified protein for in vitro kinase assay. Flag-Toc33 lacking the transmembrane domain (ΔTM), Flag-CTR1 kinase domain (KD), and the inactive Flag-CTR1 kinase domain mutant (Flag-CTR1-KD D694E ) were purified from E. coli . ( B ) In vitro kinase assay using 32 P[γATP] radiolabeling. ( C to E ) GFP-Toc33 phosphorylation and abundance correspond to increasing Myc-CTR1 coexpression in protoplasts from (C) WT, (D) etr1-1 , and (E) ein2-5 . Protein samples were separated by SDS-PAGE with and without Phos-tag. ( F ) A phosphopeptide spectrum from tandem mass spectrometry (MS/MS) identifying Ser260 as a Toc33 phosphorylation site by CTR1. The mass shift between y5 and y6 (69 Da) confirms S260 phosphorylation (Ser mass 87 Da + phosphate 80 Da − neutral loss H 3 PO 4 98 Da = 69 Da). ( G ) Phosphorylation of Myc-Toc33-WT, Myc-Toc33-S258A, or Myc-Toc33-S260A mutant proteins by GFP-CTR1 in Arabidopsis protoplasts, analyzed via SDS-PAGE with and without Phos-tag.
Article Snippet: The samples were desalted using a Pierce C18 spin column (Thermo Fisher Scientific) and phosphoenriched using the Spin-Tip PolyMAC-Ti Phosphopeptide Enrichment Kit (Tymora) following the manufacturer’s protocol.
Techniques: Purification, In Vitro, Kinase Assay, Mutagenesis, Radioactivity, SDS Page, Mass Spectrometry, Tandem Mass Spectroscopy