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Post-translational modifications of arabinogalactan-peptides of Arabidopsis thaliana. Endoplasmic reticulum and glycosylphosphatidylinositol-anchor signal cleavage sites and hydroxylation of proline.

Authors
  • Schultz, Carolyn J
  • Ferguson, Kris L
  • Lahnstein, Jelle
  • Bacic, Antony
Type
Published Article
Journal
The Journal of biological chemistry
Publication Date
Oct 29, 2004
Volume
279
Issue
44
Pages
45503–45511
Identifiers
PMID: 15322080
Source
Medline
License
Unknown

Abstract

We have developed a method for separating the deglycosylated protein/peptide backbones of the small arabinogalactan (AG)-peptides from the larger classical arabinogalactan-proteins (AGPs). AGPs are an important class of plant proteoglycans implicated in plant growth and development. Separation of AG-peptides enabled us to identify eight of 12 AG-peptides from Arabidopsis thaliana predicted from genomic sequences. Of the remaining four, two have low abundance based on expressed sequence tag databases and the other two are only present in pollen (At3g20865) or flowers (At3g57690) and therefore would not be detected in our analysis. Characterization of AG-peptides was performed using matrix-assisted laser desorption ionization-time of flight mass spectrometry and tandem mass spectrometry protein sequencing. These data provide (i) experimental evidence that AG-peptides are processed in vivo for the addition of a glycosylphosphatidylinositol (GPI) anchor, (ii) cleavage site information for both the endoplasmic reticulum secretion signal and the GPI-anchor signal for eight of the 12 AG-peptides, and (iii) experimental evidence that the Gly-Pro motif is hydroxylated in vivo. Furthermore, we show that AtAGP16 is GPI-anchored despite its unusually long hydrophobic C-terminal GPI-signal sequence. Prior to this work, the GPI-anchor cleavage site for only two plant proteins, NaAGP1 from Nicotiana alata and PcAGP1 from Pyrus communis, had been determined experimentally. Characterization of the post-translational modifications of AG-peptides contributes toward obtaining the complete primary structure of this class of biologically important plant proteoglycans and provides a greater understanding of post-translational modifications of plant proteins.

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