One goal of our project is to understand the mechanism by which elongation factor 1A (eEF-1A) regulates phosphatidylinositol 4-kinase activity. eEF-1A is a multifunctional protein. There are three known posttranslational modifications of eEF-1A which could potentially affect its function. Except for phosphorylation, the other posttranslational modifications have not been demonstrated in plants. We used MALDI-MS to show that carrot eEF-1A contains a phosphoglycerylethanolamine (PGE) posttranslational modification and to identify the peptide fragment which is modified. While we could demonstrate by in vivo labeling studies that eEF-1A incorporated [14C]ethanolamine it was only by using mass spectrometry that we could definitely characterize the postranslational modification. Our data indicate that the PGE posttranslational modification alone does not affect the function of eEF-1A; however, in combination with other posttranslational modifications, the PGE lipid modification could affect the distribution and thereby affect the function of eEF-1A within the cell. We are continuing our studies using site-directed mutagenesis to knock out the posttranslationally modified amino acid. The mass spectra data were essential for this work.
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