Murine Elongation Factor 1α (EF-1α) Is Posttranslationally Modified by Novel Amide-linked Ethanolamine-phosphoglycerol Moieties: Addition of Ethanolamine-phosphoglycerol to Specific Glutamic Acid Residues on EF-1α

Abstract

Elongation Factor 1α (EF-1α), an important eukaryotic translation factor, transports charged aminoacyl-tRNA from the cytosol to the ribosomes during poly-peptide synthesis. Metabolic radiolabeling with [3H] ethanolamine shows that, in all cells examined, EF-1α is the major radiolabeled protein. Radiolabeled EF-1α has an apparent Mr = 53,000 and a basic isoelectric point. It is cytosolic and does not contain N-linked oligosaccharides. Trypsin digestion of murine EF-1α generated two major [3H]ethanolamine-labeled peptides. Three peptides were sequenced and were identical to two distinct regions of the human EF-1α protein. Blank sequencing cycles coinciding with glutamic acid in the human cDNA-derived sequence were also found to release [3H]ethanolamine, and compositional analysis of these peptides confirmed the presence of glutamic acid. Dansylation analysis demonstrates that the amine group of the ethanolamine is blocked. These results indicate that EF-1α is posttranslationally modified by the covalent attachment of ethanolamine via an amide bond to at least two specific glutamic acid residues (Glu-301 and Glu-374). The hydroxyl group of the attached ethanolamine was shown by mass spectrometry and compositional analysis, to be further modified by the addition of a phosphoglycerol unit. This novel posttranslational modification may represent an important alteration of EF-1α, comparable to the regulatory effects of posttranslational methylation of EF-1α lysine residues.