From global phosphoproteomics to individual proteins: the case of translation elongation factor eEF1A.

Phosphoproteomics is often aimed at deciphering the modified components of signaling pathways in certain organisms, tissues and pathologies. Phosphorylation of housekeeping proteins, albeit important, usually attracts less attention. Here, we provide targeted analysis of eukaryotic translation elongation factor 1A (eEF1A), which is the main element of peptide elongation machinery. There are 97% homologous A1 and A2 isoforms of eEF1A; their expression in mammalian tissues is mutually exclusive and differentially regulated in development. The A2 isoform reveals proto-oncogenic properties and specifically interacts with some cellular proteins. Several tyrosine residues shown experimentally to be phosphorylated in eEF1A1 are hardly solution accessible, so their phosphorylation could be linked with structural rearrangement of the protein molecule. The possible role of tyrosine phosphorylation in providing the background for structural differences between the 'extended' A1 isoform and the compact oncogenic A2 isoform is discussed. The 'road map' for targeted analysis of any protein of interest using phosphoproteomics data is presented.