Protein methylation is one of the most important reversible post-translational modifications (PTMs). As a key regulator of numerous cellular processes, protein methylation is involved in almost all aspects of cell metabolism, development and differentiation (Chen et al., 2006). Protein methylation can occurr on either backbone or side-chain of several types of amino acid residues including lysine (K), arginine (R), proline (P), histidine (H), alanine (A), and asparagine (N) in the form of N-methylation (Bedford et al., 2005, Lee et al., 2005). Also, O-methylation of glutamic acids (E) and S-methylation of cysteine (C) and methionine (M) residues were also reported (Predel et al., 1999,