Protein L-Isoaspartate O-Methyltransferase (PCMT1): A Key Player of Spontaneously Arisen Protein Damage Repair

Methylation of aspartic acid residues was first described in the literature in erythrocytes as a possible step of repairing aged membrane proteins [1]. During the process of aging, L-aspartyl residues are spontaneously converted to L-isoaspartyl via the unstable intermediate L-succinimide which undergoes a spontaneous hydrolysis, generating a mixture of normal L-aspartate (15-30%) and abnormal L-isoaspartate (7085%), pointed out as steps 2 and 3 in Figure 1 respectively [2]. Accumulation of this abnormal form of aspartate is recognized as damage in the cell and therefore needs to be repaired [3].