Computational investigation of the substrate recognition mechanism of protein d-aspartyl (l-isoaspartyl) O-methyltransferase by docking and molecular dynamics simulation studies and application to interpret size exclusion chromatography data

Unusual amino acid residues such as l-β-aspartyl (Asp), d-α-Asp, and d-β-Asp have been detected in proteins and peptides such as α-crystallin in the lens and β-amyloid in the brain. These residues increase with age, and hence they are associated with age-related diseases. The enzyme protein d-aspartyl (l-isoaspartyl) O-methyltransferase (PIMT) can revert these residues back to the normal l-α-Asp residue. PIMT catalyzes transmethylation of S-adenosylmethionine to l-β-Asp and d-α-Asp residues in proteins and peptides. In this work, the substrate recognition mechanism of PIMT was investigated using docking and molecular dynamics simulation studies. It was shown that the hydrogen bonds of Ser60 and Val214 to the carboxyl group of Asp are important components during substrate recognition by PIMT. In addition, specific hydrogen bonds were observed between the main chains of the substrates and those of Ala61 and Ile212 of PIMT when PIMT recognized l-β-Asp. Hydrophobic interactions between the (n − 1) residue of the substrates and Ile212 and Val214 of PIMT may also have an important effect on substrate binding. Volume changes upon substrate binding were also evaluated in the context of possible application to interpretation of size exclusion chromatography data.