protein-L-isoaspartate (D-aspartate) O-methyltransferase activity

Catalysis of the reaction: S-adenosyl-L-methionine + protein L-beta-aspartate = S-adenosyl-L-homocysteine + protein L-beta-aspartate methyl ester.

D-aspartyl/L-isoaspartyl methyltransferase activity, L-aspartyl/L-isoaspartyl protein methyltransferase activity, L-isoaspartyl protein carboxyl methyltransferase activity, L-isoaspartyl/D-aspartyl protein carboxyl methyltransferase activity, S-adenosyl-L-methionine:protein-L-isoaspartate O-methyltransferase activity, protein (D-aspartate) methyltransferase activity, protein D-aspartate methyltransferase activity, protein L-isoaspartate methyltransferase activity, protein L-isoaspartyl methyltransferase activity, protein O-methyltransferase (L-isoaspartate), protein beta-aspartate O-methyltransferase activity, protein-L-isoaspartate (D-aspartate) O-methyltransferase activity, protein-L-isoaspartate O-methyltransferase activity, protein-L-isoaspartate(D-aspartate) O-methyltransferase activity, protein-beta-aspartate O-methyltransferase activity