Substrate recognition component of an ECS (Elongin BC-CUL5- SOCS-box protein) E3 ubiquitin ligase complex which mediates the ubiquitination and subsequent proteasomal degradation of target proteins (PubMed:35486881). Specifically binds to the methyltransferase cofactor S-adenosylmethionine (AdoMet) via the N-terminal AdoMet binding motif, but does not display methyltransferase activity (PubMed:35486881). May provide an alternate maintenance pathway for modified proteins by acting as a damage-specific E3 ubiquitin ligase adaptor protein (PubMed:35486881). . This is the function of ENSG00000168300 (PCMTD1, protein-L-isoaspartate (D-aspartate) O-methyltransferase domain containing 1).