Engineered L-serine hydroxymethyltransferase from streptococcus thermophilus for the synthesis of α,α-dialkyl-α-amino acids

α,α-Disubstituted a-amino acids are central to biotechnological and biomedical chemical processes for their own sake and as substructures of biologically active molecules for diverse biomedical applications. Structurally, these compounds contain a quaternary stereocenter, which is particularly challenging for stereoselective synthesis. The pyridoxal-5′-phosphate (PLP)-dependent l -serine hydroxymethyltransferase from Streptococcus thermophilus (SHMT_Sth; EC 2.1.2.1) was engineered to achieve the stereoselective synthesis of a broad structural variety of α,α-dialkyl-α-amino acids. This was accomplished by the formation of quaternary stereocenters through aldol addition of the amino acids D-Ala and D-Ser to a wide acceptor scope catalyzed by the minimalist SHMT_Sth Y55T variant overcoming the limitation of the native enzyme for Gly. The SHMT_Sth Y55T variant tolerates aromatic and aliphatic aldehydes as well as hydroxy- and nitrogen-containing aldehydes as acceptors.