Rapidly and Precisely Cross-Linked Enzymes Using Bio-Orthogonal Chemistry from Cell Lysate for the Synthesis of (S)-1-(2,6-Dichloro-3-fluorophenyl) Ethanol

To develop a method for preparing rapidly, precisely, and bio-orthogonally cross-linked enzymes (RP-CLEs), nonstandard amino acids (NSAAs) were inserted into the enzyme protein, and microwave irradiation was used to accelerate its site-specific linkage through Cu-free strain-promoted alkyne–azide cycloaddition (SPAAC). To this end, we selected aldehyde ketone reductase (AKR) as model enzyme, and AKR mutants were obtained by five-point insertion of p-azido-l-phenylalanine (pAzF) which were subsequently cross-linked to form RP-CLEs from cell lysate supernatant under microwave irradiation. The AKR five-point mutant and corresponding RP-CLEs were characterized using MALDI-TOF MS, SEM, and FT-IR, respectively. The specific activities of RP-CLEs of three-point and five-point AKR were 1.27 and 2.06 U·mg–1, 1.21- and 2.16-fold those of the corresponding free enzymes, respectively. In the asymmetric synthesis of (S)-1-(2,6-dichloro-3-fluorophenyl) ethanol, the yield was up to 90.8%, and the ee was 99.98%. Moreover, after 6 consecutive 12 h reaction cycles, AKR five-point RP-CLEs still retained 80% of their initial activity. Thus, depending on the enzyme structure analysis, different numbers of NSAAs could be reasonably incorporated into the protein to accurately guide and control the covalent linkage to form RP-CLEs. This green method could be further developed both to generate bio-orthogonally cross-linked enzyme and separate them from nontarget proteins for industrial biocatalysis.