Discovery and Design of Family VIII Carboxylesterases as Highly Efficient Acyltransferases

Promiscuous acyltransferase activity is the ability of certain hydrolases to preferentially catalyze acyl transfer over hydrolysis, even in bulk water. However, poor enantioselectivity, low transfer efficiency, significant product hydrolysis, and limited substrate scope represent considerable drawbacks for their application. By activity-based screening of several hydrolases, we identified the family VIII carboxylesterase, EstCE1, as an unprecedentedly efficient acyltransferase. EstCE1 catalyzes the irreversible amidation and carbamoylation of amines in water, which enabled the synthesis of the drug moclobemide from methyl 4-chlorobenzoate and 4-(2-aminoethyl)morpholine (ca. 20 % conversion). We solved the crystal structure of EstCE1 and detailed structure-function analysis revealed a three-amino acid motif important for promiscuous acyltransferase activity. Introducing this motif into an esterase without acetyltransferase activity transformed a hydrolase into an acyltransferase.

Automated summary

EstCE1, identified as an efficient acyltransferase catalyzing amidation and carbamoylation in water, provides a solution to the current challenges faced by promiscuous enzymes in application. The structure-function analysis of EstCE1 reveals a three-amino acid motif essential for its promiscuous acyltransferase activity. Introducing this motif into an esterase without acetyltransferase activity can transform it into an acyltransferase.