Directed Evolution Toward Nonstandard Amino Acids by a Decarboxylative Aldol Reaction

Key words

whole-cell biocatalysis - decarboxylation - aldol reaction - amino acids - directed evolution

Significance

Buller and co-workers disclose an enantioselective synthesis of γ-hydroxy amino acids catalyzed by engineered variants of a pyridoxal 5′-phosphate (PLP)-dependent enzyme. Various products of C–C bond-forming reactions were obtained in moderate to excellent yields and enantio­selectivities. The optimized enzyme UstD^v2.0 is efficient in a whole-cell biocatalysis format, thereby eliminating the need for enzyme purification in gram-scale syntheses.

Comment

Unlike other classic aldolases, UstD is capable of decarboxylating the side chain of pyridoxal-bound l-aspartate to form a putative nucleophilic enamine intermediate, which renders the ­enantioselective C–C bond-forming reaction effectively irreversible. An X-ray crystal-structure ana­lysis of UstD^v2.0 revealed the active site and ­provides a foundation for probing the UstD ­mechanism. A broader scope of gram-scale whole-cell applications is anticipated.

Publication History

Article published online:
20 April 2022