Rational engineering of esterases for improved amidase specificity in amide synthesis and hydrolysis

Sammanfattning: Biocatalysis is an ever evolving field that uses enzymes or microorganisms for chemical synthesis. By utilizing enzymes that generally have evolved for specific reactions under mild conditions and temperatures, biocatalysis can be a more environmentally friendly option compared to traditional chemistry.Amide-type chemistries are important and bond formation avoiding poor atom economy is of high priority in organic chemistry. Biocatalysis could potentially be a solution but restricted substrate scope is a limitation. Esterases/lipases usually display broad substrate scope and catalytic promiscuity but are poor at hydrolyzing amides compared to amidases/proteases. The difference between the two enzyme classes is hypothesized to reside in one key hydrogen bond present in amidases, which facilitates the transition state for nitrogen inversion during catalysis.In this thesis the work has been focused on introducing a stabilizing hydrogen bond acceptor in esterases, mimicking that found in amidases, to develop better enzymatic catalysts for amide-based chemistries.By two strategies, side-chain or water interaction, variants were created in three esterases that displayed up to 210-times increased relative amidase specificity compared to the wild type. The best variant displayed reduced activation enthalpy corresponding to a weak hydrogen bond. The results show an estimated lower limit on how much the hydrogen bond can be worth to catalysis.MsAcT catalyze kinetically controlled N-acylations in water. An enzymatic one-pot one-step cascade was developed for the formation of amides from aldehydes in water that gave 97% conversion. In addition, engineered variants of MsAcT with increased substrate scope could synthesize an amide in water with 81% conversion, where the wild type gave no conversion. Moreover, variants of MsAcT displayed up to 32-fold change in specificity towards amide synthesis and a switch in reaction preference favoring amide over ester synthesis.