Asymmetric synthesis of cis-3,5-diacetoxycyclopent-1-ene using metagenome-derived hydrolases

Sequence-Based Prediction of Promiscuous Acyltransferase Activity in Hydrolases

Certain hydrolases preferentially catalyze acyl transfer over hydrolysis in an aqueous environment. However, the molecular and structural reasons for this phenomenon are still unclear. Herein, we provide evidence that acyltransferase activity in esterases highly correlates with the hydrophobicity of the substrate-binding pocket. A hydrophobicity scoring system developed in this work allows accurate prediction of promiscuous acyltransferase activity solely from the amino acid sequence of the cap domain. This concept was experimentally verified by systematic investigation of several homologous esterases, leading to the discovery of five novel promiscuous acyltransferases. We also developed a simple yet versatile colorimetric assay for rapid characterization of novel acyltransferases. This study demonstrates that promiscuous acyltransferase activity is not as rare as previously thought and provides access to a vast number of novel acyltransferases with diverse substrate specificity and potential applications.

A Novel High-Throughput Assay Enables the Direct Identification of Acyltransferases

Acyltransferases are enzymes that are capable of catalyzing the transesterification of non-activated esters in an aqueous environment and therefore represent interesting catalysts for applications in various fields. However, only a few acyltransferases have been identified so far, which can be explained by the lack of a simple, broadly applicable high-throughput assay for the identification of these enzymes from large libraries. Here, we present the development of such an assay that is based on the enzymatic formation of oligocarbonates from dimethyl carbonate and 1,6-hexanediol. In contrast to the monomers used as substrates, the oligomers are not soluble in the aqueous environment and form a precipitate which is used to detect enzyme activity by the naked eye, by absorbance or by fluorescence measurements. With activity detected and thus confirmed for the enzymes Est8 and MsAcT, the assay enabled the first identification of acyltransferases that act on carbonates. It will thus allow for the discovery of further efficient acyltransferases or of more efficient variants via enzyme engineering.

Enantioselective kinetic resolution of phenylalkyl carboxylic acids using metagenome-derived esterases

Enantiomerically pure β-arylalkyl carboxylic acids are important synthetic intermediates for the preparation of a wide range of compounds with biological and pharmacological activities. A library of 83 enzymes isolated from the metagenome was searched for activity in the hydrolysis of ethyl esters of three racemic phenylalkyl carboxylic acids by a microtiter plate-based screening using a pH-indicator assay. Out of these, 20 enzymes were found to be active and were subjected to analytical scale biocatalysis in order to determine their enantioselectivity. The most enantioselective and also enantiocomplementary biocatalysts were then used for preparative scale reactions. Thus, both enantiomers of each of the three phenylalkyl carboxylic acids studied could be obtained in excellent optical purity and high yields.