Highly Enantioselective Biohydrolysis ofsec-Alkyl Sulfate Esters with Inversion of Configuration Catalysed byPseudomonas spp

Colorimetric Determination of Sulfate via an Enzyme Cascade for High-Throughput Detection of Sulfatase Activity

High-throughput screening (HTS) methods have become decisive for the discovery and development of new biocatalysts and their application in numerous fields. Sulfatases, a broad class of biocatalysts that hydrolyze sulfate esters, are involved in diverse relevant cellular functions (e.g., signaling and hormonal regulation) and are therefore gaining importance, particularly in the medical field. Additionally, various technical applications have been recently devised. One of the major challenges in the field of enzyme development is the sensitive and high-throughput detection of the actual product of the biocatalyst of interest without the need for chromophore analogues. Addressing this issue, a colorimetric assay for sulfatases was developed and validated for detecting sulfate through a two-step enzymatic cascade, with a linear detection range of 3.3 (limit of detection) up to 250 μM. The procedure is compatible with relevant compounds employed in sulfatase reactions, including cosolvents, cations, and buffers. The assay was optimized and performed as part of a 96-well screening workflow that included bacterial growth, heterologous sulfatase expression, cell lysis, sulfate ester hydrolysis, inactivation of cell lysate, and colorimetric sulfate determination. With this procedure, the activity of an aryl and an alkyl sulfatase could be confirmed and validated. Overall, this assay provides a simple and fast alternative for screening and engineering sulfatases from DNA libraries (e.g., using metagenomics) with medical or synthetic relevance.

Microbial alkyl- and aryl-sulfatases: mechanism, occurrence, screening and stereoselectivities

This review gives an overview on the occurrence of sulfatases in Prokaryota, Eukaryota and Archaea. The mechanism of enzymes acting with retention or inversion of configuration during sulfate ester hydrolysis is discussed taking two complementary examples. Methods for the discovery of novel alkyl sulfatases are described by way of sequence-based search and enzyme induction. A comprehensive list of organisms with their respective substrate scope regarding prim- and sec-alkyl sulfate esters allows to assess the capabilities and limitations of various biocatalysts employed as whole cell systems or as purified enzymes with respect to their activities and enantioselectivities. Methods for immobilization and selectivity enhancement by addition of metal ions or organic (co)solvents are summarised.

Inverting hydrolases and their use in enantioconvergent biotransformations

•

Enantioconvergent processes overcome the 50%-yield limits of kinetic resolution.

•

Inverting enzymes are key catalysts for enantioconvergent processes.

•

Enzyme engineering provided improved variants of inverting enzymes.

Owing to the more abundant occurrence of racemic compounds compared to prochiral or meso forms, most enantiomerically pure products are obtained via racemate resolution. This review summarizes (chemo)enzymatic enantioconvergent processes based on the use of hydrolytic enzymes, which are able to invert a stereocenter during catalysis that can overcome the 50%-yield limitation of kinetic resolution. Recent developments are presented in the fields of inverting or retaining sulfatases, epoxide hydrolases and dehalogenases, which allow the production of secondary alcohols or vicinal diols at a 100% theoretical yield from a racemate via enantioconvergent processes.

A stereoselective inverting sec-alkylsulfatase for the deracemization of sec-alcohols

A metallo-β-lactamase-type alkylsulfatase was found to catalyze the enantioselective hydrolysis of sec-alkylsulfates with strict inversion of configuration. This catalytic event, which does not have an analog in chemocatalysis, yields homochiral (S)-configurated alcohols and nonreacted sulfate esters. The latter could be converted into (S)-sec-alcohols as the sole product in up to >99% ee via a chemoenzymatic deracemization protocol on a preparative scale.