Selectivity-enhancement in enantioselective hydrolysis of sec-alkyl sulfates by an alkylsulfatase from Rhodococcus ruber DSM 44541

A review on Arthrobacter sp. lipase: A versatile biocatalyst for the kinetic resolution to access enantiomerically pure/enriched compounds

Over the last few years, there has been a dramatic increase in the number of reports related to Arthrobacter sp. lipase (ABL:MTCC No. 5125) catalyzed kinetic resolution performed in biphasic media. A strain displaying esterase/lipase activity and designated as ABL was isolated, during the course of a screening program at Indian Institute of Integrative Medicine, Jammu. Considerable research has shown that reactions catalyzed by ABL are more selective than many commercial lipases. Since new applications of this lipase are emerging, there is a great need to provide all the relevant information exclusively. This review article is an attempt to cover all the relevant reports based on isolation, purification, immobilization, and application of ABL in the biopharmaceutical sector.

Rhodococcus as A Versatile Biocatalyst in Organic Synthesis

The application of purified enzymes as well as whole-cell biocatalysts in synthetic organic chemistry is becoming more and more popular, and both academia and industry are keen on finding and developing novel enzymes capable of performing otherwise impossible or challenging reactions. The diverse genus Rhodococcus offers a multitude of promising enzymes, which therefore makes it one of the key bacterial hosts in many areas of research. This review focused on the broad utilization potential of the genus Rhodococcus in organic chemistry, thereby particularly highlighting the specific enzyme classes exploited and the reactions they catalyze. Additionally, close attention was paid to the substrate scope that each enzyme class covers. Overall, a comprehensive overview of the applicability of the genus Rhodococcus is provided, which puts this versatile microorganism in the spotlight of further research.

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.

New enzymes for biotransformations: microbial alkyl sulfatases displaying stereo- and enantioselectivity

The majority of hydrolytic enzymes used in white biotechnology for the production of non-natural compounds--such as carboxyl ester hydrolases, lipases and proteases--show a certain preference for a given enantiomer. However, they are unable to alter the stereochemistry of the substrate during catalysis with respect to inversion or retention of configuration. The latter can be achieved by (alkyl) sulfatases, which can be employed for the enantio-convergent transformation of racemic sulfate esters into a single stereoisomeric secondary alcohol, with a theoretical yield of 100%. This is a major improvement over traditional kinetic resolution processes, which yield both enantiomers, each at 50%.

Biocatalytic approaches for the quantitative production of single stereoisomers from racemates

Strategies for the chemoenzymatic transformation of a racemate into a single stereoisomeric product in quantitative yield have been developed. A range of industrially relevant α-hydroxycarboxylic acids was deracemized in a stepwise fashion via lipase-catalysed enantioselective O-acylation, followed by mandelate racemase-catalysed racemization of the remaining non-reacted substrate enantiomer. Alternatively, aliphatic α-hydroxycarboxylic acids were enzymatically isomerized using whole resting cells of Lactobacillus spp. Enantioselective hydrolysis of rac-sec-alkyl sulphate esters was accomplished using novel alkyl sulphatases of microbial origin. The stereochemical path of catalysis could be controlled by choice of the biocatalyst. Whereas Rhodococcus ruber DSM 44541 and Sulfolobus acidocaldarius DSM 639 act through inversion of configuration, stereo-complementary retaining sulphatase activity was detected in the marine planctomycete Rhodopirellula baltica DSM 10527.

Trends and challenges in enzyme technology

Several major developments took place in the field of biocatalysis over the past few years. These include the invention of directed evolution as an extremely useful method for biocatalyst improvement on the molecular level in combination with high-throughput screening systems, methods for accessing "nonculturable" biodiversity using metagenome approaches and progress in sequence-based biocatalyst discovery. In addition, new carriers and tools for immobilization of enzymes have been developed. For the synthesis of optically active compounds impressive examples using new enzymes and major progress in dynamic kinetic resolutions of racemates took place. These achievements are summarized in this review.

New enzymes for biotransformations

Several novel bioprocesses that have little or no counterpart in traditional methodology have recently been reported. The stereoselective and enantioselective hydrolysis of sec-alkyl sulfate esters by alkyl sulfatases proceeds with inversion of configuration and furnishes a homochiral product mixture. Haloalcohol dehalogenases were shown to accept various non-natural nucleophiles, such as azide, cyanide and nitrite for the asymmetric opening of epoxides giving rise to the corresponding azido-, cyano-, and nitro-alcohols as non-natural products. Asymmetric carbon-carbon bond formation via the acyloin- and benzoin-reaction was successfully catalyzed in water by novel lyases, such as benzoylformate decarboxylase and benzaldehyde lyase. New methods for the production of chiral nonracemic alpha-L-amino acids and amines were recently reported. Enantioselective stereoinversion of racemic alpha-aryl- and alpha-aryloxycarboxylic acids via epimerase-catalyzed inversion led to a single stereoisomeric product from the racemate.

Immobilised enzymes: science or art?

Enzyme immobilisation is experiencing an important transition. Combinatorial approaches are increasingly applied in the design of robust immobilised enzymes by rational combination of fundamental immobilisation techniques (i.e. non-covalent adsorption, covalent binding, entrapment and encapsulation) or with other relevant technologies. The objective is to solve specific problems that cannot be solved by one of these basic immobilisation techniques.

Highly enantioselective stereo-inverting sec-alkylsulfatase activity of hyperthermophilic Archaea

rac-sec-Alkyl sulfate esters 1a-8a were resolved in low to excellent enantioselectivities with E-values up to >200 using whole cells of aerobically-grown hyperthermophilic sulfur-metabolizers, such as Sulfolobus solfataricus DSM 1617, Sulfolobus shibatae DSM 5389 and, most notably, Sulfolobus acidocaldarius DSM 639. Significantly enhanced selectivities were obtained using cells grown on sucrose-enriched Brock-medium. The stereochemical course of this biohydrolysis was shown to proceed with strict inversion of configuration, thus the preferred (R)-enantiomers were converted into the corresponding (S)-sec-alcohols to furnish a homochiral product mixture.

Highly Enantioselective sec-Alkyl Sulfatase Activity of Sulfolobus acidocaldarius DSM 639

[reaction: see text] rac-sec-Alkyl sulfate esters 1a-4a were resolved in high enantioselectivities with E-values up to >200 using whole cells of aerobically grown Sulfolobus acidocaldarius DSM 639. The stereochemical course of this biohydrolysis was shown to proceed with strict inversion of configuration; thus, the preferred (R)-enantiomers were converted into the corresponding (S)-sec-alcohols to furnish a homochiral product mixture.

Sulfatases: Structure, Mechanism, Biological Activity, Inhibition, and Synthetic Utility

Sulfatases, which cleave sulfate esters in biological systems, play a key role in regulating the sulfation states that determine the function of many physiological molecules. Sulfatase substrates range from small cytosolic steroids, such as estrogen sulfate, to complex cell-surface carbohydrates, such as the glycosaminoglycans. The transformation of these molecules has been linked with important cellular functions, including hormone regulation, cellular degradation, and modulation of signaling pathways. Sulfatases have also been implicated in the onset of various pathophysiological conditions, including hormone-dependent cancers, lysosomal storage disorders, developmental abnormalities, and bacterial pathogenesis. These findings have increased interest in sulfatases and in targeting them for therapeutic endeavors. Although numerous sulfatases have been identified, the wide scope of their biological activity is only beginning to emerge. Herein, accounts of the diversity and growing biological relevance of sulfatases are provided along with an overview of the current understanding of sulfatase structure, mechanism, and inhibition.

Use of borate to control the 5'-position-selective microbial glucosylation of pyridoxine

Nearly 100% 5'-position selectivity of transglucosylation from maltodextrin to pyridoxine (PN) by cells of Verticillium dahliae TPU 4900 was observed when the reaction was carried out with borate. The same effect of borate was observed not only during synthesis of pyridoxine 5'-alpha-D-glucoside by partially purified enzyme of this strain but also during synthesis of this compound by other microorganisms and with other enzymes (alpha-glucosidase and cyclomaltodextrin glucanotransferase). The effect was thought to be caused by the formation of a borate complex with 3- and 4'-position hydroxyl groups of PN. A decrease in the formation of pyridoxine 5'-alpha-D-glucoside was observed in the reaction with borate, but this decrease was overcome by optimizing the pH and increasing the amount of cells in the reaction mixture.

Purification and characterization of an inverting stereo- and enantioselective sec-alkylsulfatase from the gram-positive bacterium Rhodococcus ruber DSM 44541

Whole cells of Rhodococcus ruber DSM 44541 were found to hydrolyze (+/-)-2-octyl sulfate in a stereo- and enantiospecific fashion. When growing on a complex medium, the cells produced two sec-alkylsulfatases and (at least) one prim-alkylsulfatase in the absence of an inducer, such as a sec-alkyl sulfate or a sec-alcohol. From the crude cell-free lysate, two proteins responsible for sulfate ester hydrolysis (designated RS1 and RS2) were separated from each other based on their different hydrophobicities and were subjected to further chromatographic purification. In contrast to sulfatase RS1, enzyme RS2 proved to be reasonably stable and thus could be purified to homogeneity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single band at a molecular mass of 43 kDa. Maximal enzyme activity was observed at 30 degrees C and at pH 7.5. Sulfatase RS2 showed a clear preference for the hydrolysis of linear secondary alkyl sulfates, such as 2-, 3-, or 4-octyl sulfate, with remarkable enantioselectivity (an enantiomeric ratio of up to 21 [23]). Enzymatic hydrolysis of (R)-2-octyl sulfate furnished (S)-2-octanol without racemization, which revealed that the enzymatic hydrolysis proceeded through inversion of the configuration at the stereogenic carbon atom. Screening of a broad palette of potential substrates showed that the enzyme exhibited limited substrate tolerance; while simple linear sec-alkyl sulfates (C(7) to C(10)) were freely accepted, no activity was found with branched and mixed aryl-alkyl sec-sulfates. Due to the fact that prim-sulfates were not accepted, the enzyme was classified as sec-alkylsulfatase (EC 3.1.6.X).