Enantioselective stereoinversion of sec-alkyl sulfates by an alkylsulfatase from Rhodococcus ruber DSM 44541

Lysophosphatidic acid signaling via LPA6 : A negative modulator of developmental oligodendrocyte maturation

The developmental process of central nervous system (CNS) myelin sheath formation is characterized by well-coordinated cellular activities ultimately ensuring rapid and synchronized neural communication. During this process, myelinating CNS cells, namely oligodendrocytes (OLGs), undergo distinct steps of differentiation, whereby the progression of earlier maturation stages of OLGs represents a critical step toward the timely establishment of myelinated axonal circuits. Given the complexity of functional integration, it is not surprising that OLG maturation is controlled by a yet fully to be defined set of both negative and positive modulators. In this context, we provide here first evidence for a role of lysophosphatidic acid (LPA) signaling via the G protein-coupled receptor LPA6 as a negative modulatory regulator of myelination-associated gene expression in OLGs. More specifically, the cell surface accessibility of LPA6 was found to be restricted to the earlier maturation stages of differentiating OLGs, and OLG maturation was found to occur precociously in Lpar6 knockout mice. To further substantiate these findings, a novel small molecule ligand with selectivity for preferentially LPA6 and LPA6 agonist characteristics was functionally characterized in vitro in primary cultures of rat OLGs and in vivo in the developing zebrafish. Utilizing this approach, a negative modulatory role of LPA6 signaling in OLG maturation could be corroborated. During development, such a functional role of LPA6 signaling likely serves to ensure timely coordination of circuit formation and myelination. Under pathological conditions as seen in the major human demyelinating disease multiple sclerosis (MS), however, persistent LPA6 expression and signaling in OLGs can be seen as an inhibitor of myelin repair. Thus, it is of interest that LPA6 protein levels appear elevated in MS brain samples, thereby suggesting that LPA6 signaling may represent a potential new druggable pathway suitable to promote myelin repair in MS.

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.

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.

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.

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).