Purification and characterization of a lactonase from Erwinia cypripedii 314B that hydrolyzes ( S )-5-oxo-2-tetrahydrofurancarboxylic acid

Characterization of a phosphotriesterase-like lactonase from the hyperthermoacidophilic crenarchaeon Vulcanisaeta moutnovskia

The phosphotriesterase-like lactonase (PLL) encoded by Vmut_2255 in the hyperthermoacidophilic crenarchaeon Vulcanisaeta moutnovskia (VmutPLL), represents the only hyperthermophilic PLL homologue identified so far in addition to the previously characterized thermophilic PLLs from Sulfolobus spp. The Vmut_2255 gene was cloned, heterologously expressed in Escherichia coli; the resultant protein purified and characterized as a 82kDa homodimer (36kDa subunits). The VmutPLL converted lactones and acyl-homoserine lactones (AHLs) with comparable activities. Towards organophosphates (OP) VmutPLL showed a promiscuous but significantly lower activity and only minor activity was observed with carboxylesters. The catalytic activity strictly depended on bivalent cations (Cd(2+)>Ni(2+)>Co(2+)>Mn(2+)>Zn(2+)). Furthermore, VmutPLL showed a pH optimum around 8.0, a temperature optimum of 80°C, and thermostability with a half-life of 26min at 90°C. In this work, the stereoselectivity of a PLL enzyme was investigated for the first time using enantiopure lactones. The VmutPLL showed a slight preference but not an exclusive specificity for the (R)-enantiomers of capro- and valerolactone. The high thermal stability as well as the broad substrate spectrum towards lactones, AHLs and OPs underlines the high biotechnological potential of VmutPLL.

The PA4204 gene encodes a periplasmic gluconolactonase (PpgL) which is important for fitness of Pseudomonas aeruginosa

In Pseudomonas aeruginosa, the PA4204 gene encodes a protein with a signal peptide and a COG2706 domain of the type present in 3-carboxy-cis,cis-muconate lactonizing enzymes. A molecular model based on the structure of the Escherichia coli YbhE phosphogluconate lactonizing enzyme shows that the enzyme has a beta-propeller ('doughnut') structure and a central active site comprising one histidine, one glutamic acid and two arginines. Inactivation of the P. aeruginosa PA4204 gene had profound phenotypic effects, resulting in slowly growing small colonies which frequently gave rise to larger colonies. The small colonies did not produce pyocyanin, produced reduced amounts of N-acylhomoserine lactones, and had extremely low levels of 2-alkyl-4-quinolones (AQs), while the larger colonies produced pyocyanin and higher amounts of AQs, including the pseudomonas quinolone signal (PQS), compared with the wild-type strain. Mutagenesis of His 182 in PA4204 resulted in the inability of this protein to restore pyocyanin production in the PA4204 isogenic mutant, suggesting that this enzyme may share an active site with other lactonizing enzymes. The protein with signal peptide was expressed as a His fusion in E. coli and purified. Two forms were observed, suggesting that the protein is translocated. The purified enzyme cleaved (S)-5-oxo-2-tetrahydrofurancarboxylic acid and d-glucono-delta-lactone, demonstrating lactonase activity. Decreased expression of the cytoplasmic phosphogluconolactonase gene (pgl) was observed in the small-colony mutant, and the mutant could not grow in the presence of mannitol or gluconate, suggesting functions in the detoxification of a gluconolactone and in sugar metabolism.

Isolation and properties of a levo-lactonase from Fusarium proliferatum ECU2002: a robust biocatalyst for production of chiral lactones

A fungus strain ECU2002, capable of enantioselectively hydrolyzing chiral lactones to optically pure hydroxy acids, was newly isolated from soil samples through two steps of screening and identified as Fusarium proliferatum (Matsushima) Nirenberg. From the crude extract of F. proliferatum ECU2002, a novel levo-lactonase was purified to homogeneity, with a purification factor of 460-folds and an overall yield of 9.7%, by ultrafiltration, acetone precipitation, and chromatographic separation through DEAE-Toyopearl, Butyl-Toyopearl, Hydroxyapatite, Toyoscreen-Super Q, and TSK-gel columns. The purified enzyme is a monomer; with a molecular mass of ca 68 kDa and a pI of 5.7 as determined by two-dimensional electrophoresis. The catalytic performance of the partially purified levo-lactonase was investigated, giving temperature and pH optima at 50 degrees C and 7.5, respectively, for gamma-butyrolactone hydrolysis. The substrate specificity of the partially purified lactonase was also examined using several useful lactones, among which alpha-hydroxy-gamma-butyrolactone was the best substrate, with 448-fold higher lactonase activity as compared to gamma-butyrolactone. The F. proliferatum lactonase preferentially hydrolyzed the levo enantiomer of butyrolactones, including beta-butyrolactone, alpha-hydroxy-gamma-butyrolactone, alpha-hydroxy-beta,beta-dimethyl-gamma-butyrolactone (pantolactone), and beta-hydroxy-gamma-butyrolactone, affording (+)-hydroxy acids in high (94.8 approximately 98.2%) enantiomeric excesses (ee) and good conversions (38.2 approximately 44.2%). A simple immobilization of the crude lactonase with glutaraldehyde cross-linking led to a stable and easy-to-handle biocatalyst for catalytic resolution of chiral lactones. The immobilized lactonase also performed quite well in repeated batch resolution of dl-pantolactone at a concentration of 35% (w/v), retaining 67% of initial activity after ten cycles of reaction (corresponding to a half life of 20 cycles) and affording the product in 94 approximately 97% ee, which can be easily enhanced to >99% ee after the d-hydroxy acid was chemically converted into l-lactone and crystallized.

Cloning, sequencing, and heterologous expression of an Erwinia cypripedii 314B lactonase specific for L-alpha-hydroxyglutaric acid gamma-lactone

The gene for a lactonase that stereospecifically hydrolyzes (S)-5-oxo-2-tetrahydrofurancarboxylic acid to L-alpha-hydroxyglutaric acid was isolated from Erwinia cypripedii 314B. Determination of the nucleotide sequence showed that the gene consists of a single open reading frame of 1,152 bp that encodes a 383-amino-acid protein. Comparison of the sequence of the predicted protein to that of the enzyme purified from E. cypripedii 314B revealed an N-terminal signal sequence of 19 amino acids. The gene for the mature enzyme was inserted into a pET vector and overexpressed in Escherichia coli. Active recombinant enzyme accumulated in the cells to approximately 30% of the total protein, and the enzyme was purified to homogeneity. The physical and catalytic properties of the recombinant enzyme were indistinguishable from those of the protein purified from E. cypripedii 314B. The deduced amino acid sequence displayed approximately 35% similarity with a putative 3-carboxymuconate cyclase, but exhibited no such activity. The enzyme also showed approximately 35% similarity with 6-phosphogluconolactonase. However, the activity of the enzyme toward 6-phosphogluconolactone was less than 2% of that toward (S)-5-oxo-2-tetrahydrofurancarboxylic acid, demonstrating a novel specificity for this lactonase.