Discovery of a novel thermostable Zn2+ -dependent alcohol dehydrogenase from Chloroflexus aurantiacus through conserved domains mining.

AIMS: The purpose of the study was to demonstrate feasibility of the Conserved Domains Database (CDD) for identification of novel biocatalysts with desirable properties from a class of well-characterized biocatalysts. METHODS AND RESULTS: The thermostable ADH from Sulfolobus solfataricus with a broad substrate range was applied as a template for the search for novel thermostable ADHs via CDD. From the resulting hits, a putative ADH gene from the thermophilic organism Chloroflexus aurantiacus was cloned and expressed in Escherichia coli. The resulting enzyme was purified and characterized. With a temperature activity optimum of 70°C and a broad substrate spectrum especially for diketones, a versatile new biocatalyst was obtained. CONCLUSIONS: Database-based mining in CDD is a suitable approach to obtain novel biocatalysts with desirable properties. Thereby, the available diversity of similar but not equal enzymes within this class can be increased. SIGNIFICANCE AND IMPACT OF THE STUDY: For industrial applications, there is a demand for larger diversity of similar well-characterized enzymes in order to test them for a given process (biodiversity screening). For fundamental science, the comparison of enzymes with similar function but different sequence can provide insight into structure function relationships or the evolution of enzymes. This study gives a good example on how this demand can be efficiently met.

Biocatalytically active silCoat-composites entrapping viable Escherichia coli.

Application of whole cells in industrial processes requires high catalytic activity, manageability, and viability under technical conditions, which can in principle be accomplished by appropriate immobilization. Here, we report the identification of carrier material allowing exceptionally efficient adsorptive binding of Escherichia coli whole cells hosting catalytically active carbonyl reductase from Candida parapsilosis (CPCR2). With the immobilizates, composite formation with both hydrophobic and hydrophilized silicone was achieved, yielding advanced silCoat-material and HYsilCoat-material, respectively. HYsilCoat-whole cells were viable preparations with a cell loading up to 400 mg(E. coli) · g(-1)(carrier) and considerably lower leaching than native immobilizates. SilCoat-whole cells performed particularly well in neat substrate exhibiting distinctly increased catalytic activity.

Mechanistic model for prediction of formate dehydrogenase kinetics under industrially relevant conditions.

Formate dehydrogenase (FDH) from Candida boidinii is an important biocatalyst for the regeneration of the cofactor NADH in industrial enzyme-catalyzed reductions. The mathematical model that is currently applied to predict progress curves during (semi-)batch reactions has been derived from initial rate studies. Here, it is demonstrated that such extrapolation from initial reaction rates to performance during a complete batch leads to considerable prediction errors. This observation can be attributed to an invalid simplification during the development of the literature model. A novel mechanistic model that describes the course and performance of FDH-catalyzed NADH regeneration under industrially relevant process conditions is introduced and evaluated. Based on progress curve instead of initial reaction rate measurements, it was discriminated from a comprehensive set of mechanistic model candidates. For the prediction of reaction courses on long time horizons (>1 h), decomposition of NADH has to be considered. The model accurately describes the regeneration reaction under all conditions, even at high concentrations of the substrate formate and thus is clearly superior to the existing model. As a result, for the first time, course and performance of NADH regeneration in industrial enzyme-catalyzed reductions can be accurately predicted and used to optimize the cost efficiency of the respective processes.

Biochemical peculiarities of benzaldehyde lyase from Pseudomonas fluorescens Biovar I in the dependency on pH and cosolvent concentration.

Benzaldehyde lyase from Pseudomonas fluorescens (BAL, EC 4.1.2.38) is a versatile catalyst for stereoselective carboligations. Nevertheless, rather inconsistent data about its biochemical properties are reported in literature. In this study, the dependency of BAL activity on ionic strength, pH, and concentration of DMSO was for the first time systematically investigated and interpreted. It was found that the activity of BAL strongly depends on all three parameters, and a correlation exists between the dependency on pH and DMSO concentration. This correlation could be explained by an interaction of DMSO with an ionic amino acid in the catalytic site. A model-based analysis indicated that the pK(a) of this residue shifts to the alkaline milieu upon addition of DMSO. Consequently, the optimum pH also shifts to alkaline values when DMSO is present. Potentiometric experiments confirmed that the pK(a) can most probably be attributed to Glu50 which governs the activity increase of BAL on the acidic limb of its pH-activity profile. With these findings, the apparently contradicting data from literature become comprehensible and optimal reaction conditions for synthesis can easily be deduced.

New approaches to the visualization, quantification and explanation of acid-induced water loss from Ca-alginate hydrogel beads.

The water loss of Ca-alginate hydrogels at pHs below 4.0 was visualized with 1HNMR-imaging by covering a single alginate bead with cyclohexane-d12 in a specially equipped NMR-tube and adding propionic acid at defined concentrations. The exact amount of water expelled from the beads was calculated from their weight loss and correlated with the acid concentrations and pHs within the hydrogel matrix. The maximum water loss of 52% (w/w) occurred at pH 1.0, while only 5% (w/w) of the initial water content were lost at pH 3.6. The analysis of the water collected from several alginate beads for Ca2+ -ions and free polysaccharides led to the assumption that, due to the acid-induced protonation of the carboxyl functions, the ionotropic network is gradually converted to an alginic acid gel structured by H-bonds. This contradicts existing theories explaining the pH-induced water loss by a lower solubility of the alginate chains and decreased repulsion between protonated carboxyl functions, but explains previously reported pH-dependent alterations of mass transport and drug retention of Ca-alginate gels. Thus, the presented experiments enable a more precise and complete view of the acid-induced process within Ca-alginate hydrogels. The transfer to the characterization of other hydrogels is possible and should be advantageous, especially if a calibration of the NMR-measurement could be achieved.

Novel solvent-based method for preparation of alginate beads with improved roundness and predictable size.

Attempts to determine conditions or processes within alginate gel beads often suffer from inaccuracies due to an improper roundness of the analysed beads. Therefore, a novel solvent-based method for the preparation of alginate beads with improved shape was developed: An aqueous solution of 2% (w/v) alginate in water was injected into a solvent layering consisting of hexane, n-butanol, n-butanol with 1% (w/v) CaCl2 and finally 2% (w/v) CaCl2 in water. Beads of up to 3.5 mm in diameter obtained with this method had a roundness which was approximately 5% better than comparable beads prepared by dropping an alginate solution into a CaCl2-hardening bath. This was determined by a software supported quantitative analysis of bead size and shape. Additionally, the novel solvent-based method allows for highly reproducible preparation of alginate beads with exactly predictable sizes. The biggest beads obtained with this method were 9 mm in diameter. Thus, with the solvent-based preparation of alginate beads it is now possible to easily obtain beads of exactly the type needed for a specific analytical purpose.