Urea treated subtilisin as a biocatalyst for transformations in organic solvents

Improved Enantioselectivity of Subtilisin Carlsberg towards Secondary Alcohols by Protein Engineering

Generally, the catalytic activity of subtilisin Carlsberg (SC) for transacylation reactions with secondary alcohols in organic solvent is low. Enzyme immobilization and protein engineering was performed to improve the enantioselectivity of SC towards secondary alcohols. Possible amino-acid residues for mutagenesis were found by combining available literature data with molecular modeling. SC variants were created by site-directed mutagenesis and were evaluated for a model transacylation reaction containing 1-phenylethanol in THF. Variants showing high E values (>100) were found. However, the conversions were still low. A second mutation was made, and both the E values and conversions were increased. Relative to that shown by the wild type, the most successful variant, G165L/M221F, showed increased conversion (up to 36 %), enantioselectivity (E values up to 400), substrate scope, and stability in THF.

Protein-Coated Microcrystals, Combi-Protein-Coated Microcrystals, and Cross-Linked Protein-Coated Microcrystals of Enzymes for Use in Low-Water Media

Protein-coated microcrystals (PCMC) are a high-activity preparation of enzymes for use in low-water media. The protocols for the preparation of PCMCs of Subtilisin Carlsberg and Candida antarctica lipase B (CAL B) are described. The combi-PCMC concept is useful both for cascade and non-cascade reactions. It can also be beneficial to combine two different specificities of a lipase when the substrate requires it. Combi-PCMC of CALB and Palatase used for the conversion of coffee oil present in spent coffee grounds to biodiesel is described. Cross-linked protein-coated microcrystals (CL-PCMC) in some cases can give better results than PCMC. Protocols for the CLPCMC of Subtilisin Carlsberg and Candida antarctica lipase B (CAL B) are described. A discussion of their applications is also provided.

Lipase coated clusters of iron oxide nanoparticles for biodiesel synthesis in a solvent free medium

Methyl or ethyl esters of long chain fatty acids are called biodiesel. Biodiesel is synthesized by the alcoholysis of oils/fats. In this work, lipase from Thermomyces lanuginosus was precipitated over the clusters of Fe3O4 nanoparticles. This biocatalyst preparation was used for obtaining biodiesel from soybean oil. After optimization of both immobilization conditions and process parameters, complete conversion to biodiesel was obtained in 3h and on lowering the enzyme amount, as little as 1.7U of lipase gave 96% conversion in 7h. The solvent free media with oil:ethanol (w/w) of 1:4 and 40°C with 2% (w/w) water along with 20% (w/w) silica (for facilitating acyl migration) were employed for reaching this high % of conversion. The biocatalyst design enables one to use a rather small amount of lipase. This should help in switching over to a biobased production of biodiesel.

Dual bioimprinting of Thermomyces lanuginosus lipase for synthesis of biodiesel

•

High activity TLL is made by dually bioimprinting with substrate alcohol and a surfactant.

•

TLL (28 U/g of oil) bioimprinted with only the surfactants could yield 99% biodiesel from soybean oil in about 4 h.

•

Dually bioimprinted TLL (only 1.4 U/g of oil) was able to yield 99% biodiesel within 48 h

Use of biodiesel as an alternative to non-renewable sources of energy has become an attractive option in recent years. The enzymatic synthesis of biodiesel by transesterification of fats/oils with an alcohol is a much more sustainable route than the chemical method. However, cost effectiveness of the enzymatic route is a major barrier in its commercialization. In this work, a high activity biocatalyst design of Thermomyces lanuginosus lipase is made by dually bioimprinting it with substrate and a surfactant (which is believed to open up the lid covering the active site of the lipase) during precipitation of the lipase in organic solvent. When the lipase was bioimprinted with only the surfactants, 28 U of the enzyme/g of oil could yield 99% biodiesel from soybean oil in about 4 h. However, when dually bioimprinted even very low enzyme load 1.4 U/g of oil, yielded 99% biodiesel within 48 h.

Increasing importance of protein flexibility in designing biocatalytic processes

Enzymes require some flexibility for catalysis. Biotechnologists prefer stable enzymes but often this stabilization comes at the cost of reduced efficiency. Enzymes from thermophiles have low flexibility but poor catalytic rates. Enzymes from psychrophiles are less stable but show good catalytic rates at low temperature. In organic solvents enzymes perform poorly as the prior drying makes the enzyme molecules very rigid. Adding water or increasing reaction temperature improves flexibility and catalytic rates. In case of hydrolases, flexibility and enantioselectivity have interdependence. Understanding the complex role of protein flexibility in biocatalysis can help in designing biotechnological processes.