Substrate complexation and aggregation influence the cyclodextrin glycosyltransferase (CGTase) catalyzed synthesis of alkyl glycosides

Synthesis of novel oligomeric anionic alkyl glycosides using laccase/TEMPO oxidation and cyclodextrin glucanotransferase (CGTase)-catalyzed transglycosylation

Modification of alkyl glycosides, to alter their properties and widen the scope of potential applications, is of considerable interest. Here, we report the synthesis of new anionic alkyl glycosides with long carbohydrate chains, using two different approaches: laccase/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation of a long-carbohydrate-chain alkyl glycoside and cyclodextrin glucanotransferase (CGTase)-catalyzed elongation of anionic alkyl glycosides. The laccase/TEMPO oxidation of dodecyl β- d-maltooctaoside proceeded efficiently with the formation of aldehyde and acid products. However, depolymerization occurred to a large extent, limiting the product yield and purity. On the other hand, CGTase-catalyzed coupling/disproportionation reactions with α-cyclodextrin and dodecyl β- d-maltoside diuronic acid (DDM-2COOH) or octyl β- d-glucuronic acid (OG-COOH) as substrates gave high conversions, especially when the CGTase Toruzyme was used. It was found that pH had a strong influence on both the enzyme activity and the acceptor specificity. With non-ionic substrates (dodecyl β- d-maltoside and octyl β- d-glucoside), Toruzyme exhibited high catalytic activity at pH 5-6, but for the acidic substrates (DDM-2COOH and OG-COOH) the activity was highest at pH 4. This is most likely due to the enzyme favoring the protonated forms of DDM-2COOH and OG-COOH, which exist at lower pH (pKa about 3).

Effects of immobilization, pH and reaction time in the modulation of α-, β- or γ-cyclodextrins production by cyclodextrin glycosyltransferase: Batch and continuous process

This study reports the immobilization of a β-CGTase on glutaraldehyde pre-activated silica and its use to production of cyclodextrins in batch and continuous reactions. We were able to modulate the cyclodextrin production (α-, β- and γ-CD) by immobilization and changing the reaction conditions. In batch reactions, the immobilized enzyme reached to maximum productions of 4.9mgmL^-1 of α-CD, 3.6mgmL^-1 of β-CD and 3.5mgmL^-1 of γ-CD at different conditions of temperature, pH and reaction time. In continuous reactor, varying the residence time and pH it was possible to produce at pH 4.0 and 141min of residence time preferentially γ-CD (0.75 and 3.36mgmL^-1 of α- and γ-CD, respectively), or at pH 8.0 and 4.81min α- and β-CDs (3.44 and 3.51mgmL^-1).

Complexation of alkyl glycosides with α-cyclodextrin can have drastically different effects on their conversion by glycoside hydrolases

Substrates present in aggregated forms, such as micelles, are often poorly converted by enzymes. Alkyl glycosides constitute typical examples and the critical micelle concentration (CMC) decreases with increasing length of the alkyl group. In this study, possibilities to hydrolyse alkyl glycosides by glycoside hydrolases were explored, and α-cyclodextrin was used as an agent to form inclusion complexes with the alkyl glycosides, thereby preventing micelle formation. The cyclodextrin complexes were accepted as substrates by the enzymes to variable extent. The β-glucosidases originating from Thermotoga neapolitana (Tn Bgl3B) and from almond were not at all able to hydrolyse alkyl β-glucosides in the presence of 100mM α-cyclodextrin. However, Aspergillus niger amyloglucosidase readily accepted the complexes as substrates. In reactions involving decyl and dodecyl maltosides, the presence of 100mM α-cyclodextrin caused an increase in reaction rate in most cases, especially at high substrate concentrations. Surprisingly, the amyloglucosidase-catalyzed hydrolysis of octyl-β-maltoside to glucose and β-octylglucoside was faster in the presence of α-cyclodextrin than without, even at substrate concentrations below CMC. A possible explanation of the observed rate enhancement is that binding sites on the carbohydrate binding domain of amyloglucosidase, known to bind cyclodextrins, help to guide the alkyl glycoside-cyclodextrin complex to the active site, and thereby promote its conversion.

Enhanced production of α-cyclodextrin glycosyltransferase in Escherichia coli by systematic codon usage optimization

Enhancing the production of α-cyclodextrin glycosyltransferase (α-CGTase) is a key aim in α-CGTase industries. Here, the mature α-cgt gene from Paenibacillus macerans JFB05-01 was redesigned with systematic codon optimization to preferentially match codon frequencies of Escherichia coli without altering the amino acid sequence. Following synthesis, codon-optimized α-cgt (coα-cgt) and wild-type α-cgt (wtα-cgt) genes were cloned into pET-20b(+) and expressed in E. coli BL21(DE3). The total protein yield of the synthetic gene was greater than wtα-cgt expression (1,710 mg L−1) by 2,520 mg L−1, with the extracellular enzyme activity being improved to 55.3 U mL−1 in flask fermentation. ΔG values at -3 to +50 of the pelB site of both genes were −19.10 kcal mol−1. Functionally, coα-CGTase was equally as effective as wtα-CGTase in forming α-cyclodextrin (α-CD). These findings suggest that preferred codon usage is advantageous for translational efficiency to increase protein expression. Finally, batch fermentation was applied, and the extracellular coα-CGTase enzyme activity was 326 % that of wtα-CGTase. The results suggest that codon optimization is a reasonable strategy to improve the yield of α-CGTase for industrial application.