ascorbic-acid-2-o-glucoside and maltodextrin

By engineering the subsite +1 of cyclodextrin glycosyltransferase (CGTase) from Paenibacillus macerans, we improved its maltodextrin specificity for 2-O-D-glucopyranosyl-L-ascorbic acid (AA-2G) synthesis. Specifically, we conducted site-saturation mutagenesis on Leu194, Ala230, and His233 in subsite +1 separately and gained 3 mutants L194N (leucine --> asparagine), A230D (alanine --> aspartic acid), and H233E (histidine --> glutamic acid) produced higher AA-2G yield than the wild-type and the other mutant CGTases. Therefore, the 3 mutants L194N, A230D, and H233E were further used to construct the double and triple mutations. Among the 7 obtained combinational mutants, the triple mutant L194N/A230D/H233E produced the highest AA-2G titer of 1.95 g/L, which was increased by 62.5% compared with that produced by the wild-type CGTase. Then, we modeled the reaction kinetics of all the mutants and found a substrate inhibition by high titer of L-AA for the mutants. The optimal temperature, pH, and reaction time of all the mutants were also determined. The structure modeling indicated that the enhanced maltodextrin specificity may be related with the changes of hydrogen bonding interactions between the side chain of residue at the three positions (194, 230 and 233) and the substrate sugars.

Topics: Ascorbic Acid; Glucosyltransferases; Hydrogen Bonding; Kinetics; Mutagenesis, Site-Directed; Paenibacillus; Polysaccharides; Protein Engineering; Substrate Specificity; Temperature

In this work, the subsite-3 of cyclodextrin glycosyltransferase (CGTase) from Paenibacillus macerans was engineered to improve maltodextrin specificity for 2-O-d-glucopyranosyl-l-ascorbic acid (AA-2G) synthesis. Specifically, the site-saturation mutagenesis of tyrosine 89, asparagine 94, aspartic acid 196, and aspartic acid 372 in subsite-3 was separately performed, and three mutants Y89F (tyrosine→phenylalanine), N94P (asparagine→proline), and D196Y (aspartic acid→tyrosine) produced higher AA-2G titer than the wild-type and the other mutants. Previously, we found the mutant K47L (lysine→leucine) also had a higher maltodextrin specificity. Therefore, the four mutants K47L, Y89F, N94P, and D196Y were further used to construct the double, triple, and quadruple mutations. Among the 11 combinational mutants, the quadruple mutant K47L/Y89F/N94P/D196Y produced the highest AA-2G titer of 2.23g/L, which was increased by 85.8% compared to that produced by the wild-type CGTase. The reaction kinetics of all the mutants were modeled, and the pH and thermal stabilities of all the mutants were analyzed. The structure modeling indicated that the enhanced maltodextrin specificity may be related with the changes of hydrogen bonding interactions between the side chain of residue at the four positions (47, 89, 94, and 196) and the substrate sugars.

Topics: Amino Acid Substitution; Ascorbic Acid; Base Sequence; Enzyme Stability; Glucosyltransferases; Hydrogen-Ion Concentration; Kinetics; Models, Molecular; Mutagenesis, Site-Directed; Mutant Proteins; Paenibacillus; Polysaccharides; Protein Engineering; Substrate Specificity; Temperature

In this work, the site-saturation engineering of lysine 47 in cyclodextrin glycosyltransferase (CGTase) from Paenibacillus macerans was conducted to improve the specificity of CGTase towards maltodextrin, which can be used as a cheap and easily soluble glycosyl donor for the enzymatic synthesis of 2-O-D-glucopyranosyl-L-ascorbic acid (AA-2G) by CGTase. When using maltodextrin as glycosyl donor, four mutants K47F (lysine→ phenylalanine), K47L (lysine→ leucine), K47V (lysine→ valine) and K47W (lysine→ tryptophan) showed higher AA-2G yield as compared with that produced by the wild-type CGTase. The transformation conditions (temperature, pH and the mass ratio of L-ascorbic acid to maltodextrin) were optimized and the highest titer of AA-2G produced by the mutant K47L could reach 1.97 g/l, which was 64.2% higher than that (1.20 g/l) produced by the wild-type CGTase. The reaction kinetics analysis confirmed the enhanced maltodextrin specificity, and it was also found that compared with the wild-type CGTase, the four mutants had relatively lower cyclization activities and higher disproportionation activities, which was favorable for AA-2G synthesis. The mechanism responsible for the enhanced substrate specificity was further explored by structure modeling and it was indicated that the enhancement of maltodextrin specificity may be due to the short residue chain and the removal of hydrogen bonding interactions between the side chain of residue 47 and the sugar at -3 subsite. Here the obtained mutant CGTases, especially the K47L, has a great potential in the production of AA-2G with maltodextrin as a cheap and easily soluble substrate.

Topics: Amino Acid Substitution; Ascorbic Acid; Enzyme Stability; Glucosyltransferases; Hydrogen-Ion Concentration; Kinetics; Lysine; Models, Molecular; Mutagenesis, Site-Directed; Mutant Proteins; Paenibacillus; Polysaccharides; Protein Conformation; Substrate Specificity; Temperature

In this work, the site saturation mutagenesis of tyrosine 195, tyrosine 260 and glutamine 265 in the cyclodextrin glycosyltransferase (CGTase) from Paenibacillus macerans was conducted to improve the specificity of CGTase for maltodextrin, which can be used as a cheap and easily soluble glycosyl donor for the synthesis of 2-O-d-glucopyranosyl-l-ascorbic acid (AA-2G). Specifically, the site-saturation mutagenesis of three sites-tyrosine 195, tyrosine 260, and glutamine 265-was performed, and it was found that the resulting mutants (containing the mutations Y195S [tyrosine → serine], Y260R [tyrosine → arginine], and Q265K [glutamine → lysine]) produced higher AA-2G yields than the wild type and the other mutant CGTases when maltodextrin was used as the glycosyl donor. Furthermore, double and triple mutations were introduced, and four mutants (containing Y195S/Y260R, Y195S/Q265K, Y260R/Q265K, and Y260R/Q265K/Y195S) were obtained and evaluated for the capacity to produce AA-2G. The Y260R/Q265K/Y195S triple mutant produced the highest titer of AA-2G at 1.92 g/liter, which was 60% higher than that (1.20 g/liter) produced by the wild-type CGTase. The kinetics analysis of AA-2G synthesis by the mutant CGTases confirmed the enhanced maltodextrin specificity, and it was also found that compared with the wild-type CGTase, all seven mutants had lower cyclization activities and higher hydrolysis and disproportionation activities. Finally, the mechanism responsible for the enhanced substrate specificity was explored by structure modeling, which indicated that the enhancement of maltodextrin specificity may be related to the changes of hydrogen bonding interactions between the side chain of residue at the three positions (195, 260, and 265) and the substrate sugars. This work adds to our understanding of the synthesis of AA-2G and makes the Y260R/Q265K/Y195S mutant a good starting point for further development by protein engineering.

Topics: Amino Acid Substitution; Ascorbic Acid; Glucosyltransferases; Kinetics; Mutagenesis, Site-Directed; Mutant Proteins; Paenibacillus; Polysaccharides; Protein Engineering; Substrate Specificity