Mutations affecting the activity of the cyclodextrin glucanotransferase of Paenibacillus pabuli US132: insights into the low hydrolytic activity of cyclodextrin glucanotransferases

Highlight on mutations affecting the US132 cyclodextrin glucanotransferase binding specificity, thermal stability, and anti-staling activity

We have already reported that the triple mutant (K47E-S382P-N655S of Paenibacillus pabuli US132 cyclodextrin glucanotransferase US132 (CGTase)) altered the CGTase specificity. In the current study, the single (K47E, S382P and N655S) and double (K47E+S382P, K47E+N655S, and S382P+N655S) mutants were constructed to elucidate the synergic or antagonist substitutions effect on the enzyme behavior. For the six generated mutants, an improvement of the dextrinization/cyclization ratio from 4.4 to 6-fold was observed when compared to the wild-type enzyme. The mutations effect on enzyme specificity was not attributed to synergy modulation since the single mutant N655S had the highest ratio enhancement. Moreover, the mutant N655S revealed the highest β-cyclodextrin binding affinity with a high amount of hydrophobic bonds which might be contributed to the apparent decrease in the cyclization activity. On the other hand, mutations N655S, K47E, and (K47E-N655S) showed the same positive effect on thermal activity. The highest stability was attained at 70 °C by N655S to be 3.6-fold higher than the wild-type. The addition of N655S to wheat flour induced a decrease of dough and bread hardness and led to an increase in dough and bread cohesiveness and a rise in bread masticability values compared to the control. This mutant addition also corrected the dough elasticity decrease engendered by the wild-type CGTase indicating that N655S-CGTase could be an alternative anti-staling agent.

Molecular cloning, and optimized production and characterization of recombinant cyclodextrin glucanotransferase from Bacillus sp. T1

Cyclodextrin glucosyltransferase (CGTase) is an enzyme which degrades starch to produce cyclodextrins (CDs). In this study, the β-CGTase producing strain T1 was identified as Bacillus sp. by its morphological characteristics and 16S rDNA sequence analysis. The cgt-T1 gene was cloned and expressed in Escherichia coli. CGTase-T1 was purified by Ni-nitrilotriacetic acid agarose column and the molecular weight was determined as approximately 75 kDa using SDS-PAGE analysis. For the expression of soluble proteins, the optimal induction conditions were 10 h at 25 °C with OD₆₀₀ at 0.8. The purified CGTase-T1 exhibited maximum activity with an optimal pH and temperature of 6.0 and 65 °C. The enzyme was stable in a pH range of 7.0-10.0, retaining over 85% relative activity for 1 h. CGTase-T1 activity can be significantly enhanced by adding 1 mM Ba²⁺. Using a soluble starch substrate, the kinetic parameters were revealed with K _M and k _cat/K _M values of 2.75 mg mL^-1 and 1253.97 s^-1 mL mg^-1, respectively. Additionally, the four enzyme activities of CGTase-T1 were determined. The highest conversion rate to CDs (40.9%) was achieved from soluble starch after 8 h of enzyme reaction, where mainly β-CD was produced (79.1% of the total CDs yield), indicating that CGTase-T1 potentially has industrial application prospect.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-022-03111-8.

US132 Cyclodextrin Glucanotransferase Engineering by Random Mutagenesis for an Anti-Staling Purpose

The use of the cyclodextrin glucanotransferase (CGTase) of the US132 strain, which is an effective anti-staling agent, has been hampered by its high cyclization activity. Since that random mutagenesis using error-prone PCR is nowadays a method of choice for enzymes engineering, we have optimized this method by adjusting manganese concentration in order to obtain a high percentage of active CGTase mutants. Therefore, the amplification of the gene encoding the US132 CGTase was performed using a MnCl2 concentration ranging between 0 and 0.5 mM. The finding showed that a manganese concentration of 0.04 mM allowed for 90 % of active mutants. A simple method to rapidly screen the obtained mutants was also developed. After the examination of a small library (of less than 1000 clones), the active mutant named MJ13 was selected for a significant decrease in the cyclization activity, thereby showing a remarkable change in the enzyme specificity towards starch dextrinizing. Sequence analysis showed that MJ13 is a triple mutant with two mutations in the catalytic domain (K47E and S382P) and one substitution in the starch binding domain (N655S).

Glycosynthesis in a waterworld: new insight into the molecular basis of transglycosylation in retaining glycoside hydrolases

Carbohydrates are ubiquitous in Nature and play vital roles in many biological systems. Therefore the synthesis of carbohydrate-based compounds is of considerable interest for both research and commercial purposes. However, carbohydrates are challenging, due to the large number of sugar subunits and the multiple ways in which these can be linked together. Therefore, to tackle the challenge of glycosynthesis, chemists are increasingly turning their attention towards enzymes, which are exquisitely adapted to the intricacy of these biomolecules. In Nature, glycosidic linkages are mainly synthesized by Leloir glycosyltransferases, but can result from the action of non-Leloir transglycosylases or phosphorylases. Advantageously for chemists, non-Leloir transglycosylases are glycoside hydrolases, enzymes that are readily available and exhibit a wide range of substrate specificities. Nevertheless, non-Leloir transglycosylases are unusual glycoside hydrolases in as much that they efficiently catalyse the formation of glycosidic bonds, whereas most glycoside hydrolases favour the mechanistically related hydrolysis reaction. Unfortunately, because non-Leloir transglycosylases are almost indistinguishable from their hydrolytic counterparts, it is unclear how these enzymes overcome the ubiquity of water, thus avoiding the hydrolytic reaction. Without this knowledge, it is impossible to rationally design non-Leloir transglycosylases using the vast diversity of glycoside hydrolases as protein templates. In this critical review, a careful analysis of literature data describing non-Leloir transglycosylases and their relationship to glycoside hydrolase counterparts is used to clarify the state of the art knowledge and to establish a new rational basis for the engineering of glycoside hydrolases.