Identification of essential histidines in cyclodextrin glycosyltransferase isoform 1 from Paenibacillus sp. A11

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.

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

Purification and characterization of a cyclomaltodextrin glucanotransferase from Paenibacillus campinasensis strain H69-3

A cyclomaltodextrin glucanotransferase (E.C. 2.4.1.19) from a newly isolated alkalophilic and moderately thermophilic Paenibacillus campinasensis strain H69-3 was purified as a homogeneous protein from culture supernatant. Cyclomaltodextrin glucanotransferase was produced during submerged fermentation at 45 degrees C and purified by gel filtration on Sephadex G50 ion exchange using a Q-Sepharose column and ion exchange using a Mono-Q column. The molecular weight of the purified enzyme was 70 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the pI was 5.3. The optimum pH for enzyme activity was 6.5, and it was stable in the pH range 6.0-11.5. The optimum temperature was 65 degrees C at pH 6.5, and it was thermally stable up to 60 degrees C without substrate during 1 h in the presence of 10 mM CaCl(2). The enzyme activity increased in the presence of Co(2+), Ba(2+), and Mn(2+). Using maltodextrin as substrate, the K(m) and K(cat) were 1.65 mg/mL and 347.9 micromol/mg x min, respectively.

Structure-function relationship in cyclodextrin glycosyltransferase from Bacillus circulans DF 9R

Cyclodextrin glycosyltransferases (CGTases E.C.2.4.1.19) catalyze cyclomaltooligosaccharides (cyclodextrins) production, an important industrial process. We herein report structural features of Bacillus circulans DF 9R cyclodextrin glycosyltransferase including its sequence and several aspects of enzyme structure-function relationship. Protein ethoxyformylation, under our experimental conditions, indicated that only one out of the 13 enzyme histidines was modified leading to a drastic drop in cyclizing and hydrolytic activity. Besides, tryptic digestion of the (14)C ethoxyformylated protein and studies of the peptide mixture showed that histidine 233 is the most reactive histidine residue. This is the first cyclodextrin glycosyltransferase with a known primary structure and a glutamine instead of glycine residue at position 179 in the highly conserved -6 subsite, shown to be involved in substrate binding. The presence of glycine at that position was considered as a requirement for such binding following the induced-fit mechanism already proposed. Moreover, the enzyme has all the features previously described for an alpha- or alpha/beta-cyclodextrin producer.