Fusion of maltooligosaccharide-forming amylases from two origins for the improvement of maltopentaose synthesis

Improvement of combined cross-linked enzyme aggregates of cyclodextrin glucanotransferase and maltogenic amylase by functionalization of cross-linker for maltooligosaccharides synthesis

Combined cross-linked enzyme aggregates of cyclodextrin glucanotransferase (CGTase) and maltogenic amylase (Mag1) from Bacillus lehensis G1 (Combi-CLEAs-CM) were successfully developed to synthesis maltooligosaccharides (MOS). Yet, the poor cross-linking performance between chitosan (cross-linker) and enzymes resulting low activity recovery and catalytic efficiency. In this study, we proposed the functionalization of cross-linkers with the integration of computational analysis to study the influences of different functional group on cross-linkers in combi-CLEAs development. From in-silico analysis, O-carboxymethyl chitosan (OCMCS) with the highest binding affinity toward both enzymes was chosen and showed alignment with the experimental result, in which OCMCS was synthesized as cross-linker to develop improved activity recovery of Combi-CLEAs-CM-ocmcs (74 %). The thermal stability and deactivation energy (205.86 kJ/mol) of Combi-CLEAs-CM-ocmcs were found to be higher than Combi-CLEAs-CM (192.59 kJ/mol). The introduction of longer side chain of carboxymethyl group led to a more flexible structure of Combi-CLEAs-CM-ocmcs. This alteration significantly reduced the Km value of Combi-CLEAs-CM-ocmcs by about 3.64-fold and resulted in a greater Kcat/Km (3.63-fold higher) as compared to Combi-CLEAs-CM. Moreover, Combi-CLEAs-CM-ocmcs improved the reusability with retained >50 % of activity while Combi-CLEAs-CM only 36.18 % after five cycles. Finally, maximum MOS production (777.46 mg/g) was obtained by Combi-CLEAs-CM-ocmcs after optimization using response surface methodology.

Improving the Product Specificity of Maltotetraose-Forming Amylase from Pseudomonas saccharophila STB07 by Removing the Carbohydrate-Binding Module

Maltotetraose (G4) is composed of four glucose units linked by the α-1,4-glycosidic bond, which has excellent adaptability in food processing and specific physiological functions. Maltotetraose-forming amylases (MFAses) are used in the industry as a promising tool for G4 production. The MFAse from Pseudomonas saccharophila STB07 (MFA_PS), which belongs to the GH13, can preferentially hydrolyze substrates to G4. MFA_PS contains a carbohydrate-binding module (CBM). In this study, we removed the CBM to obtain the mutant MFA_PS-ΔCBM. We explored the aspects affecting the catalytic performance of enzymes through structural simulations and molecular docking. Results showed that when the CBM was removed, the thermal stability of MFA_PS was slightly reduced, and its catalytic ability for long-chain substrates, such as corn starch, was significantly reduced. However, the catalytic ability and product specificity of the substrates with shorter chain length, such as maltodextrin (DE 7-9), were improved. The G1-G7 (glucose (G1), maltose (G2), maltotriose (G3), maltotetraose (G4), maltopentaose (G5), maltohexaose (G6), and maltoheptaose (G7)) contents and G4 proportion of the mutant MFA_PS-ΔCBM reaction at 24 h were 11.1 and 11.6% higher than those of MFA_PS, respectively. The results also showed that the forces of MFA_PS on the substrate near the -4, -1, +1, and +3 subsites were critical for its product specificity.

Starch-Binding Domain Modulates the Specificity of Maltopentaose Production at Moderate Temperatures

Maltooligosaccharide-forming amylases (MFAs) hydrolyze starch into maltooligosaccharides with a defined degree of polymerization. However, the enzymatic mechanism underlying the product specificity remains partially understood. Here, we show that Saccharophagus degradans MFA (SdMFA) contains a noncatalytic starch-binding domain (SBD), which belongs to the carbohydrate-binding module family 20 and enables modulation of the product specificity. Removal of SBD from SdMFA resulted in a 3.5-fold lower production of the target maltopentaose. Conversely, appending SBD to another MFA from Bacillus megaterium improved the specificity for maltopentaose. SdMFA exhibited a higher level of exo-action and greater product specificity when reacting with amylopectin than with amylose. Our structural analysis and molecular dynamics simulation suggested that SBD could promote the recognition of nonreducing ends of substrates and delivery of the substrate chain to a groove end toward the active site in the catalytic domain. Furthermore, we demonstrate that a moderate temperature could mediate SBD to interact with the substrate with loose affinity, which facilitates the substrate to slide toward the active site. Together, our study reveals the structural and conditional bases for the specificity of MFAs, providing generalizable strategies to engineer MFAs and optimize the biosynthesis of maltooligosaccharides.