Protein engineering of Sulfolobus solfataricus maltooligosyltrehalose synthase to alter its selectivity

Trehalose Production Using Three Extracellular Enzymes Produced via One-Step Fermentation of an Engineered Bacillus subtilis Strain

At present, the double-enzyme catalyzed method using maltooligosyltrehalose synthase (MTSase) and maltooligosyltrehalose trehalohydrolase (MTHase) is the mainstream technology for industrial trehalose production. However, MTSase and MTHase are prepared mainly using the heterologous expression in the engineered Escherichia coli strains so far. In this study, we first proved that the addition of 3 U/g neutral pullulanase PulA could enhance the trehalose conversion rate by 2.46 times in the double-enzyme catalyzed system. Then, a CBM68 domain was used to successfully assist the secretory expression of MTSase and MTHase from Arthrobacter ramosus S34 in Bacillus subtilis SCK6. At the basis, an engineered strain B. subtilis PSH02 (amyE::pulA/pHT43-C68-ARS/pMC68-ARH), which co-expressed MTSase, MTHase, and PulA, was constructed. After the 24 h fermentation of B. subtilis PSH02, the optimum ratio of the extracellular multi-enzymes was obtained to make the highest trehalose conversion rate of 80% from 100 g/L maltodextrin. The high passage stability and multi-enzyme preservation stability made B. subtilis PSH02 an excellent industrial production strain. Moreover, trehalose production using these extracellular enzymes produced via the one-step fermentation of B. subtilis PSH02 would greatly simplify the procedure for multi-enzyme preparation and be expected to reduce production costs.

Altering the substrate specificity of recombinant l-rhamnose isomerase from Thermoanaerobacterium saccharolyticum NTOU1 to favor d-allose production

l-Rhamnose isomerase (l-RhI) catalyzes rare sugar isomerization between aldoses and ketoses. In an attempt to alter the substrate specificity of Thermoanaerobacterium saccharolyticus NTOU1 l-RhI (TsRhI), residue Ile102 was changed to other polar or charged amino acid residues by site-directed mutagenesis. The results of activity-screening using different substrates indicate that I102N, I102Q, and I102R TsRhIs can increase the preference against d-allose in comparison with the wild-type enzyme. The catalytic efficiencies of the purified I102N, I102Q, and I102R TsRhIs against d-allose are 148 %, 277 %, and 191 %, respectively, of that of wild-type enzyme, while those against l-rhamnose are 100 %, 167 % and 87 %, respectively. Mutant I102N, I102Q, and I102R TsRhIs were noted to have the altered substrate specificity, and I102Q TsRhI has the highest catalytic efficiency against d-allose presumably through the formation of an additional hydrogen bond with d-allose. The purified wild-type and mutant TsRhIs were further used to produce d-allose from 100 g/L d-fructose in the presence of d-allulose 3-epimerase, and the yields can reach as high as 22 % d-allulose and 12 % d-allose upon equilibrium. I102Q TsRhI takes only around half of the time to reach the same 12 % d-allose yield, suggesting that this mutant enzyme has a potential to be applied in d-allose production.

Improved Thermostability of Maltooligosyltrehalose Synthase from Arthrobacter ramosus by Directed Evolution and Site-Directed Mutagenesis

Maltooligosyltrehalose synthase (MTSase) is a key enzyme in trehalose production. MTSase from Arthrobacter ramosus has poor thermostability, limiting its industrial use. In this study, mutant G415P was obtained by directed evolution and S361R/S444E was subsequently generated based on a structure analysis of the region around G415. The t_1/2 of G415P and S361R/S444E at 60 °C increased by 3.0- and 3.2-fold, respectively, compared with the wild-type enzyme. A triple mutant (G415P/S361R/S444E) was obtained through a combination of the above mutants, and its t_1/2 significantly increased by 19.7-fold. Kinetic and thermodynamic stability results showed that the T₅₀ and T_m values of the triple mutant increased by 7.1 and 7.3 °C, respectively, compared with those of the wild-type enzyme. When the triple mutant was used in trehalose production, the yield reached 71.6%, higher than the 70.3% achieved with the wild-type. Thus, the mutant has a potential application for industrial trehalose production.

Integrated Approach To Producing High-Purity Trehalose from Maltose by the Yeast Yarrowia lipolytica Displaying Trehalose Synthase (TreS) on the Cell Surface

An alternative strategy that integrated enzyme production, trehalose biotransformation, and bioremoval in one bioreactor was developed in this study, thus simplifying the traditional procedures used for trehalose production. The trehalose synthase gene from a thermophilic archaea, Picrophilus torridus, was first fused to the YlPir1 anchor gene and then inserted into the genome of Yarrowia lipolytica, thus yielding an engineered yeast strain. The trehalose yield reached 73% under optimal conditions. The thermal and pH stabilities of the displayed enzyme were improved compared to those of its free form purified from recombinant Escherichia coli. After biotransformation, the glucose byproduct and residual maltose were directly fermented to ethanol by a Saccharomyces cerevisiae strain. Ethanol can be separated by distillation, and high-purity trehalose can easily be obtained from the fermentation broth. The results show that this one-pot procedure is an efficient approach to the economical production of trehalose from maltose.

Identification of substrate-binding and selectivity-related residues of maltooligosyltrehalose synthase from the thermophilic archaeon Sulfolobus solfataricus ATCC 35092

Maltooligosyltrehalose synthase (MTSase) is a key enzyme in the synthesis of trehalose. Computer simulations using AutoDock and NAMD were employed to assess the substrate-binding and selectivity-related residues of MTSase. We introduced mutations at residues D411, D610, and R614 to determine the substrate-binding residues of Sulfolobus solfataricus ATCC 35092 MTSase, and introduced mutations at residues P402, A406, and V426 to investigate the enzyme's selectivity-related residues. Kinetic studies of D411A, D610A, and R614A MTSases reveal significant reductions in catalytic efficiency and cause increase in the transition-state energy of mutant MTSases, indicating that residues D411, D610, and R614 form hydrogen bonds to the substrate. Compared with wild-type MTSase, the hydrolysis: transglycosylation selectivity ratio was significantly decreased for P402Q and significantly increased for A406S MTSases, while the ratio for V426T MTSase showed little change. The results suggest that P402 and A406 residues are selectivity-related.

Interaction between trehalose and MTHase from Sulfolobus solfataricus studied by theoretical computation and site-directed mutagenesis

Maltooligosyltrehalose trehalohydrolase (MTHase) catalyzes the release of trehalose by cleaving the α-1,4-glucosidic linkage next to the α-1,1-linked terminal disaccharide of maltooligosyltrehalose. Computer simulation using the hydrogen bond analysis, free energy decomposition, and computational alanine scanning were employed to investigate the interaction between maltooligosyltrehalose and the enzyme. The same residues that were chosen for theoretical investigation were also studied by site-directed mutagenesis and enzyme kinetic analysis. The importance of residues determined either experimentally or computed theoretically were in good accord with each other. It was found that residues Y155, D156, and W218 of subsites -2 and -3 of the enzyme might play an important role in interacting with the ligand. The theoretically constructed structure of the enzyme-ligand complex was further validated through an ab initio quantum chemical calculation using the Gaussian09 package. The activation energy computed from this latter study was very similar to those reported in literatures for the same type of hydrolysis reactions.

Structure of ST0929, a putative glycosyl transferase from Sulfolobus tokodaii

The Sulfolobus tokodaii protein ST0929 shares close structural homology with S. acidocaldarius maltooligosyl trehalose synthase (SaMTSase), suggesting that the two enzymes share a common enzymatic mechanism. MTSase is one of a pair of enzymes that catalyze trehalose biosynthesis. The relative geometries of the ST0929 and SaMTSase active sites were found to be essentially identical. ST0929 also includes the unique tyrosine cluster that encloses the reducing-end glucose subunit in Sulfolobus sp. MTSases. The current structure provides insight into the structural basis of the increase in the hydrolase side reaction that is observed for mutants in which a phenylalanine residue is replaced by a tyrosine residue in the subsite +1 tyrosine cluster of Sulfolobus sp.

Identification of the essential catalytic residues and selectivity-related residues of maltooligosyltrehalose trehalohydrolase from the thermophilic archaeon Sulfolobus solfataricus ATCC 35092

Maltooligosyltrehalose trehalohydrolase (MTHase) catalyzes the release of trehalose by cleaving the alpha-1,4-glucosidic linkage next to the alpha-1,1-linked terminal disaccharide of maltooligosyltrehalose. Mutations at residues D255, E286, and D380 were constructed to identify the essential catalytic residues of MTHase, while mutations at residues W218, A259, Y328, F355, and R356 were constructed to identify selectivity-related residues of the enzyme. The specific activities of the purified D255A, E286A, and D380A MTHases were only 0.15, 0.09 and 0.01%, respectively, of that of wild-type MTHase, suggesting that these three residues are essential catalytic residues. Compared with wild-type MTHase, A259S, Y328F, F355Y, and R356K MTHases had increased selectivity ratios, which were defined as the ratios of the catalytic efficiencies for glucose formation to those for trehalose formation in the hydrolysis of maltooligosaccharides and maltooligosyltrehaloses, respectively, while W218A and W218F MTHases had decreased selectivity ratios. When starch digestion was carried out at 75 degrees C and wild-type and mutant MTHases were, respectively, used with isoamylase and maltooligosyltrehalose synthase (MTSase), the ratios of initial rates of glucose formation to those of trehalose formation were inversely correlated to the peak trehalose yields.

A novel megaprimed and ligase-free, PCR-based, site-directed mutagenesis method

In this study, we report a novel megaprimed and ligase-free, PCR-based, site-directed mutagenesis method modified from the QuikChange site-directed mutagenesis (QCM). One mutagenic oligonucleotide and one universal flanking primer were used to produce the complementary megaprimers that were then used to amplify the whole plasmid template. This method yields a mutagenesis efficiency ( approximately 90%) similar to that of QCM but uses only one mutagenic oligonucleotide instead of two of them, and the length of the oligonucleotide could be shorter. This method can be further extended to double mutations that are located at distant sites by using two mutagenic oligonucleotides and even to site saturation mutagenesis by introducing randomized codons.