A molecular study on recombinant pullulanase type I from Metabacillus indicus

Despite the great potential of cold-adapted pullulanase type I in tremendous industrial applications, the majority of commercialized pullulnases type I are of mesophilic and thermophilic origin so far. Hence, the present study underlines cloning, heterologous expression in Escherichia coli, characterization, and in silico structural modeling of Metabacillus indicus open reading frame of cold-adapted pullulanase type I (Pull_Met: 2133 bp & 710 a.a) for the first time ever. The predicted Pull_Met tertiary structure by I-TASSER, was structurally similar to PDB 2E9B pullulanase of Bacillus subtilis. Purified to homogeneity Pull_Met showed specific activity (667.6 U/mg), fold purification (31.7), molecular mass (79.1 kDa), monomeric subunit and Km (2.63 mg/mL) on pullulan. Pull_Met had optimal pH (6.0) and temperature (40 ^oC). After 10 h pre-incubation at pH 2.6-6.0, Pull_Met maintained 47.12 ± 0.0-35.28 ± 1.64% of its activity. After 120 min pre-incubation at 30 ^oC, the retained activity was 51.11 ± 0.29%. At 10 mM Mn²⁺, Na²⁺, Ca²⁺, Mg²⁺, and Cu²⁺ after 30 min preincubation, retained activity was 155.89 ± 8.97, 134.71 ± 1.82, 97.64 ± 7.06, 92.25 ± 4.18, and 71.28 ± 1.10%, respectively. After 30 min pre-incubation with Tween-80, Tween-20, Triton X-100, and commercially laundry detergents at 0.1% (v/v), the retained activity was 141.15 ± 3.50, 145.45 ± 0.20, 118.12 ± 11.00, and 90%, respectively. Maltotriose was the only end product of pullulan hydrolysis. Synergistic action of CA-AM21 (α-amylase) and Pull_Met on starch liberated 16.51 g reducing sugars /g starch after 1 h at 40 ^oC. Present data (cold-adeptness, detergent stability, and ability to exhibit starch saccharification of Pull_Met) underpins it as a promising pullulanase type I for industrial exploitation.

Improved Stability and Hydrolysates of Hyperthermophilic GH57 Type II Pullulanase from the Deep-Sea Archaeon Thermococcus siculi HJ21 by Truncation

Pullulanase (EC 3.2.1.41) belongs to the amylase family and is often used alone or in combination with other amylases in the industrial production of starch-based products. This enzyme is often required in industrial production because of its better stability. We here truncated the pullulanase gene from the deep-sea hydrothermal anaerobic archaeon Thermococcus siculi HJ21 and obtained Pul-HJΔ782, which is a member of the α-amylase family GH57. The results revealed that the optimum temperature for Pul-HJΔ782 was 100 °C, and its thermostability at 100 °C improved after truncation. Less than 15% of its enzyme activity was lost after 1 h of incubation at 100 °C, and 57% activity remained after 5 h of treatment. Truncation significantly improved the overall pH tolerance range of Pul-HJΔ782, and its stability in the pH range 4–8 was over 80% relative activity from an average of 60%. The sequence and structural model of Pul-HJΔ782 was analyzed, and its instability index was reduced significantly. Furthermore, the hydrolysates of the truncated and wild-type pullulanase were analyzed, and the enzymatic digestion efficiency of the truncated Pul-HJΔ782 was higher.

Characterization of a novel detergent-resistant type I pullulanase from Bacillus megaterium Y103 and its application in laundry detergent

This study aims to find a moderate pullulanase for detergent industry. The pulY103B gene (2217 bp) from Bacillus megaterium Y103 was cloned and expressed in Escherichia coli. PulY103B contained four conserved regions of glycoside hydrolase family (GH) 13 and the typical sequence of type I pullulanase. The optimal reaction conditions of PulY103B were pH 6.5 and 40 °C. In addition, it remained stable below 40 °C and over 80% of activity was retained at pH ranging from 6.0 to 8.5. The best substrate for the enzyme was pullulan. Furthermore, it exhibited activity toward wheat starch (36.5%) and soluble starch (33.4%) but had no activity toward amylose and glycogen. Maltotriose and maltohexaose were major pullulan hydrolysis products. Soluble starch and amylopectin were mainly hydrolyzed into maltotetraose. These results indicated that PulY103B is a novel type I pullulanase with transglycosylation activity via formation of α-1,4-glucosidic linkages. Moreover, PulY103B was strongly stimulated by nonionic detergents [viz, Tween 20 (10%), Tween 80 (1%), Triton X-100 (20%)] and commercial liquid detergents (3.0 g/L). Wash performance tests demonstrated that the mixture of PulY103B and detergent removed starch-based stains better than using detergent alone (p < 0.05). Therefore, this pullulanase has big potential as a detergent additive.

Enhanced Extracellular Production and Characterization of Sucrose Isomerase in Bacillus subtilis with Optimized Signal Peptides

Sucrose isomerase (SIase) catalyzes the hydrolysis and isomerization of sucrose into isomaltulose, which is an important functional sugar widely used in the food industry. However, the lack of safe and efficient expression systems for recombinant SIase has impeded its production and application. In this study, enhanced expression of a SIase from Klebsiella sp. LX3 (referred to as KsLX3-SIase) was achieved in Bacillus subtilis WB800N, by optimizing the signal peptides. First, 13 candidate signal peptides were selected using a semi-rational approach, and their effects on KsLX3-SIase secretion were compared. The signal peptide WapA was most efficient in directing the secretion of KsLX3-SIase into the culture medium, producing a specific activity of 23.0 U/mL, as demonstrated by shake flask culture. Using a fed-batch strategy, the activity of KsLX3-SIase in the culture medium was increased to 125.0 U/mL in a 5-L fermentor. Finally, the expressed KsLX3-SIase was purified and was found to have maximum activity at 45 °C and pH 5.5. Its K_m for sucrose was 267.6 ± 18.6 mmol/L, and its k_cat/K_m was 10.1 ± 0.2 s⁻¹mM⁻¹. These findings demonstrated an efficient expression of SIase in B. subtilis, and this is thought to be the highest level of SIase produced in a food-grade bacteria to date.

Cloning, overexpression, and structural characterization of a novel archaeal thermostable neopullulanase from Desulfurococcus mucosus DSM 2162

The main purpose of the present study is to introduce the biochemical characteristics of the industrial valuable thermostable pullulan degrading enzyme from Desulfurococcus mucosus DSM2162. Recombinant protein was purified by a combination of thermal treatment and affinity chromatography, with a yield of 15.94% and 7.69-fold purity. Purified enzyme showed the molecular mass of 55,787 Da with optimum activity at 70 °C and a broad range of pH (5.0-9.0) with kcat of 2150 min^-1 and Km of 6.55 mg.mL^-1, when using starch as substrate. The enzyme activity assay on various polysaccharide substrates revealed the substrate preference of pullulan > amylopectin > β cyclodextrin > starch > glycogen; therefore, it classified as a neopullulanase. The neopullulanase structural analysis by spectrofluorometer, FT-IR, and circular dichroism spectroscopy indicated the corporation of α-helix (47.3%) and β-sheet (31.6%) in its secondary structure. The melting temperature and specific heat capacity calculations using differential scanning calorimetry confirmed its extreme thermal stability. Further, salt-elevated concentrations resulted in oligomeric state dominancy without any significant influence on the starch-degrading ability. The newly cloned archaeal neopullulanase was with broad activity on polysaccharide substrates, with thermal and salt stability. Thus, the Desulfurococcus mucosus DSM2162 neopullulanase can be introduced as a good candidate to be used in carbohydrate industry.

A Bibliometric Analysis and Review of Pullulan-Degrading Enzymes—Past and Current Trends

Starch and pullulan degrading enzymes are essential industrial biocatalysts. Pullulan-degrading enzymes are grouped into pullulanases (types I and type II) and pullulan hydrolase (types I, II and III). Generally, these enzymes hydrolyse the α-1,6 glucosidic bonds (and α-1,4 for certain enzyme groups) of substrates and form reducing sugars such as glucose, maltose, maltotriose, panose or isopanose. This review covers two main aspects: (i) bibliometric analysis of publications and patents related to pullulan-degrading enzymes and (ii) biological aspects of free and immobilised pullulan-degrading enzymes and protein engineering. The collective data suggest that most publications involved researchers within the same institution or country in the past and current practice. Multi-national interaction shall be improved, especially in tapping the enzymes from unculturable prokaryotes. While the understanding of pullulanases may reach a certain extend of saturation, the discovery of pullulan hydrolases is still limited. In this report, we suggest readers consider using the next-generation sequencing technique to fill the gaps of finding more new sequences encoding pullulan-degrading enzymes to expand the knowledge body of this topic.

Microbial starch debranching enzymes: Developments and applications

Starch debranching enzymes (SDBEs) hydrolyze the α-1,6 glycosidic bonds in polysaccharides such as starch, amylopectin, pullulan and glycogen. SDBEs are also important enzymes for the preparation of sugar syrup, resistant starch and cyclodextrin. As the synergistic catalysis of SDBEs and other starch-acting hydrolases can effectively improve the raw material utilization and production efficiency during starch processing steps such as saccharification and modification, they have attracted substantial research interest in the past decades. The substrate specificities of the two major members of SDBEs, pullulanases and isoamylases, are quite different. Pullulanases generally require at least two α-1,4 linked glucose units existing on both sugar chains linked by the α-1,6 bond, while isoamylases require at least three units of α-1,4 linked glucose. SDBEs mainly belong to glycoside hydrolase (GH) family 13 and 57. Except for GH57 type II pullulanse, GH13 pullulanases and isoamylases share plenty of similarities in sequence and structure of the core catalytic domains. However, the N-terminal domains, which might be one of the determinants contributing to the substrate binding of SDBEs, are distinct in different enzymes. In order to overcome the current defects of SDBEs in catalytic efficiency, thermostability and expression level, great efforts have been made to develop effective enzyme engineering and fermentation strategies. Herein, the diverse biochemical properties and distinct features in the sequence and structure of pullulanase and isoamylase from different sources are summarized. Up-to-date developments in the enzyme engineering, heterologous production and industrial applications of SDBEs is also reviewed. Finally, research perspective which could help understanding and broadening the applications of SDBEs are provided.

Biotechnology and bioengineering of pullulanase: state of the art and perspectives

Pullulanase (EC 3.2.1.41) is a starch-debranching enzyme in the α-amylase family and specifically cleaves α-1,6-glycosidic linkages in starch-type polysaccharides, such as pullulan, β-limited dextrin, glycogen, and amylopectin. It plays a key role in debranching and hydrolyzing starch completely, thus bring improved product quality, increased productivity, and reduced production cost in producing resistant starch, sugar syrup, and beer. Plenty of researches have been made with respects to the discovery of either thermophilic or mesophilic pullulanases, however, few examples meet the demand of industrial application. This review presents the progress made in the recent years from the first aspect of characteristics of pullulanases. The heterologous expression of pullulanases in different microbial hosts and the methods used to improve the expression effectiveness and the regulation of enzyme production are also described. Then, the function evolution of pullulanases from a protein engineering view is discussed. In addition, the immobilization strategy using novel materials is introduced to improve the recyclability of pullulanases. At the same time, we indicate the trends in the future research to facilitate the industrial application of pullulanases.

A novel cold-active type I pullulanase from a hot-spring metagenome for effective debranching and production of resistant starch

Pullulanase is a potent enzyme for starch debranching. In this study, a novel type I pullulanase (Pul_M) was identified from the metagenome of a thermal aquatic habitat that exhibits optimal activity of debranching at 40 °C temperature and pH 6.0 to 7.0. More than 50% enzymatic activity was detected at the low temperature of 4 °C, determining it a cold-active type I pullulanase. It was able to efficiently catalyze the hydrolysis of α-1,6-glycosidic linkages in pullulan, with a specific activity of 177 U mg^-1. The results determined Pul_M to be a potential starch debranching biocatalyst, causing a significant increase of about 80% in the apparent amylose content of potato starch. Retrogradation of the debranched starch resulted in the formation of resistant starch 3. The yield of resistant starch was estimated to be about 45%. The resistant starch exhibited higher crystallinity, enhanced heat-stability, and resistance to α-amylase digestion, as compared to native starch.

Optimizing the DO-stat protocol for enhanced production of thermostable pullulanase in Escherichia coli by using oxygen control strategies

Production of a thermostable pullulanase by DO-stat fed-batch fermentation of recombinant Escherichia coli BL 21 was investigated in a 5 L of fermentor. The effect of three oxygen control strategies, glucose feedback, shifting fermentor pressure, and adding oxygen-enriched air, on cell growth and pullulanase expression were examined. The oxygen-transfer capacity was found to be enhanced with increasing fermentor pressure and oxygen ratio in oxygen-enriched air, but the cell growth and pullulanase production were restrained under high fermentor pressure. The highest cell density and pullulanase activity reached 55.1 g/L and 412 U/mL, respectively, in the case by adding oxygen-enriched air, which was suggested as an effective approach to enhance both cell growth and pullulanase production. PRACTICAL APPLICATIONS: This thermostable pullulanase displayed optimal activity at 90°C and pH 5.4, which could be applied for one-step saccharification of starch biomass. The optimization of the DO-stat fed-batch fermentation in high cell density level would provide a research basis for its industrialization.

N-Terminal Domain Truncation and Domain Insertion-Based Engineering of a Novel Thermostable Type I Pullulanase from Geobacillus thermocatenulatus

A novel thermostable type I pullulanase gene ( pul _GT) from Geobacillus thermocatenulatus DSMZ730 was cloned. It has an open reading frame of 2154 bp encoding 718 amino acids. G. thermocatenulatus pullulanase (Pul_GT) was found to be optimally active at pH 6.5 and 70 °C. It exhibited stable activity in the pH range of 5.5-7.0. Pul_GT lacked three domains (CBM41 domain, X25 domain, and X45 domain) compared with the pullulanase from Bacillus acidopullulyticus ( 2WAN ). Different N-terminally domain truncated (730T) or spliced (730T-U1 and 730T-U2) mutants were constructed. Truncating the N-terminal 85 amino acids decreased the K_m value and did not change its optimum pH, an advantageous biochemical property in some applications. Compared with 2WAN , Pul_GT can be used directly for maize starch saccharification without adjusting the pH, which reduces cost and improves efficiency.