Structure of hyperthermophilic β-glucosidase from Pyrococcus furiosus

Hotspot Wizard-informed engineering of a hyperthermophilic β-glucosidase for enhanced enzyme activity at low temperatures

Hyperthermophilic enzymes serve as an important source of industrial enzymes due to their high thermostability. Unfortunately, most hyperthermophilic enzymes suffer from reduced activity at low temperatures (e.g., ambient temperature), limiting their applicability. In addition, evolving hyperthermophilic enzymes to increase low temperature activity without compromising other desired properties is generally difficult. In the current study, a variant of β-glucosidase from Pyrococcus furiosus (PfBGL) was engineered to enhance enzyme activity at low temperatures through the construction of a saturation mutagenesis library guided by the HotSpot Wizard analysis, followed by its screening for activity and thermostability. From this library construction and screening, one PfBGL mutant, PfBGL-A4 containing Q214S/A264S/F344I mutations, showed an over twofold increase in β-glucosidase activity at 25 and 50°C compared to the wild type, without compromising high-temperature activity, thermostability and substrate specificity. Our experimental and computational characterizations suggest that the findings with PfBGL-A4 may be due to the elevation of local conformational flexibility around the active site, while slightly compacting the global protein structure. This study showcases the potential of HotSpot Wizard-informed engineering of hyperthermophilic enzymes and underscores the interplays among temperature, enzyme activity, and conformational flexibility in these enzymes.

The archaeal highly thermostable GH35 family β-galactosidase DaβGal has a unique seven domain protein fold

The most extensively studied β-d-galactosidases (EC3.2.1.23) belonging to four glycoside hydrolase (GH) families 1, 2, 35, and 42 are widely distributed among Bacteria, Archaea and Eukaryotes. Here, we report a novel GH35 family β-galactosidase from the hyperthermophilic Thermoprotei archaeon Desulfurococcus amylolyticus (DaβGal). Unlike fungal monomeric six-domain β-galactosidases, the DaβGal enzyme is a dimer; it has an extra jelly roll domain D7 and three composite domains (D4, D5, and D6) that are formed by the distantly located polypeptide chain regions. The enzyme possesses a high specificity for β-d-galactopyranosides, and its distinguishing feature is the ability to cleave pNP-β-d-fucopyranoside. DaβGal efficiently catalyzes the hydrolysis of lactose at high temperatures, remains stable and active at 65 °С, and retains activity at 95 °С with a half-life time value equal to 73 min. These properties make archaeal DaβGal a more attractive candidate for biotechnology than the widely used fungal β-galactosidases.

Exploring the diversity of β-glucosidase: Classification, catalytic mechanism, molecular characteristics, kinetic models, and applications

High-value chemicals and energy-related products can be produced from biomass. Biorefinery technology offers a sustainable and cost-effective method for this high-value conversion. β-glucosidase is one of the key enzymes in biorefinery processes, catalyzing the production of glucose from aryl-glycosides and cello-oligosaccharides via the hydrolysis of β-glycosidic bonds. Although β-glucosidase plays a critical catalytic role in the utilization of cellulosic biomass, its efficacy is often limited by substrate or product inhibitions, low thermostability, and/or insufficient catalytic activity. To provide a detailed overview of β-glucosidases and their benefits in certain desired applications, we collected and summarized extensive information from literature and public databases, covering β-glucosidases in different glycosidase hydrolase families and biological kingdoms. These β-glucosidases show differences in amino acid sequence, which are translated into varying degrees of the molecular properties critical in enzymatic applications. This review describes studies on the diversity of β-glucosidases related to the classification, catalytic mechanisms, key molecular characteristics, kinetics models, and applications, and highlights several β-glucosidases displaying high stability, activity, and resistance to glucose inhibition suitable for desired biotechnological applications.

Identification and function of an Arasin-like peptide from Litopenaeus vannamei

Antimicrobial peptides (AMPs) play an important role in the host defense system of shrimps. In this study, an Arasin-like peptide, named as LvArasin-like, was identified from the hemocytes of the pacific white shrimp, Litopenaeus vannamei. The complete open reading frame (ORF) of LvArasin-like was 213 bp, encoding 70 amino acid residues with a predicted molecular mass of 5.68 kDa and a theoretical isoelectric point (pI) of 6.73. The predicted peptide consisted of a signal peptide, an N-terminal Pro/Arg-rich domain, and a C-terminal cysteine-rich domain. LvArasin-like expression was most abundant in the gills and was up-regulated in hemocytes after LPS or Poly I:C injection as well as challenges by Vibrio parahaemolyticus or Staphylococcus aureus infection. In the heterologous expression system, LvArasin-like protein (rLvArasin-like) was recombinantly expressed in the forms of a dimer or both a monomer and dimer. The rLvArasin-like could directly bind to gram-positive and gram-negative bacteria and exhibited broad-spectrum antimicrobial activity towards them, with 50 % of minimal inhibitory concentrations (MIC50) of 6.25-50 μM. Moreover, dsRNA-mediated knockdown of LvArasin-like enhanced the susceptibility of shrimp to V. parahaemolyticus. In addition, the transcriptional level of LvArasin-like was downregulated when silencing of the transcription factors LvDorsal and LvRelish using RNAi in vivo. All of these results suggest that LvArasin-like is involved in host defense against bacterial infection. Therefore, it is a potential therapeutic agent for disease control in shrimp aquaculture.

Glycoside Hydrolases and Glycosyltransferases from Hyperthermophilic Archaea: Insights on Their Characteristics and Applications in Biotechnology

Hyperthermophilic Archaea colonizing unnatural habitats of extremes conditions such as volcanoes and deep-sea hydrothermal vents represent an unmeasurable bioresource for enzymes used in various industrial applications. Their enzymes show distinct structural and functional properties and are resistant to extreme conditions of temperature and pressure where their mesophilic homologs fail. In this review, we will outline carbohydrate-active enzymes (CAZymes) from hyperthermophilic Archaea with specific focus on the two largest families, glycoside hydrolases (GHs) and glycosyltransferases (GTs). We will present the latest advances on these enzymes particularly in the light of novel accumulating data from genomics and metagenomics sequencing technologies. We will discuss the contribution of these enzymes from hyperthermophilic Archaea to industrial applications and put the emphasis on newly identifed enzymes. We will highlight their common biochemical and distinct features. Finally, we will overview the areas that remain to be explored to identify novel promising hyperthermozymes.

Coexpression of a β-d-Xylosidase from Thermotoga maritima and a Family 10 Xylanase from Acidothermus cellulolyticus Significantly Improves the Xylan Degradation Activity of the Caldicellulosiruptor bescii Exoproteome

Caldicellulosiruptor species are hyperthermophilic, Gram-positive anaerobes and the most thermophilic cellulolytic bacteria so far described. They have been engineered to convert switchgrass to ethanol without pretreatment and represent a promising platform for the production of fuels, chemicals, and materials from plant biomass. Xylooligomers, such as xylobiose and xylotriose, that result from the breakdown of plant biomass more strongly inhibit cellulase activity than do glucose or cellobiose. High concentrations of xylobiose and xylotriose are present in C. bescii fermentations after 90 h of incubation, and removal or breakdown of these types of xylooligomers is crucial to achieving high conversion of plant biomass to product. In previous studies, the addition of exogenous β-d-xylosidase substantially improved the performance of glucanases and xylanases in vitro. β-d-Xylosidases are, in fact, essential enzymes in commercial preparations for efficient deconstruction of plant biomass. In addition, the combination of xylanase and β-d-xylosidase is known to exhibit synergistic action on xylan degradation. In spite of its ability to grow efficiently on xylan substrates, no extracellular β-d-xylosidase was identified in the C. bescii genome. Here, we report that the coexpression of a thermal stable β-d-xylosidase from Thermotoga maritima and a xylanase from Acidothermus cellulolyticus in a C. bescii strain containing the A. cellulolyticus E1 endoglucanase significantly increased the activity of the exoproteome as well as growth on xylan substrates. The combination of these enzymes also resulted in increased growth on crystalline cellulose in the presence of exogenous xylan. IMPORTANCE Caldicellulosiruptor species are bacteria that grow at extremely high temperature, more than 75°C, and are the most thermophilic bacteria so far described that are capable of growth on plant biomass. This native ability allows the use of unpretreated biomass as a growth substrate, eliminating the prohibitive cost of preprocessing/pretreatment of the biomass. They only grow under strictly anaerobic conditions, and the combination of high temperature and the lack of oxygen reduces the cost of fermentation and contamination by other microbes. They have been genetically engineered to convert switchgrass to ethanol without pretreatment and represent a promising platform for the production of fuels, chemicals, and materials from plant biomass. In this study, we introduced genes from other cellulolytic bacteria and identified a combination of enzymes that improves growth on plant biomass. An important feature of this study is that it measures growth, validating predictions made from adding enzyme mixtures to biomass.

Optimal secretion of thermostable Beta-glucosidase in Bacillus subtilis by signal peptide optimization

Commercial applications of β-glucosidase (BGL) demands its purity and availability on a large scale. In the present study, we aim to optimize the expression and secretion of a thermostable BGL from Pyrococcus furiosus (PfuBGL) in B. subtilis strain RIK1285. Initial studies with base strain BV002 harboring aprE signal peptide (aprESP) showed PfuBGL yield of 0.743 ± 0.19 pNP U/ml only. A library of 173 different homologous SPs from B. subtilis 168 genome was fused with target PfuBGL gene (PF0073) in pBE-S vector and extracellularly expressed in RIK1285 strain to identify optimal SP for PfuBGL secretion. High-throughput screening of the resulting SP library for BGL activity with a synthetic substrate followed by systematic scaling of the clones yielded a gene construct with CitHSP reporting a sixteen fold enhancement of PfuBGL secretion in comparison to base strain. Batch fermentation (7.5 L scale) PfuBGL yield of the BV003 strain with CitHSP-PF0073 fusion was observed to be 12.08 ± 0.21 pNP U/ml with specific activity of 35.52 ± 0.53 U/mg. Thus, the study represents report on the secretory expression of thermostable PfuBGL using B. subtilis as a host organism and demonstrating its high potential for industrial production of any protein/enzyme.

A microalgal-based preparation with synergistic cellulolytic and detoxifying action towards chemical-treated lignocellulose

High-temperature bioconversion of lignocellulose into fermentable sugars has drawn attention for efficient production of renewable chemicals and biofuels, because competing microbial activities are inhibited at elevated temperatures and thermostable cell wall degrading enzymes are superior to mesophilic enzymes. Here, we report on the development of a platform to produce four different thermostable cell wall degrading enzymes in the chloroplast of Chlamydomonas reinhardtii. The enzyme blend was composed of the cellobiohydrolase CBM3GH5 from C. saccharolyticus, the β-glucosidase celB from P. furiosus, the endoglucanase B and the endoxylanase XynA from T. neapolitana. In addition, transplastomic microalgae were engineered for the expression of phosphite dehydrogenase D from Pseudomonas stutzeri, allowing for growth in non-axenic media by selective phosphite nutrition. The cellulolytic blend composed of the glycoside hydrolase (GH) domain GH12/GH5/GH1 allowed the conversion of alkaline-treated lignocellulose into glucose with efficiencies ranging from 14% to 17% upon 48h of reaction and an enzyme loading of 0.05% (w/w). Hydrolysates from treated cellulosic materials with extracts of transgenic microalgae boosted both the biogas production by methanogenic bacteria and the mixotrophic growth of the oleaginous microalga Chlorella vulgaris. Notably, microalgal treatment suppressed the detrimental effect of inhibitory by-products released from the alkaline treatment of biomass, thus allowing for efficient assimilation of lignocellulose-derived sugars by C. vulgaris under mixotrophic growth.

Homodimerization of a glycoside hydrolase family GH1 β-glucosidase suggests distinct activity of enzyme different states

In this work, we investigated how activity and oligomeric state are related in a purified GH1 β-glucosidase from Spodoptera frugiperda (Sfβgly). Gel filtration chromatography coupled to a multiple angle light scattering detector allowed separation of the homodimer and monomer states and determination of the dimer dissociation constant (K_D ), which was in the micromolar range. Enzyme kinetic parameters showed that the dimer is on average 2.5-fold more active. Later, we evaluated the kinetics of homodimerization, scanning the changes in the Sfβgly intrinsic fluorescence over time when the dimer dissociates into the monomer after a large dilution. We described how the rate constant of monomerization (k_off ) is affected by temperature, revealing the enthalpic and entropic contributions to the process. We also evaluated how the rate constant (k_obs ) by which equilibrium is reached after dimer dilution behaves when varying the initial Sfβgly concentration. These data indicated that Sfβgly dimerizes through the conformational selection mechanism, in which the monomer undergoes a conformational exchange and then binds to a similar monomer, forming a more active homodimer. Finally, we noted that conformational selection reports and experiments usually rely on a ligand whose concentration is in excess, but for homodimerization, this approach does not hold. Hence, since our approach overcomes this limitation, this study not only is a new contribution to the comprehension of GH1 β-glucosidases, but it can also help to elucidate protein interaction pathways.

N-terminal domain replacement changes an archaeal monoacylglycerol lipase into a triacylglycerol lipase

BACKGROUND

Lipolytic enzymes of hyperthermophilic archaea generally prefer small carbon chain fatty acid esters (C₂-C₁₂) and are categorized as esterases. However, a few have shown activity with long-chain fatty acid esters, but none of them have been classified as a true lipase except a lipolytic enzyme AFL from Archaeglobus fulgidus. Thus, our main objective is to engineer an archaeal esterase into a true thermostable lipase for industrial applications. Lipases which hydrolyze long-chain fatty acid esters display an interfacial activation mediated by the lid domain which lies over active site and switches to open conformation at the oil-water interface. Lid domains modulate enzyme activities, substrate specificities, and stabilities which have been shown by protein engineering and mutational analyses. Here, we report engineering of an uncharacterized monoacylglycerol lipase (TON-LPL) from an archaeon Thermococcus onnurineus (strain NA1) into a triacylglycerol lipase (rc-TGL) by replacing its 61 N-terminus amino acid residues with 118 residues carrying lid domain of a thermophilic fungal lipase-Thermomyces lanuginosus (TLIP).

RESULTS

TON-LPL and rc-TGL were cloned and overexpressed in E. coli, and the proteins were purified by Ni-NTA affinity chromatography for biochemical studies. Both enzymes were capable of hydrolyzing various monoglycerides and shared the same optimum pH of 7.0. However, rc-TGL showed a significant decrease of 10 °C in its optimum temperature (T_opt). The far UV-CD spectrums were consistent with a well-folded α/β-hydrolase fold for both proteins, but gel filtration chromatography revealed a change in quaternary structure from trimer (TON-LPL) to monomer (rc-TGL). Seemingly, the difference in the oligomeric state of rc-TGL may be linked to a decrease in temperature optimum. Nonetheless, rc-TGL hydrolyzed triglycerides and castor oil, while TON-LPL was not active with these substrates.

CONCLUSIONS

Here, we have confirmed the predicted esterase activity of TON-LPL and also performed the lid engineering on TON-LPL which effectively expanded its substrate specificity from monoglycerides to triglycerides. This approach provides a way to engineer other hyperthermophilic esterases into industrially suitable lipases by employing N-terminal domain replacement. The immobilized preparation of rc-TGL has shown significant activity with castor oil and has a potential application in castor oil biorefinery to obtain value-added chemicals.

Expression of a Cellobiose Phosphorylase from Thermotoga maritima in Caldicellulosiruptor bescii Improves the Phosphorolytic Pathway and Results in a Dramatic Increase in Cellulolytic Activity

Members of the genus Caldicellulosiruptor have the ability to deconstruct and grow on lignocellulosic biomass without conventional pretreatment. A genetically tractable species, Caldicellulosiruptor bescii, was recently engineered to produce ethanol directly from switchgrass. C. bescii contains more than 50 glycosyl hydrolases and a suite of extracellular enzymes for biomass deconstruction, most prominently CelA, a multidomain cellulase that uses a novel mechanism to deconstruct plant biomass. Accumulation of cellobiose, a product of CelA during growth on biomass, inhibits cellulase activity. Here, we show that heterologous expression of a cellobiose phosphorylase from Thermotoga maritima improves the phosphorolytic pathway in C. bescii and results in synergistic activity with endogenous enzymes, including CelA, to increase cellulolytic activity and growth on crystalline cellulose.IMPORTANCE CelA is the only known cellulase to function well on highly crystalline cellulose and it uses a mechanism distinct from those of other cellulases, including fungal cellulases. Also unlike fungal cellulases, it functions at high temperature and, in fact, outperforms commercial cellulase cocktails. Factors that inhibit CelA during biomass deconstruction are significantly different than those that impact the performance of fungal cellulases and commercial mixtures. This work contributes to understanding of cellulase inhibition and enzyme function and will suggest a rational approach to engineering optimal activity.

Heterologous expression of a β-D-glucosidase in Caldicellulosiruptor bescii has a surprisingly modest effect on the activity of the exoproteome and growth on crystalline cellulose

Members of the genus Caldicellulosiruptor are the most thermophilic cellulolytic bacteria so far described and are capable of efficiently utilizing complex lignocellulosic biomass without conventional pretreatment. Previous studies have shown that accumulation of high concentrations of cellobiose and, to a lesser extent, cellotriose, inhibits cellulase activity both in vivo and in vitro and high concentrations of cellobiose are present in C. bescii fermentations after 90 h of incubation. For some cellulolytic microorganisms, β-D-glucosidase is essential for the efficient utilization of cellobiose as a carbon source and is an essential enzyme in commercial preparations for efficient deconstruction of plant biomass. In spite of its ability to grow efficiently on crystalline cellulose, no extracellular β-D-glucosidase or its GH1 catalytic domain could be identified in the C. bescii genome. To investigate whether the addition of a secreted β-D-glucosidase would improve growth and cellulose utilization by C. bescii, we cloned and expressed a thermostable β-D-glucosidase from Acidothermus cellulolyticus (Acel_0133) in C. bescii using the CelA signal sequence for protein export. The effect of this addition was modest, suggesting that β-D-glucosidase is not rate limiting for cellulose deconstruction and utilization by C. bescii.

Systematic studies of the interactions between a model polyphenol compound and microbial β-glucosidases

Lignin is a major obstacle for cost-effective conversion of cellulose into fermentable sugars. Non-productive adsorption onto insoluble lignin fragments and interactions with soluble phenols are important inhibition mechanisms of cellulases, including β-glucosidases. Here, we examined the inhibitory effect of tannic acid (TAN), a model polyphenolic compound, on β-glucosidases from the bacterium Thermotoga petrophila (TpBGL1 and TpBGL3) and archaeon Pyrococcus furiosus (PfBGL1). The results revealed that the inhibition effects on β-glucosidases were TAN concentration-dependent. TpBGL1 and TpBGL3 were more tolerant to the presence of TAN when compared with PfBGL1, while TpBGL1 was less inhibited when compared with TpBGL3. In an attempt to better understand the inhibitory effect, the interaction between TAN and β-glucosidases were analyzed by isothermal titration calorimetry (ITC). Furthermore, the exposed hydrophobic surface areas in β-glucosidases were analyzed using a fluorescent probe and compared with the results of inhibition and ITC. The binding constants determined by ITC for the interactions between TAN and β-glucosidases presented the same order of magnitude. However, the number of binding sites and exposed hydrophobic surface areas varied for the β-glucosidases studied. The binding between TAN and β-glucosidases were driven by enthalpic effects and with an unfavorable negative change in entropy upon binding. Furthermore, the data suggest that there is a high correlation between exposed hydrophobic surface areas and the number of binding sites on the inhibition of microbial β-glucosidases by TAN. These studies can be useful for biotechnological applications.

Cargo-shell and cargo-cargo couplings govern the mechanics of artificially loaded virus-derived cages

Nucleic acids are the natural cargo of viruses and key determinants that affect viral shell stability. In some cases the genome structurally reinforces the shell, whereas in others genome packaging causes internal pressure that can induce destabilization. Although it is possible to pack heterologous cargoes inside virus-derived shells, little is known about the physical determinants of these artificial nanocontainers' stability. Atomic force and three-dimensional cryo-electron microscopy provided mechanical and structural information about the physical mechanisms of viral cage stabilization beyond the mere presence/absence of cargos. We analyzed the effects of cargo-shell and cargo-cargo interactions on shell stability after encapsulating two types of proteinaceous payloads. While bound cargo to the inner capsid surface mechanically reinforced the capsid in a structural manner, unbound cargo diffusing freely within the shell cavity pressurized the cages up to ∼30 atm due to steric effects. Strong cargo-cargo coupling reduces the resilience of these nanocompartments in ∼20% when bound to the shell. Understanding the stability of artificially loaded nanocages will help to design more robust and durable molecular nanocontainers.

Oligomeric state and structural stability of two hyperthermophilic β-glucosidases from Thermotoga petrophila

The β-glucosidases are enzymes essential for several industrial applications, especially in the field of plant structural polysaccharides conversion into bioenergy and bioproducts. In a recent study, we have provided a biochemical characterization of two hyperthermostable β-glucosidases from Thermotoga petrophila belonging to the families GH1 (TpBGL1) and GH3 (TpBGL3). Here, as part of a continuing investigation, the oligomeric state, the net charge, and the structural stability, at acidic pH, of the TpBGL1 and TpBGL3 were characterized and compared. Enzymatic activity is directly related to the balance between protonation and conformational changes. Interestingly, our results indicated that there were no significant changes in the secondary, tertiary and quaternary structures of the β-glucosidases at temperatures below 80 °C. Furthermore, the results indicated that both the enzymes are stable homodimers in solution. Therefore, the observed changes in the enzymatic activities are due to variations in pH that modify protonation of the enzymes residues and the net charge, directly affecting the interactions with ligands. Finally, the results showed that the two β-glucosidases displayed different pH dependence of thermostability at temperatures above 80 °C. TpBGL1 showed higher stability at pH 6 than at pH 4, while TpBGL3 showed similar stability at both pH values. This study provides a useful comparison of the structural stability, at acidic pH, of two different hyperthermostable β-glucosidases and how it correlates with the activity of the enzymes. The information described here can be useful for biotechnological applications in the biofuel and food industries.

Monomer structure of a hyperthermophilic β-glucosidase mutant forming a dodecameric structure in the crystal form

A protein-engineering study revealed that the C-terminal domain of a thermostable β-glucosidase contributes to its polymeric state.

One of the β-glucosidases from Pyrococcus furiosus (BGLPf) is found to be a hyperthermophilic tetrameric enzyme that can degrade cellooligosaccharides. Recently, the crystal structures of the tetrameric and dimeric forms were solved. Here, a new monomeric form of BGLPf was constructed by removing the C-terminal region of the enzyme and its crystal structure was solved at a resolution of 2.8 Å in space group P1. It was discovered that the mutant enzyme forms a unique dodecameric structure consisting of two hexameric rings in the asymmetric unit of the crystal. Under biological conditions, the mutant enzyme forms a monomer. This result helps explain how BGLPf has attained its oligomeric structure and thermostability.

An intermolecular disulfide bond is required for thermostability and thermoactivity of β-glycosidase from Thermococcus kodakarensis KOD1

Scientists are interested in understanding the molecular origin of protein thermostability and thermoactivity for possible biotechnological applications. The enzymes from extremophilic organisms have been of particular interest in the last two decades. β-glycosidase, Tkβgly is a hyperthermophilic enzyme from Thermococcus kodakarensis KOD1. Tkβgly contains two conserved cysteine residues, C88 and C376. The protein tertiary structure obtained through homology modeling suggests that the C88 residue is located on the surface whereas C376 is inside the protein. To study the role of these cysteine residues, we substituted C88 and C376 with serine residues through site-directed mutagenesis. The wild-type and C376S protein existed in dimeric form and C88S in monomeric form, in an SDS-PAGE gel under non-reducing conditions. Optimal temperature experiments revealed that the wild-type was active at 100 °C whereas the C88S mutant exhibited optimal activity at 70 °C. The half-life of the enzyme at 70 °C was drastically reduced from 266 h to less than 1 h. Although C88 was not present in the active site region, the kcat/Km of C88S was reduced by 2-fold. Based on the structural model and biochemical properties, we propose that C88 is crucial in maintaining the thermostability and thermoactivity of the Tkβgly enzyme.

Structural analysis of β-glucosidase mutants derived from a hyperthermophilic tetrameric structure

Substitutive mutations that convert a tetrameric β-glucosidase into a dimeric state lead to improvement of its crystal quality.

β-Glucosidase from Pyrococcus furiosus (BGLPf) is a hyperthermophilic tetrameric enzyme which can degrade cellooligosaccharides to glucose under hyperthermophilic conditions and thus holds promise for the saccharification of lignocellulosic biomass at high temperature. Prior to the production of large amounts of this enzyme, detailed information regarding the oligomeric structure of the enzyme is required. Several crystals of BGLPf have been prepared over the past ten years, but its crystal structure had not been solved until recently. In 2011, the first crystal structure of BGLPf was solved and a model was constructed at somewhat low resolution (2.35 Å). In order to obtain more detailed structural data on BGLPf, the relationship between its tetrameric structure and the quality of the crystal was re-examined. A dimeric form of BGLPf was constructed and its crystal structure was solved at a resolution of 1.70 Å using protein-engineering methods. Furthermore, using the high-resolution crystal structural data for the dimeric form, a monomeric form of BGLPf was constructed which retained the intrinsic activity of the tetrameric form. The thermostability of BGLPf is affected by its oligomeric structure. Here, the biophysical and biochemical properties of engineered dimeric and monomeric BGLPfs are reported, which are promising prototype models to apply to the saccharification reaction. Furthermore, details regarding the oligomeric structures of BGLPf and the reasons why the mutations yielded improved crystal structures are discussed.