1
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de Lima MZT, de Almeida LR, Mera AM, Bernardes A, Garcia W, Muniz JRC. Crystal Structure of a Sucrose-6-phosphate Hydrolase from Lactobacillus gasseri with Potential Applications in Fructan Production and the Food Industry. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2021; 69:10223-10234. [PMID: 34449216 DOI: 10.1021/acs.jafc.1c03901] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Fructooligosaccharides (FOSs) are polymers of fructose with a prebiotic activity because of their production and fermentation by bacteria that inhabit the gastrointestinal tract and are widely used in the industry and new functional foods. Lactobacillus gasseri stands out as an important homofermentative microorganism related to FOS production, and its potential applications in the industry are undeniable. In this study, we report the production and characterization of a sucrose-6-phosphate hydrolase from L. gasseri belonging to the GH32 family. Apo-LgAs32 and LgAs32 complexed with β-d-fructose structures were determined at a resolution of 1.94 and 1.84 Å, respectively. The production of FOS, fructans, 1-kestose, and nystose by the recombinant LgAs32, using sucrose as a substrate, shown in this study is very promising. When compared to its homologous enzyme from Lactobacillus reuteri, the production of 1-kestose by LgAs32 is increased; thus, LgAs32 can be considered as an alternative in fructan production and other industrial applications.
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Affiliation(s)
- Mariana Z T de Lima
- Sao Carlos Institute of Physics (IFSC), University of Sao Paulo (USP), Sao Carlos, SP 13563-120, Brazil
| | - Leonardo R de Almeida
- Sao Carlos Institute of Physics (IFSC), University of Sao Paulo (USP), Sao Carlos, SP 13563-120, Brazil
| | - Alain M Mera
- Sao Carlos Institute of Physics (IFSC), University of Sao Paulo (USP), Sao Carlos, SP 13563-120, Brazil
| | - Amanda Bernardes
- Sao Carlos Institute of Physics (IFSC), University of Sao Paulo (USP), Sao Carlos, SP 13563-120, Brazil
| | - Wanius Garcia
- Centro de Ciências Naturais e Humanas (CCNH), Universidade Federal do ABC (UFABC), Santo André, SP 09210-580, Brazil
| | - João R C Muniz
- Sao Carlos Institute of Physics (IFSC), University of Sao Paulo (USP), Sao Carlos, SP 13563-120, Brazil
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2
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Thermostable cellulose saccharifying microbial enzymes: Characteristics, recent advances and biotechnological applications. Int J Biol Macromol 2021; 188:226-244. [PMID: 34371052 DOI: 10.1016/j.ijbiomac.2021.08.024] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Revised: 07/19/2021] [Accepted: 08/03/2021] [Indexed: 12/12/2022]
Abstract
Cellulases play a promising role in the bioconversion of renewable lignocellulosic biomass into fermentable sugars which are subsequently fermented to biofuels and other value-added chemicals. Besides biofuel industries, they are also in huge demand in textile, detergent, and paper and pulp industries. Low titres of cellulase production and processing are the main issues that contribute to high enzyme cost. The success of ethanol-based biorefinery depends on high production titres and the catalytic efficiency of cellulases functional at elevated temperatures with acid/alkali tolerance and the low cost. In view of their wider application in various industrial processes, stable cellulases that are active at elevated temperatures in the acidic-alkaline pH ranges, and organic solvents and salt tolerance would be useful. This review provides a recent update on the advances made in thermostable cellulases. Developments in their sources, characteristics and mechanisms are updated. Various methods such as rational design, directed evolution, synthetic & system biology and immobilization techniques adopted in evolving cellulases with ameliorated thermostability and characteristics are also discussed. The wide range of applications of thermostable cellulases in various industrial sectors is described.
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3
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Ibrahim E, Mahmoud A, Jones KD, Taylor KE, Hosseney EN, Mills PL, Escudero JM. Kinetics and thermodynamics of thermal inactivation for recombinant Escherichia coli cellulases, cel12B, cel8C, and polygalacturonase, peh28; biocatalysts for biofuel precursor production. J Biochem 2021; 169:109-117. [PMID: 32810224 DOI: 10.1093/jb/mvaa097] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 08/11/2020] [Indexed: 11/13/2022] Open
Abstract
Lignocellulosic biomass conversion using cellulases/polygalacturonases is a process that can be progressively influenced by several determinants involved in cellulose microfibril degradation. This article focuses on the kinetics and thermodynamics of thermal inactivation of recombinant Escherichia coli cellulases, cel12B, cel8C and a polygalacturonase, peh 28, derived from Pectobacterium carotovorum sub sp. carotovorum. Several consensus motifs conferring the enzymes' thermal stability in both cel12B and peh28 model structures have been detailed earlier, which were confirmed for the three enzymes through the current study of their thermal inactivation profiles over the 20-80°C range using the respective activities on carboxymethylcellulose and polygalacturonic acid. Kinetic constants and half-lives of thermal inactivation, inactivation energy, plus inactivation entropies, enthalpies and Gibbs free energies, revealed high stability, less conformational change and protein unfolding for cel12B and peh28 due to thermal denaturation compared to cel8C. The apparent thermal stability of peh28 and cel12B, along with their hydrolytic efficiency on a lignocellulosic biomass conversion as reported previously, makes these enzymes candidates for various industrial applications. Analysis of the Gibbs free energy values suggests that the thermal stabilities of cel12B and peh28 are entropy-controlled over the tested temperature range.
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Affiliation(s)
- Eman Ibrahim
- Department of Environmental Engineering, Texas A&M University-Kingsville, Kingsville, TX 78363, USA.,Department of Botany and Microbiology, Al-Azhar University, Nasr City, Cairo 11884, Egypt
| | - Ahmed Mahmoud
- Department of Environmental Engineering, Texas A&M University-Kingsville, Kingsville, TX 78363, USA
| | - Kim D Jones
- Department of Environmental Engineering, Texas A&M University-Kingsville, Kingsville, TX 78363, USA
| | - Keith E Taylor
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
| | - Ebtesam N Hosseney
- Department of Botany and Microbiology, Al-Azhar University, Nasr City, Cairo 11884, Egypt
| | - Patrick L Mills
- Department of Chemical Engineering, Texas A&M University-Kingsville, Kingsville, TX 78363, USA
| | - Jean M Escudero
- Department of Basic Sciences, St. Louis College of Pharmacy, St. Louis, MO 63110-1088, USA
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4
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da Silva VM, Cabral AD, Sperança MA, Squina FM, Muniz JRC, Martin L, Nicolet Y, Garcia W. High-resolution structure of a modular hyperthermostable endo-β-1,4-mannanase from Thermotoga petrophila: The ancillary immunoglobulin-like module is a thermostabilizing domain. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2020; 1868:140437. [PMID: 32325255 DOI: 10.1016/j.bbapap.2020.140437] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 03/20/2020] [Accepted: 04/18/2020] [Indexed: 11/16/2022]
Abstract
The endo-β-1,4-mannanase from the hyperthermostable bacterium Thermotoga petrophila (TpMan) is an enzyme that catalyzes the hydrolysis of mannan and heteromannan polysaccharides. Of the three domains that comprise TpMan, the N-terminal GH5 catalytic domain and the C-terminal carbohydrate-binding domain are connected through a central ancillary domain of unknown structure and function. In this study, we report the partial crystal structure of the TpMan at 1.45 Å resolution, so far, the first modular hyperthermostable endo-β-1,4-mannanase structure determined. The structure exhibits two domains, a (β/α)8-barrel GH5 catalytic domain connected via a linker to the central domain with an immunoglobulin-like β-sandwich fold formed of seven β-strands. Functional analysis showed that whereas the immunoglobulin-like domain does not have the carbohydrate-binding function, it stacks on the GH5 catalytic domain acting as a thermostabilizing domain and allowing operation at hyperthermophilic conditions. The carbohydrate-binding domain is absent in the crystal structure most likely due to its high flexibility around the immunoglobulin-like domain which may act also as a pivot. These results represent new structural and functional information useful on biotechnological applications for biofuel and food industries.
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Affiliation(s)
- Viviam M da Silva
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, SP, Brazil; Univ. Grenoble Alpes, CEA, CNRS, IBS, Metalloproteins Unit, F-38000 Grenoble, France
| | - Aline D Cabral
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), São Bernardo do Campo, SP, Brazil
| | - Marcia A Sperança
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), São Bernardo do Campo, SP, Brazil
| | - Fabio M Squina
- Programa de Processos Tecnológicos e Ambientais, Universidade de Sorocaba (UNISO), Sorocaba, SP, Brazil
| | - João Renato C Muniz
- São Carlos Institute of Physics (IFSC), University of São Paulo (USP), São Carlos, SP, Brazil
| | - Lydie Martin
- Univ. Grenoble Alpes, CEA, CNRS, IBS, Metalloproteins Unit, F-38000 Grenoble, France
| | - Yvain Nicolet
- Univ. Grenoble Alpes, CEA, CNRS, IBS, Metalloproteins Unit, F-38000 Grenoble, France
| | - Wanius Garcia
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, SP, Brazil.
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5
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A biochemical comparison of fungal GH6 cellobiohydrolases. Biochem J 2019; 476:2157-2172. [DOI: 10.1042/bcj20190185] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Revised: 07/14/2019] [Accepted: 07/16/2019] [Indexed: 02/02/2023]
Abstract
AbstractCellobiohydrolases (CBHs) from glycoside hydrolase family 6 (GH6) make up an important part of the secretome in many cellulolytic fungi. They are also of technical interest, particularly because they are part of the enzyme cocktails that are used for the industrial breakdown of lignocellulosic biomass. Nevertheless, functional studies of GH6 CBHs are scarce and focused on a few model enzymes. To elucidate functional breadth among GH6 CBHs, we conducted a comparative biochemical study of seven GH6 CBHs originating from fungi living in different habitats, in addition to one enzyme variant. The enzyme sequences were investigated by phylogenetic analyses to ensure that they were not closely related phylogenetically. The selected enzymes were all heterologously expressed in Aspergillus oryzae, purified and thoroughly characterized biochemically. This approach allowed direct comparisons of functional data, and the results revealed substantial variability. For example, the adsorption capacity on cellulose spanned two orders of magnitude and kinetic parameters, derived from two independent steady-state methods also varied significantly. While the different functional parameters covered wide ranges, they were not independent since they changed in parallel between two poles. One pole was characterized by strong substrate interactions, high adsorption capacity and low turnover number while the other showed weak substrate interactions, poor adsorption and high turnover. The investigated enzymes essentially defined a continuum between these two opposites, and this scaling of functional parameters raises interesting questions regarding functional plasticity and evolution of GH6 CBHs.
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6
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Low-resolution structure, oligomerization and its role on the enzymatic activity of a sucrose-6-phosphate hydrolase from Bacillus licheniformis. Amino Acids 2019; 51:599-610. [DOI: 10.1007/s00726-018-02690-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2018] [Accepted: 12/17/2018] [Indexed: 11/25/2022]
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7
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Ezaki T, Nishinari K, Samejima M, Igarashi K. Bridging the Micro-Macro Gap between Single-Molecular Behavior and Bulk Hydrolysis Properties of Cellulase. PHYSICAL REVIEW LETTERS 2019; 122:098102. [PMID: 30932525 DOI: 10.1103/physrevlett.122.098102] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Revised: 12/07/2018] [Indexed: 06/09/2023]
Abstract
The microscopic kinetics of enzymes at the single-molecule level often deviate considerably from those expected from bulk biochemical experiments. Here, we propose a coarse-grained-model approach to bridge this gap, focusing on the unexpectedly slow bulk hydrolysis of crystalline cellulose by cellulase, which constitutes a major obstacle to mass production of biofuels and biochemicals. Building on our previous success in tracking the movements of single molecules of cellulase on crystalline cellulose, we develop a mathematical description of the collective motion and function of enzyme molecules hydrolyzing the surface of cellulose. Model simulations robustly explained the experimental findings at both the microscopic and macroscopic levels and revealed a hitherto-unknown mechanism causing a considerable slowdown of the reaction, which we call the crowding-out effect. The size of the cellulase molecule impacted significantly on the collective dynamics, whereas the rate of molecular motion on the surface did not.
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Affiliation(s)
- Takahiro Ezaki
- Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
- Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Katsuhiro Nishinari
- Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
| | - Masahiro Samejima
- Department of Biomaterial Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Kiyohiko Igarashi
- Department of Biomaterial Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
- VTT Technical Research Centre of Finland, Tietotie 2, Espoo FI-02044, Finland
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8
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Harvey DJ. Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012. MASS SPECTROMETRY REVIEWS 2017; 36:255-422. [PMID: 26270629 DOI: 10.1002/mas.21471] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2014] [Accepted: 01/15/2015] [Indexed: 06/04/2023]
Abstract
This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.
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Affiliation(s)
- David J Harvey
- Department of Biochemistry, Oxford Glycobiology Institute, University of Oxford, Oxford, OX1 3QU, UK
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9
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Prabhu RR, Parashar D, Satyanarayana T. Production and characteristics of the recombinant extracellular bifunctional endoglucanase of the polyextremophilic bacterium Bacillus halodurans and its applicability in saccharifying agro-residues. Bioprocess Biosyst Eng 2016; 40:651-662. [DOI: 10.1007/s00449-016-1730-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Accepted: 12/17/2016] [Indexed: 10/20/2022]
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10
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Characterization of a Cellulomonas fimi exoglucanase/xylanase-endoglucanase gene fusion which improves microbial degradation of cellulosic biomass. Enzyme Microb Technol 2016; 93-94:113-121. [DOI: 10.1016/j.enzmictec.2016.08.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Revised: 08/04/2016] [Accepted: 08/05/2016] [Indexed: 11/17/2022]
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11
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Souza TV, Araujo JN, da Silva VM, Liberato MV, Pimentel AC, Alvarez TM, Squina FM, Garcia W. Chemical stability of a cold-active cellulase with high tolerance toward surfactants and chaotropic agent. ACTA ACUST UNITED AC 2015; 9:1-8. [PMID: 28352586 PMCID: PMC5360981 DOI: 10.1016/j.btre.2015.11.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Revised: 11/19/2015] [Accepted: 11/20/2015] [Indexed: 11/28/2022]
Abstract
CelE1 is a cold-active endo-acting glucanase with high activity at a broad temperature range and under alkaline conditions. Here, we examined the effects of pH on the secondary and tertiary structures, net charge, and activity of CelE1. Although variation in pH showed a small effect in the enzyme structure, the activity was highly influenced at acidic conditions, while reached the optimum activity at pH 8. Furthermore, to estimate whether CelE1 could be used as detergent additives, CelE1 activity was evaluated in the presence of surfactants. Ionic and nonionic surfactants were not able to reduce CelE1 activity significantly. Therefore, CelE1 was found to be promising candidate for use as detergent additives. Finally, we reported a thermodynamic analysis based on the structural stability and the chemical unfolding/refolding process of CelE1. The results indicated that the chemical unfolding proceeds as a reversible two-state process. These data can be useful for biotechnological applications.
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Affiliation(s)
- Thaís V Souza
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, SP, Brazil
| | - Juscemácia N Araujo
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, SP, Brazil
| | - Viviam M da Silva
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, SP, Brazil
| | - Marcelo V Liberato
- Laboratório Nacional de Ciência e Tecnologia do Bioetanol (CTBE), Centro Nacional de Pesquisa em Energia e Materiais (CNPEM), Campinas, SP, Brazil
| | - Agnes C Pimentel
- Laboratório Nacional de Ciência e Tecnologia do Bioetanol (CTBE), Centro Nacional de Pesquisa em Energia e Materiais (CNPEM), Campinas, SP, Brazil
| | - Thabata M Alvarez
- Laboratório Nacional de Ciência e Tecnologia do Bioetanol (CTBE), Centro Nacional de Pesquisa em Energia e Materiais (CNPEM), Campinas, SP, Brazil
| | - Fabio M Squina
- Laboratório Nacional de Ciência e Tecnologia do Bioetanol (CTBE), Centro Nacional de Pesquisa em Energia e Materiais (CNPEM), Campinas, SP, Brazil
| | - Wanius Garcia
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, SP, Brazil
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12
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de Oliveira LC, da Silva VM, Colussi F, Cabral AD, de Oliveira Neto M, Squina FM, Garcia W. Conformational changes in a hyperthermostable glycoside hydrolase: enzymatic activity is a consequence of the loop dynamics and protonation balance. PLoS One 2015; 10:e0118225. [PMID: 25723179 PMCID: PMC4344334 DOI: 10.1371/journal.pone.0118225] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2014] [Accepted: 01/10/2015] [Indexed: 11/20/2022] Open
Abstract
Endo-β-1, 4-mannanase from Thermotoga petrophila (TpMan) is a modular hyperthermostable enzyme involved in the degradation of mannan-containing polysaccharides. The degradation of these polysaccharides represents a key step for several industrial applications. Here, as part of a continuing investigation of TpMan, the region corresponding to the GH5 domain (TpManGH5) was characterized as a function of pH and temperature. The results indicated that the enzymatic activity of the TpManGH5 is pH-dependent, with its optimum activity occurring at pH 6. At pH 8, the studies demonstrated that TpManGH5 is a molecule with a nearly spherical tightly packed core displaying negligible flexibility in solution, and with size and shape very similar to crystal structure. However, TpManGH5 experiences an increase in radius of gyration in acidic conditions suggesting expansion of the molecule. Furthermore, at acidic pH values, TpManGH5 showed a less globular shape, probably due to a loop region slightly more expanded and flexible in solution (residues Y88 to A105). In addition, molecular dynamics simulations indicated that conformational changes caused by pH variation did not change the core of the TpManGH5, which means that only the above mentioned loop region presents high degree of fluctuations. The results also suggested that conformational changes of the loop region may facilitate polysaccharide and enzyme interaction. Finally, at pH 6 the results indicated that TpManGH5 is slightly more flexible at 65°C when compared to the same enzyme at 20°C. The biophysical characterization presented here is well correlated with the enzymatic activity and provide new insight into the structural basis for the temperature and pH-dependent activity of the TpManGH5. Also, the data suggest a loop region that provides a starting point for a rational design of biotechnological desired features.
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Affiliation(s)
- Leandro C de Oliveira
- Departamento de Física, Instituto de Biociências, Letras e Ciências Exatas, UNESP-Univ Estadual Paulista, São José do Rio Preto, SP, Brazil
| | - Viviam M da Silva
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, SP, Brazil
| | - Francieli Colussi
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, SP, Brazil
| | - Aline D Cabral
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, SP, Brazil
| | - Mario de Oliveira Neto
- Departamento de Física e Biofísica, Instituto de Biociências, UNESP-Univ Estadual Paulista, Botucatu, SP, Brazil
| | - Fabio M Squina
- Laboratório Nacional de Ciência e Tecnologia do Bioetanol, Centro Nacional de Pesquisa em Energia e Materiais, Campinas, SP, Brazil
| | - Wanius Garcia
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, SP, Brazil
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13
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Colussi F, da Silva VM, Miller I, Cota J, de Oliveira LC, de Oliveira Neto M, Squina FM, Garcia W. Oligomeric state and structural stability of two hyperthermophilic β-glucosidases from Thermotoga petrophila. Amino Acids 2015; 47:937-48. [PMID: 25637167 DOI: 10.1007/s00726-015-1923-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2014] [Accepted: 01/15/2015] [Indexed: 01/10/2023]
Abstract
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.
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Affiliation(s)
- Francieli Colussi
- Centro de Ciências Naturais e Humanas (CCNH), Universidade Federal do ABC (UFABC), Santo André, SP, Brazil
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14
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Payne CM, Knott BC, Mayes HB, Hansson H, Himmel ME, Sandgren M, Ståhlberg J, Beckham GT. Fungal Cellulases. Chem Rev 2015; 115:1308-448. [DOI: 10.1021/cr500351c] [Citation(s) in RCA: 533] [Impact Index Per Article: 59.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Christina M. Payne
- Department
of Chemical and Materials Engineering and Center for Computational
Sciences, University of Kentucky, 177 F. Paul Anderson Tower, Lexington, Kentucky 40506, United States
| | - Brandon C. Knott
- National
Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver
West Parkway, Golden, Colorado 80401, United States
| | - Heather B. Mayes
- Department
of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
| | - Henrik Hansson
- Department
of Chemistry and Biotechnology, Swedish University of Agricultural Sciences, Uppsala BioCenter, Almas allé 5, SE-75651 Uppsala, Sweden
| | - Michael E. Himmel
- Biosciences
Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Mats Sandgren
- Department
of Chemistry and Biotechnology, Swedish University of Agricultural Sciences, Uppsala BioCenter, Almas allé 5, SE-75651 Uppsala, Sweden
| | - Jerry Ståhlberg
- Department
of Chemistry and Biotechnology, Swedish University of Agricultural Sciences, Uppsala BioCenter, Almas allé 5, SE-75651 Uppsala, Sweden
| | - Gregg T. Beckham
- National
Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver
West Parkway, Golden, Colorado 80401, United States
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15
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Greene ER, Himmel ME, Beckham GT, Tan Z. Glycosylation of Cellulases: Engineering Better Enzymes for Biofuels. Adv Carbohydr Chem Biochem 2015; 72:63-112. [PMID: 26613815 DOI: 10.1016/bs.accb.2015.08.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Cellulose in plant cell walls is the largest reservoir of renewable carbon on Earth. The saccharification of cellulose from plant biomass into soluble sugars can be achieved using fungal and bacterial cellulolytic enzymes, cellulases, and further converted into fuels and chemicals. Most fungal cellulases are both N- and O-glycosylated in their native form, yet the consequences of glycosylation on activity and structure are not fully understood. Studying protein glycosylation is challenging as glycans are extremely heterogeneous, stereochemically complex, and glycosylation is not under direct genetic control. Despite these limitations, many studies have begun to unveil the role of cellulase glycosylation, especially in the industrially relevant cellobiohydrolase from Trichoderma reesei, Cel7A. Glycosylation confers many beneficial properties to cellulases including enhanced activity, thermal and proteolytic stability, and structural stabilization. However, glycosylation must be controlled carefully as such positive effects can be dampened or reversed. Encouragingly, methods for the manipulation of glycan structures have been recently reported that employ genetic tuning of glycan-active enzymes expressed from homogeneous and heterologous fungal hosts. Taken together, these studies have enabled new strategies for the exploitation of protein glycosylation for the production of enhanced cellulases for biofuel production.
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16
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Zhang S, Wang Y, Song X, Hong J, Zhang Y, Yao L. Improving Trichoderma reesei Cel7B Thermostability by Targeting the Weak Spots. J Chem Inf Model 2014; 54:2826-33. [DOI: 10.1021/ci500339v] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Shujun Zhang
- Laboratory
of Biofuels, Qingdao
Institute of Bioenergy and Bioprocess Technology Chinese Academy of Sciences, Qingdao, 266061, China
| | - Yefei Wang
- Laboratory
of Biofuels, Qingdao
Institute of Bioenergy and Bioprocess Technology Chinese Academy of Sciences, Qingdao, 266061, China
| | - Xiangfei Song
- Laboratory
of Biofuels, Qingdao
Institute of Bioenergy and Bioprocess Technology Chinese Academy of Sciences, Qingdao, 266061, China
| | - Jingbo Hong
- Laboratory
of Biofuels, Qingdao
Institute of Bioenergy and Bioprocess Technology Chinese Academy of Sciences, Qingdao, 266061, China
| | - Yu Zhang
- Laboratory
of Biofuels, Qingdao
Institute of Bioenergy and Bioprocess Technology Chinese Academy of Sciences, Qingdao, 266061, China
| | - Lishan Yao
- Laboratory
of Biofuels, Qingdao
Institute of Bioenergy and Bioprocess Technology Chinese Academy of Sciences, Qingdao, 266061, China
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17
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Protein engineering of cellulases. Curr Opin Biotechnol 2014; 29:139-45. [DOI: 10.1016/j.copbio.2014.04.007] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Revised: 04/06/2014] [Accepted: 04/07/2014] [Indexed: 11/21/2022]
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18
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Biochemical characterization of a thermophilic β-mannanase from Talaromyces leycettanus JCM12802 with high specific activity. Appl Microbiol Biotechnol 2014; 99:1217-28. [DOI: 10.1007/s00253-014-5979-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2014] [Revised: 07/21/2014] [Accepted: 07/22/2014] [Indexed: 11/27/2022]
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19
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Carbohydrate-binding modules of fungal cellulases: occurrence in nature, function, and relevance in industrial biomass conversion. ADVANCES IN APPLIED MICROBIOLOGY 2014; 88:103-65. [PMID: 24767427 DOI: 10.1016/b978-0-12-800260-5.00004-8] [Citation(s) in RCA: 83] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In this review, the present knowledge on the occurrence of cellulases, with a special emphasis on the presence of carbohydrate-binding modules (CBMs) in various fungal strains, has been summarized. The importance of efficient fungal cellulases is growing due to their potential uses in biorefinery processes where lignocellulosic biomasses are converted to platform sugars and further to biofuels and chemicals. Most secreted cellulases studied in detail have a bimodular structure containing an active core domain attached to a CBM. CBMs are traditionally been considered as essential parts in cellulases, especially in cellobiohydrolases. However, presently available genome data indicate that many cellulases lack the binding domains in cellulose-degrading organisms. Recent data also demonstrate that CBMs are not necessary for the action of cellulases and they solely increase the concentration of enzymes on the substrate surfaces. On the other hand, in practical industrial processes where high substrate concentrations with low amounts of water are employed, the enzymes have been shown to act equally efficiently with and without CBM. Furthermore, available kinetic data show that enzymes without CBMs can desorb more readily from the often lignaceous substrates, that is, they are not stuck on the substrates and are thus available for new actions. In this review, the available data on the natural habitats of different wood-degrading organisms (with emphasis on the amount of water present during wood degradation) and occurrence of cellulose-binding domains in their genome have been assessed in order to identify evolutionary advantages for the development of CBM-less cellulases in nature.
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20
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Chong BF, Harrison MD, O’Hara IM. Stability of endoglucanases from mesophilic fungus and thermophilic bacterium in acidified polyols. Enzyme Microb Technol 2014; 61-62:55-60. [DOI: 10.1016/j.enzmictec.2014.04.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Revised: 04/23/2014] [Accepted: 04/23/2014] [Indexed: 11/16/2022]
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21
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da Silva VM, Colussi F, de Oliveira Neto M, Braz ASK, Squina FM, Oliveira CLP, Garcia W. Modular hyperthermostable bacterial endo-β-1,4-mannanase: molecular shape, flexibility and temperature-dependent conformational changes. PLoS One 2014; 9:e92996. [PMID: 24671161 PMCID: PMC3966859 DOI: 10.1371/journal.pone.0092996] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Accepted: 02/27/2014] [Indexed: 11/28/2022] Open
Abstract
Endo-β-1,4-mannanase from Thermotoga petrophila (TpMan) is a hyperthermostable enzyme that catalyzes the hydrolysis of β-1,4-mannoside linkages in various mannan-containing polysaccharides. A recent study reported that TpMan is composed of a GH5 catalytic domain joined by a linker to a carbohydrate-binding domain. However, at this moment, there is no three-dimensional structure determined for TpMan. Little is known about the conformation of the TpMan as well as the role of the length and flexibility of the linker on the spatial arrangement of the constitutive domains. In this study, we report the first structural characterization of the entire TpMan by small-angle X-ray scattering combined with the three-dimensional structures of the individual domains in order to shed light on the low-resolution model, overall dimensions, and flexibility of this modular enzyme at different temperatures. The results are consistent with a linker with a compact structure and that occupies a small volume with respect to its large number of amino acids. Furthermore, at 20°C the results are consistent with a model where TpMan is a molecule composed of three distinct domains and that presents some level of molecular flexibility in solution. Even though the full enzyme has some degree of molecular flexibility, there might be a preferable conformation, which could be described by the rigid-body modeling procedure. Finally, the results indicate that TpMan undergoes a temperature-driven transition between conformational states without a significant disruption of its secondary structure. Our results suggest that the linker can optimize the geometry between the other two domains with respect to the substrate at high temperatures. These studies should provide a useful basis for future biophysical studies of entire TpMan.
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Affiliation(s)
- Viviam M. da Silva
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, São Paulo, Brazil
| | - Francieli Colussi
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, São Paulo, Brazil
| | - Mario de Oliveira Neto
- Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, Botucatu, São Paulo, Brazil
| | - Antonio S. K. Braz
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, São Paulo, Brazil
| | - Fabio M. Squina
- Laboratório Nacional de Ciência e Tecnologia do Bioetanol, Centro Nacional de Pesquisa em Energia e Materiais, Campinas, São Paulo, Brazil
| | | | - Wanius Garcia
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), Santo André, São Paulo, Brazil
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22
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Rubin J, Sharma A, Linden L, Bommarius AS, Behrens SH. Gauging Colloidal and Thermal Stability in Human IgG1–Sugar Solutions through Diffusivity Measurements. J Phys Chem B 2014; 118:2803-9. [DOI: 10.1021/jp411185d] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Jonathan Rubin
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0100, United States
- Parker H. Petit Institute of Bioengineering & Biosciences, Georgia Institute of Technology, Atlanta, Georgia 30332-0363, United States
| | - Aditi Sharma
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0100, United States
- Parker H. Petit Institute of Bioengineering & Biosciences, Georgia Institute of Technology, Atlanta, Georgia 30332-0363, United States
| | - Lars Linden
- Bayer
Healthcare AG, Global Biologics, Wuppertal 42096, Germany
| | - Andreas S. Bommarius
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0100, United States
- Parker H. Petit Institute of Bioengineering & Biosciences, Georgia Institute of Technology, Atlanta, Georgia 30332-0363, United States
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States
| | - Sven H. Behrens
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0100, United States
- Parker H. Petit Institute of Bioengineering & Biosciences, Georgia Institute of Technology, Atlanta, Georgia 30332-0363, United States
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23
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Pakarinen A, Haven MØ, Djajadi DT, Várnai A, Puranen T, Viikari L. Cellulases without carbohydrate-binding modules in high consistency ethanol production process. BIOTECHNOLOGY FOR BIOFUELS 2014; 7:27. [PMID: 24559384 PMCID: PMC3974600 DOI: 10.1186/1754-6834-7-27] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Accepted: 02/06/2014] [Indexed: 05/24/2023]
Abstract
BACKGROUND Enzymes still comprise a major part of ethanol production costs from lignocellulose raw materials. Irreversible binding of enzymes to the residual substrate prevents their reuse and no efficient methods for recycling of enzymes have so far been presented. Cellulases without a carbohydrate-binding module (CBM) have been found to act efficiently at high substrate consistencies and to remain non-bound after the hydrolysis. RESULTS High hydrolysis yields could be obtained with thermostable enzymes of Thermoascus aurantiacus containing only two main cellulases: cellobiohydrolase I (CBH I), Cel7A and endoglucanase II (EG II), Cel5A. The yields were decreased by only about 10% when using these cellulases without CBM. A major part of enzymes lacking CBM was non-bound during the most active stage of hydrolysis and in spite of this, produced high sugar yields. Complementation of the two cellulases lacking CBM with CBH II (CtCel6A) improved the hydrolysis. Cellulases without CBM were more sensitive during exposure to high ethanol concentration than the enzymes containing CBM. Enzymes lacking CBM could be efficiently reused leading to a sugar yield of 90% of that with fresh enzymes. The applicability of cellulases without CBM was confirmed under industrial ethanol production conditions at high (25% dry matter (DM)) consistency. CONCLUSIONS The results clearly show that cellulases without CBM can be successfully used in the hydrolysis of lignocellulose at high consistency, and that this approach could provide new means for better recyclability of enzymes. This paper provides new insight into the efficient action of CBM-lacking cellulases. The relationship of binding and action of cellulases without CBM at high DM consistency should, however, be studied in more detail.
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Affiliation(s)
- Annukka Pakarinen
- Department of Food and Environmental Sciences, University of Helsinki, PO 27, 00014 Helsinki, Finland
| | | | - Demi Tristan Djajadi
- Department of Food and Environmental Sciences, University of Helsinki, PO 27, 00014 Helsinki, Finland
| | - Anikó Várnai
- Department of Food and Environmental Sciences, University of Helsinki, PO 27, 00014 Helsinki, Finland
- Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, PO Box 5003, N-1432 Aas, Norway
| | - Terhi Puranen
- Roal Oy, Tykkimäentie 15, FIN-05200 Rajamäki, Finland
| | - Liisa Viikari
- Department of Food and Environmental Sciences, University of Helsinki, PO 27, 00014 Helsinki, Finland
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24
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Engineering chimeric thermostable GH7 cellobiohydrolases in Saccharomyces cerevisiae. Appl Microbiol Biotechnol 2013; 98:2991-3001. [DOI: 10.1007/s00253-013-5177-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Revised: 07/29/2013] [Accepted: 07/30/2013] [Indexed: 10/26/2022]
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25
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26
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Segato F, Damasio ARL, Gonçalves TA, Murakami MT, Squina FM, Polizeli M, Mort AJ, Prade RA. Two structurally discrete GH7-cellobiohydrolases compete for the same cellulosic substrate fiber. BIOTECHNOLOGY FOR BIOFUELS 2012; 5:21. [PMID: 22494694 PMCID: PMC3431977 DOI: 10.1186/1754-6834-5-21] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2011] [Accepted: 03/30/2012] [Indexed: 05/14/2023]
Abstract
BACKGROUND Cellulose consisting of arrays of linear beta-1,4 linked glucans, is the most abundant carbon-containing polymer present in biomass. Recalcitrance of crystalline cellulose towards enzymatic degradation is widely reported and is the result of intra- and inter-molecular hydrogen bonds within and among the linear glucans. Cellobiohydrolases are enzymes that attack crystalline cellulose. Here we report on two forms of glycosyl hydrolase family 7 cellobiohydrolases common to all Aspergillii that attack Avicel, cotton cellulose and other forms of crystalline cellulose. RESULTS Cellobiohydrolases Cbh1 and CelD have similar catalytic domains but only Cbh1 contains a carbohydrate-binding domain (CBD) that binds to cellulose. Structural superpositioning of Cbh1 and CelD on the Talaromyces emersonii Cel7A 3-dimensional structure, identifies the typical tunnel-like catalytic active site while Cbh1 shows an additional loop that partially obstructs the substrate-fitting channel. CelD does not have a CBD and shows a four amino acid residue deletion on the tunnel-obstructing loop providing a continuous opening in the absence of a CBD. Cbh1 and CelD are catalytically functional and while specific activity against Avicel is 7.7 and 0.5 U.mg prot-1, respectively specific activity on pNPC is virtually identical. Cbh1 is slightly more stable to thermal inactivation compared to CelD and is much less sensitive to glucose inhibition suggesting that an open tunnel configuration, or absence of a CBD, alters the way the catalytic domain interacts with the substrate. Cbh1 and CelD enzyme mixtures on crystalline cellulosic substrates show a strong combinatorial effort response for mixtures where Cbh1 is present in 2:1 or 4:1 molar excess. When CelD was overrepresented the combinatorial effort could only be partially overcome. CelD appears to bind and hydrolyze only loose cellulosic chains while Cbh1 is capable of opening new cellulosic substrate molecules away from the cellulosic fiber. CONCLUSION Cellobiohydrolases both with and without a CBD occur in most fungal genomes where both enzymes are secreted, and likely participate in cellulose degradation. The fact that only Cbh1 binds to the substrate and in combination with CelD exhibits strong synergy only when Cbh1 is present in excess, suggests that Cbh1 unties enough chains from cellulose fibers, thus enabling processive access of CelD.
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Affiliation(s)
- Fernando Segato
- Department of Microbiology & Molecular Genetics, Oklahoma State University, Stillwater, OK, USA
- Laboratório Nacional de Ciência e Tecnologia do Bioetanol (CTBE), Centro Nacional de Pesquisas em Energia e Materiais, Campinas, Sao Paulo, Brazil
| | - André R L Damasio
- Department of Microbiology & Molecular Genetics, Oklahoma State University, Stillwater, OK, USA
- Department of Biochemistry, Ribeirão Preto School of Medicine, Ribeirão Preto, Sao Paulo, Brazil
| | - Thiago Augusto Gonçalves
- Laboratório Nacional de Ciência e Tecnologia do Bioetanol (CTBE), Centro Nacional de Pesquisas em Energia e Materiais, Campinas, Sao Paulo, Brazil
| | - Mario T Murakami
- Laboratório Nacional de Biociências (LNBio), Campinas, Sao Paulo, Brazil
| | - Fabio M Squina
- Laboratório Nacional de Ciência e Tecnologia do Bioetanol (CTBE), Centro Nacional de Pesquisas em Energia e Materiais, Campinas, Sao Paulo, Brazil
| | | | - Andrew J Mort
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK, USA
| | - Rolf A Prade
- Department of Microbiology & Molecular Genetics, Oklahoma State University, Stillwater, OK, USA
- Laboratório Nacional de Ciência e Tecnologia do Bioetanol (CTBE), Centro Nacional de Pesquisas em Energia e Materiais, Campinas, Sao Paulo, Brazil
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27
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Chylenski P, Felby C, Østergaard Haven M, Gama M, Selig MJ. Precipitation of Trichoderma reesei commercial cellulase preparations under standard enzymatic hydrolysis conditions for lignocelluloses. Biotechnol Lett 2012; 34:1475-82. [PMID: 22476551 DOI: 10.1007/s10529-012-0916-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Accepted: 03/21/2012] [Indexed: 11/24/2022]
Affiliation(s)
- Piotr Chylenski
- Faculty of Science, University of Copenhagen, Rolighedsvej 23, 1958, Frederiksberg C, Denmark.
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28
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Bansal P, Vowell BJ, Hall M, Realff MJ, Lee JH, Bommarius AS. Elucidation of cellulose accessibility, hydrolysability and reactivity as the major limitations in the enzymatic hydrolysis of cellulose. BIORESOURCE TECHNOLOGY 2012; 107:243-50. [PMID: 22244954 DOI: 10.1016/j.biortech.2011.12.063] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2011] [Revised: 12/11/2011] [Accepted: 12/12/2011] [Indexed: 05/22/2023]
Abstract
The precipitous decline in the rates of enzymatic hydrolysis of cellulose with conversion is one of the major limitations to the commercialization of second-generation biofuel. In this work, various rate-limiting factors (fractal kinetics, changes in crystallinity, accessibility, reactivity and hydrolysable fraction, enzyme clogging, and degree of polymerization) were investigated employing experimental as well as computational studies. Model-guided experiments showed cellulose accessibility and the hydrolysable fraction of accessible substrate (a previously undefined and unreported quantity) to decrease steadily until a conversion level of nearly 70%, while cellulose reactivity, defined in terms of hydrolytic activity per amount of actively adsorbed cellulase, remained constant. Substrate depletion, accessibility and hydrolysability decrease accounted for approximately 90% of rate retardation up to 70% conversion. Faster restart rates were observed on partially converted cellulose as compared to uninterrupted hydrolysis rates, supporting an enzyme clogging phenomenon that could possibly be responsible for the additional rate decrease.
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Affiliation(s)
- Prabuddha Bansal
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, N.W., Atlanta, GA 30332-0100, USA
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