51
|
Telke AA, Zhuang N, Ghatge SS, Lee SH, Ali Shah A, Khan H, Um Y, Shin HD, Chung YR, Lee KH, Kim SW. Engineering of family-5 glycoside hydrolase (Cel5A) from an uncultured bacterium for efficient hydrolysis of cellulosic substrates. PLoS One 2013; 8:e65727. [PMID: 23785445 PMCID: PMC3681849 DOI: 10.1371/journal.pone.0065727] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2013] [Accepted: 04/27/2013] [Indexed: 01/29/2023] Open
Abstract
Cel5A, an endoglucanase, was derived from the metagenomic library of vermicompost. The deduced amino acid sequence of Cel5A shows high sequence homology with family-5 glycoside hydrolases, which contain a single catalytic domain but no distinct cellulose-binding domain. Random mutagenesis and cellulose-binding module (CBM) fusion approaches were successfully applied to obtain properties required for cellulose hydrolysis. After two rounds of error-prone PCR and screening of 3,000 mutants, amino acid substitutions were identified at various positions in thermotolerant mutants. The most heat-tolerant mutant, Cel5A_2R2, showed a 7-fold increase in thermostability. To enhance the affinity and hydrolytic activity of Cel5A on cellulose substrates, the family-6 CBM from Saccharophagus degradans was fused to the C-terminus of the Cel5A_2R2 mutant using overlap PCR. The Cel5A_2R2-CBM6 fusion protein showed 7-fold higher activity than the native Cel5A on Avicel and filter paper. Cellobiose was a major product obtained from the hydrolysis of cellulosic substrates by the fusion enzyme, which was identified by using thin layer chromatography analysis.
Collapse
Affiliation(s)
- Amar A. Telke
- Division of Applied Life Sciences (BK21), PMBBRC, Gyeongsang National University, Jinju, Republic of Korea
| | - Ningning Zhuang
- Division of Applied Life Sciences (BK21), PMBBRC, Gyeongsang National University, Jinju, Republic of Korea
| | - Sunil S. Ghatge
- Division of Applied Life Sciences (BK21), PMBBRC, Gyeongsang National University, Jinju, Republic of Korea
| | - Sook-Hee Lee
- Division of Applied Life Sciences (BK21), PMBBRC, Gyeongsang National University, Jinju, Republic of Korea
| | - Asad Ali Shah
- Division of Applied Life Sciences (BK21), PMBBRC, Gyeongsang National University, Jinju, Republic of Korea
| | - Haji Khan
- Division of Applied Life Sciences (BK21), PMBBRC, Gyeongsang National University, Jinju, Republic of Korea
| | - Youngsoon Um
- Center for Environmental Technology Research, KIST, Seoul, Republic of Korea
| | - Hyun-Dong Shin
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States of America
| | - Young Ryun Chung
- Division of Applied Life Sciences (BK21), PMBBRC, Gyeongsang National University, Jinju, Republic of Korea
| | - Kon Ho Lee
- Division of Applied Life Sciences (BK21), PMBBRC, Gyeongsang National University, Jinju, Republic of Korea
- Department of Microbiology, School of Medicine, Gyeongsang National University, Jinju, Republic of Korea
- * E-mail: (SWK); (KHL)
| | - Seon-Won Kim
- Division of Applied Life Sciences (BK21), PMBBRC, Gyeongsang National University, Jinju, Republic of Korea
- * E-mail: (SWK); (KHL)
| |
Collapse
|
52
|
Insights into exo- and endoglucanase activities of family 6 glycoside hydrolases from Podospora anserina. Appl Environ Microbiol 2013; 79:4220-9. [PMID: 23645193 DOI: 10.1128/aem.00327-13] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The ascomycete Podospora anserina is a coprophilous fungus that grows at late stages on droppings of herbivores. Its genome encodes a large diversity of carbohydrate-active enzymes. Among them, four genes encode glycoside hydrolases from family 6 (GH6), the members of which comprise putative endoglucanases and exoglucanases, some of them exerting important functions for biomass degradation in fungi. Therefore, this family was selected for functional analysis. Three of the enzymes, P. anserina Cel6A (PaCel6A), PaCel6B, and PaCel6C, were functionally expressed in the yeast Pichia pastoris. All three GH6 enzymes hydrolyzed crystalline and amorphous cellulose but were inactive on hydroxyethyl cellulose, mannan, galactomannan, xyloglucan, arabinoxylan, arabinan, xylan, and pectin. PaCel6A had a catalytic efficiency on cellotetraose comparable to that of Trichoderma reesei Cel6A (TrCel6A), but PaCel6B and PaCel6C were clearly less efficient. PaCel6A was the enzyme with the highest stability at 45°C, while PaCel6C was the least stable enzyme, losing more than 50% of its activity after incubation at temperatures above 30°C for 24 h. In contrast to TrCel6A, all three studied P. anserina GH6 cellulases were stable over a wide range of pHs and conserved high activity at pH values of up to 9. Each enzyme displayed a distinct substrate and product profile, highlighting different modes of action, with PaCel6A being the enzyme most similar to TrCel6A. PaCel6B was the only enzyme with higher specific activity on carboxymethylcellulose (CMC) than on Avicel and showed lower processivity than the others. Structural modeling predicts an open catalytic cleft, suggesting that PaCel6B is an endoglucanase.
Collapse
|
53
|
Blifernez-Klassen O, Klassen V, Doebbe A, Kersting K, Grimm P, Wobbe L, Kruse O. Cellulose degradation and assimilation by the unicellular phototrophic eukaryote Chlamydomonas reinhardtii. Nat Commun 2013; 3:1214. [PMID: 23169055 DOI: 10.1038/ncomms2210] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Accepted: 10/15/2012] [Indexed: 12/29/2022] Open
Abstract
Plants convert sunlight to biomass, which is primarily composed of lignocellulose, the most abundant natural biopolymer and a potential feedstock for fuel and chemical production. Cellulose assimilation has so far only been described for heterotrophic organisms that rely on photosynthetically active primary producers of organic compounds. Among phototrophs, the unicellular green microalga Chlamydomonas reinhardtii is widely known as one of the best established model organisms. It occupies many habitats, including aquatic and soil ecosystems. This ubiquity underscores the versatile metabolic properties of this microorganism. Here we present yet another paradigm of adaptation for C. reinhardtii, highlighting its photoheterotrophic ability to utilize cellulose for growth in the absence of other carbon sources. When grown under CO(2)-limiting conditions in the light, secretion of endo-β-1,4-glucanases by the cell causes digestion of exogenous cellulose, followed by cellobiose uptake and assimilation. Phototrophic microbes like C. reinhardtii may thus serve as biocatalysts for cellulosic biofuel production.
Collapse
Affiliation(s)
- Olga Blifernez-Klassen
- Department of Biology, Algae Biotechnology and Bioenergy-Center for Biotechnology (CeBiTec), Bielefeld University, 33615 Bielefeld, Germany
| | | | | | | | | | | | | |
Collapse
|
54
|
Prates ÉT, Stankovic I, Silveira RL, Liberato MV, Henrique-Silva F, Pereira N, Polikarpov I, Skaf MS. X-ray structure and molecular dynamics simulations of endoglucanase 3 from Trichoderma harzianum: structural organization and substrate recognition by endoglucanases that lack cellulose binding module. PLoS One 2013; 8:e59069. [PMID: 23516599 PMCID: PMC3597598 DOI: 10.1371/journal.pone.0059069] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2012] [Accepted: 02/11/2013] [Indexed: 11/18/2022] Open
Abstract
Plant biomass holds a promise for the production of second-generation ethanol via enzymatic hydrolysis, but its utilization as a biofuel resource is currently limited to a large extent by the cost and low efficiency of the cellulolytic enzymes. Considerable efforts have been dedicated to elucidate the mechanisms of the enzymatic process. It is well known that most cellulases possess a catalytic core domain and a carbohydrate binding module (CBM), without which the enzymatic activity can be drastically reduced. However, Cel12A members of the glycosyl hydrolases family 12 (GHF12) do not bear a CBM and yet are able to hydrolyze amorphous cellulose quite efficiently. Here, we use X-ray crystallography and molecular dynamics simulations to unravel the molecular basis underlying the catalytic capability of endoglucanase 3 from Trichoderma harzianum (ThEG3), a member of the GHF12 enzymes that lacks a CBM. A comparative analysis with the Cellulomonas fimi CBM identifies important residues mediating interactions of EG3s with amorphous regions of the cellulose. For instance, three aromatic residues constitute a harboring wall of hydrophobic contacts with the substrate in both ThEG3 and CfCBM structures. Moreover, residues at the entrance of the active site cleft of ThEG3 are identified, which might hydrogen bond to the substrate. We advocate that the ThEG3 residues Asn152 and Glu201 interact with the substrate similarly to the corresponding CfCBM residues Asn81 and Arg75. Altogether, these results show that CBM motifs are incorporated within the ThEG3 catalytic domain and suggest that the enzymatic efficiency is associated with the length and position of the substrate chain, being higher when the substrate interact with the aromatic residues at the entrance of the cleft and the catalytic triad. Our results provide guidelines for rational protein engineering aiming to improve interactions of GHF12 enzymes with cellulosic substrates.
Collapse
Affiliation(s)
- Érica T. Prates
- Institute of Chemistry, State University of Campinas–UNICAMP. Cx.P. 6154, Campinas, São Paulo, Brazil
| | - Ivana Stankovic
- Institute of Chemistry, State University of Campinas–UNICAMP. Cx.P. 6154, Campinas, São Paulo, Brazil
| | - Rodrigo L. Silveira
- Institute of Chemistry, State University of Campinas–UNICAMP. Cx.P. 6154, Campinas, São Paulo, Brazil
| | - Marcelo V. Liberato
- Institute of Physics of São Carlos, University of São Paulo, São Carlos, São Paulo, Brazil
| | - Flávio Henrique-Silva
- Departamento de Genética e Evolução, Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil
| | - Nei Pereira
- Centro de Tecnologia, Escola de Química, Laboratório de Desenvolvimento de Bioprocessos (LaDeBio), Universidade Federal do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, Brazil
| | - Igor Polikarpov
- Institute of Physics of São Carlos, University of São Paulo, São Carlos, São Paulo, Brazil
| | - Munir S. Skaf
- Institute of Chemistry, State University of Campinas–UNICAMP. Cx.P. 6154, Campinas, São Paulo, Brazil
| |
Collapse
|
55
|
Processivity and enzymatic mode of a glycoside hydrolase family 5 endoglucanase from Volvariella volvacea. Appl Environ Microbiol 2012. [PMID: 23204424 DOI: 10.1128/aem.02725-12] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
EG1 is a modular glycoside hydrolase family 5 endoglucanase from Volvariella volvacea consisting of an N-terminal carbohydrate-binding module (CBM1) and a catalytic domain (CD). The ratios of soluble to insoluble reducing sugar produced from filter paper after 8 and 24 h of exposure to EG1 were 6.66 and 8.56, respectively, suggesting that it is a processive endoglucanase. Three derivatives of EG1 containing a core domain only or additional CBMs were constructed in order to evaluate the contribution of the CBM to the processivity and enzymatic mode of EG1 under stationary and agitated conditions. All four enzymatic forms exhibited the same mode of action on both soluble and insoluble cellulosic substrates with cellobiose as a main end product. An additional CBM fused at either the N or C terminus reduced specific activity toward soluble and insoluble celluloses under stationary reaction conditions. Deletion of the CBM significantly decreased enzyme processivity. Insertion of an additional CBM also resulted in a dramatic decrease in processivity in enzyme-substrate reaction mixtures incubated for 0.5 h, but this effect was reversed when reactions were allowed to proceed for longer periods (24 h). Further significant differences were observed in the substrate adsorption/desorption patterns of EG1 and enzyme derivatives equipped with an additional CBM under agitated reaction conditions. An additional family 1 CBM improved EG1 processivity on insoluble cellulose under highly agitated conditions. Our data indicate a strong link between high adsorption levels and low desorption levels in the processivity of EG1 and possibly other processive endoglucanses.
Collapse
|
56
|
Dai X, Zhu Y, Luo Y, Song L, Liu D, Liu L, Chen F, Wang M, Li J, Zeng X, Dong Z, Hu S, Li L, Xu J, Huang L, Dong X. Metagenomic insights into the fibrolytic microbiome in yak rumen. PLoS One 2012; 7:e40430. [PMID: 22808161 PMCID: PMC3396655 DOI: 10.1371/journal.pone.0040430] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2012] [Accepted: 06/06/2012] [Indexed: 11/18/2022] Open
Abstract
The rumen hosts one of the most efficient microbial systems for degrading plant cell walls, yet the predominant cellulolytic proteins and fibrolytic mechanism(s) remain elusive. Here we investigated the cellulolytic microbiome of the yak rumen by using a combination of metagenome-based and bacterial artificial chromosome (BAC)-based functional screening approaches. Totally 223 fibrolytic BAC clones were pyrosequenced and 10,070 ORFs were identified. Among them 150 were annotated as the glycoside hydrolase (GH) genes for fibrolytic proteins, and the majority (69%) of them were clustered or linked with genes encoding related functions. Among the 35 fibrolytic contigs of >10 Kb in length, 25 were derived from Bacteroidetes and four from Firmicutes. Coverage analysis indicated that the fibrolytic genes on most Bacteroidetes-contigs were abundantly represented in the metagenomic sequences, and they were frequently linked with genes encoding SusC/SusD-type outer-membrane proteins. GH5, GH9, and GH10 cellulase/hemicellulase genes were predominant, but no GH48 exocellulase gene was found. Most (85%) of the cellulase and hemicellulase proteins possessed a signal peptide; only a few carried carbohydrate-binding modules, and no cellulosomal domains were detected. These findings suggest that the SucC/SucD-involving mechanism, instead of one based on cellulosomes or the free-enzyme system, serves a major role in lignocellulose degradation in yak rumen. Genes encoding an endoglucanase of a novel GH5 subfamily occurred frequently in the metagenome, and the recombinant proteins encoded by the genes displayed moderate Avicelase in addition to endoglucanase activities, suggesting their important contribution to lignocellulose degradation in the exocellulase-scarce rumen.
Collapse
Affiliation(s)
- Xin Dai
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Yaxin Zhu
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Yingfeng Luo
- CAS Key Laboratory of Genome Sciences and Information, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing, China
| | - Lei Song
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Di Liu
- Bioinformation Center, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Li Liu
- Bioinformation Center, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Furong Chen
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Min Wang
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Jiabao Li
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Xiaowei Zeng
- Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, China
| | - Zhiyang Dong
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Songnian Hu
- CAS Key Laboratory of Genome Sciences and Information, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing, China
| | - Lingyan Li
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Jian Xu
- Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, China
- * E-mail: (X. Dong); (LH); (XD)
| | - Li Huang
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- * E-mail: (X. Dong); (LH); (XD)
| | - Xiuzhu Dong
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- * E-mail: (X. Dong); (LH); (XD)
| |
Collapse
|
57
|
Characterization of a family 5 glycoside hydrolase isolated from the outer membrane of cellulolytic Cytophaga hutchinsonii. Appl Microbiol Biotechnol 2012; 97:3925-37. [DOI: 10.1007/s00253-012-4259-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2012] [Revised: 06/15/2012] [Accepted: 06/19/2012] [Indexed: 11/30/2022]
|
58
|
Cheng G, Datta S, Liu Z, Wang C, Murton JK, Brown PA, Jablin MS, Dubey M, Majewski J, Halbert CE, Browning JF, Esker AR, Watson BJ, Zhang H, Hutcheson SW, Huber DL, Sale KL, Simmons BA, Kent MS. Interactions of endoglucanases with amorphous cellulose films resolved by neutron reflectometry and quartz crystal microbalance with dissipation monitoring. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:8348-58. [PMID: 22554348 DOI: 10.1021/la300955q] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
A study of the interaction of four endoglucanases with amorphous cellulose films by neutron reflectometry (NR) and quartz crystal microbalance with dissipation monitoring (QCM-D) is reported. The endoglucanases include a mesophilic fungal endoglucanase (Cel45A from H. insolens), a processive endoglucanase from a marine bacterium (Cel5H from S. degradans ), and two from thermophilic bacteria (Cel9A from A. acidocaldarius and Cel5A from T. maritima ). The use of amorphous cellulose is motivated by the promise of ionic liquid pretreatment as a second generation technology that disrupts the native crystalline structure of cellulose. The endoglucanases displayed highly diverse behavior. Cel45A and Cel5H, which possess carbohydrate-binding modules (CBMs), penetrated and digested within the bulk of the films to a far greater extent than Cel9A and Cel5A, which lack CBMs. While both Cel45A and Cel5H were active within the bulk of the films, striking differences were observed. With Cel45A, substantial film expansion and interfacial broadening were observed, whereas for Cel5H the film thickness decreased with little interfacial broadening. These results are consistent with Cel45A digesting within the interior of cellulose chains as a classic endoglucanase, and Cel5H digesting predominantly at chain ends consistent with its designation as a processive endoglucanase.
Collapse
Affiliation(s)
- Gang Cheng
- Joint BioEnergy Institute, Emeryville, California, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
59
|
Adav SS, Cheow ESH, Ravindran A, Dutta B, Sze SK. Label free quantitative proteomic analysis of secretome by Thermobifida fusca on different lignocellulosic biomass. J Proteomics 2012; 75:3694-706. [DOI: 10.1016/j.jprot.2012.04.031] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2012] [Revised: 03/25/2012] [Accepted: 04/22/2012] [Indexed: 11/27/2022]
|
60
|
Caldicellulosiruptor core and pangenomes reveal determinants for noncellulosomal thermophilic deconstruction of plant biomass. J Bacteriol 2012; 194:4015-28. [PMID: 22636774 DOI: 10.1128/jb.00266-12] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Extremely thermophilic bacteria of the genus Caldicellulosiruptor utilize carbohydrate components of plant cell walls, including cellulose and hemicellulose, facilitated by a diverse set of glycoside hydrolases (GHs). From a biofuel perspective, this capability is crucial for deconstruction of plant biomass into fermentable sugars. While all species from the genus grow on xylan and acid-pretreated switchgrass, growth on crystalline cellulose is variable. The basis for this variability was examined using microbiological, genomic, and proteomic analyses of eight globally diverse Caldicellulosiruptor species. The open Caldicellulosiruptor pangenome (4,009 open reading frames [ORFs]) encodes 106 GHs, representing 43 GH families, but only 26 GHs from 17 families are included in the core (noncellulosic) genome (1,543 ORFs). Differentiating the strongly cellulolytic Caldicellulosiruptor species from the others is a specific genomic locus that encodes multidomain cellulases from GH families 9 and 48, which are associated with cellulose-binding modules. This locus also encodes a novel adhesin associated with type IV pili, which was identified in the exoproteome bound to crystalline cellulose. Taking into account the core genomes, pangenomes, and individual genomes, the ancestral Caldicellulosiruptor was likely cellulolytic and evolved, in some cases, into species that lost the ability to degrade crystalline cellulose while maintaining the capacity to hydrolyze amorphous cellulose and hemicellulose.
Collapse
|
61
|
Watson BJ, Hammouda B, Briber RM, Hutcheson SW. Influence of organic liquids on the nanostructure of precipitated cellulose. J Appl Polym Sci 2012. [DOI: 10.1002/app.37540] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
62
|
Telke AA, Ghatge SS, Kang SH, Thangapandian S, Lee KW, Shin HD, Um Y, Kim SW. Construction and characterization of chimeric cellulases with enhanced catalytic activity towards insoluble cellulosic substrates. BIORESOURCE TECHNOLOGY 2012; 112:10-7. [PMID: 22409983 DOI: 10.1016/j.biortech.2012.02.066] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2012] [Revised: 02/13/2012] [Accepted: 02/15/2012] [Indexed: 05/11/2023]
Abstract
The chimeric proteins viz. CBM3-Cel9A, CBM4-Cel9A and CBM30-Cel9A, are constructed by fusion of family 3, 4, and 30 cellulose binding modules (CBMs) to N-terminus of family 9 endoglucanase (Cel9A) from Alicyclobacillus acidocaldrious. The chimeric enzymes were successfully expressed in Escherichia coli and purified to homogeneity. The chimeric enzymes showed significant increase in Avicel (8-12 folds) and filter paper (7-10 folds) degradation activities compared to Cel9A endoglucanase. Computational protein modeling and simulation on the chimeric enzymes were applied to analyze the fused CBMs effect on the increased insoluble cellulosic substrates degradation activity. Thin layer chromatography analysis of the enzymatic hydrolysis products and distribution of reducing sugars between soluble and insoluble fractions indicated processive cleavage of insoluble cellulosic substrates by the chimeras. The fused CBMs played a critical accessory role for the Cel9A catalytic domain and changed its character to facilitate the processive cleavage of insoluble cellulosic substrates.
Collapse
Affiliation(s)
- Amar A Telke
- Division of Applied Life Sciences (BK21), PMBBRC, Gyeongsang National University, 900 Gajwa-dong, Jinju, Gyeongnam 660-701, Republic of Korea
| | | | | | | | | | | | | | | |
Collapse
|
63
|
Murphy L, Cruys-Bagger N, Damgaard HD, Baumann MJ, Olsen SN, Borch K, Lassen SF, Sweeney M, Tatsumi H, Westh P. Origin of initial burst in activity for Trichoderma reesei endo-glucanases hydrolyzing insoluble cellulose. J Biol Chem 2012; 287:1252-60. [PMID: 22110134 PMCID: PMC3256860 DOI: 10.1074/jbc.m111.276485] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Revised: 11/10/2011] [Indexed: 11/06/2022] Open
Abstract
The kinetics of cellulose hydrolysis have long been described by an initial fast hydrolysis rate, tapering rapidly off, leading to a process that takes days rather than hours to complete. This behavior has been mainly attributed to the action of cellobiohydrolases and often linked to the processive mechanism of this exo-acting group of enzymes. The initial kinetics of endo-glucanases (EGs) is far less investigated, partly due to a limited availability of quantitative assay technologies. We have used isothermal calorimetry to monitor the early time course of the hydrolysis of insoluble cellulose by the three main EGs from Trichoderma reesei (Tr): TrCel7B (formerly EG I), TrCel5A (EG II), and TrCel12A (EG III). These endo-glucanases show a distinctive initial burst with a maximal rate that is about 5-fold higher than the rate after 5 min of hydrolysis. The burst is particularly conspicuous for TrCel7B, which reaches a maximal turnover of about 20 s(-1) at 30 °C and conducts about 1200 catalytic cycles per enzyme molecule in the initial fast phase. For TrCel5A and TrCel12A the extent of the burst is 2-300 cycles per enzyme molecule. The availability of continuous data on EG activity allows an analysis of the mechanisms underlying the initial kinetics, and it is suggested that the slowdown is linked to transient inactivation of enzyme on the cellulose surface. We propose, therefore, that the frequency of structures on the substrate surface that cause transient inactivation determine the extent of the burst phase.
Collapse
Affiliation(s)
- Leigh Murphy
- From Roskilde University, NSM, Biomaterials, 1 Universitetsvej, DK-4000 Roskilde, Denmark
- Novozymes A/S, Krogshøjvej 36, DK-2880 Denmark
| | - Nicolaj Cruys-Bagger
- From Roskilde University, NSM, Biomaterials, 1 Universitetsvej, DK-4000 Roskilde, Denmark
| | | | | | | | - Kim Borch
- Novozymes A/S, Krogshøjvej 36, DK-2880 Denmark
| | | | | | - Hirosuke Tatsumi
- International Young Researchers Empowerment Center, Shinshu University, Matsumoto, Nagano 390-8621, Japan
| | - Peter Westh
- From Roskilde University, NSM, Biomaterials, 1 Universitetsvej, DK-4000 Roskilde, Denmark
| |
Collapse
|
64
|
Santhanam N, Badri DV, Decker SR, Manter DK, Reardon KF, Vivanco JM. Lignocellulose Decomposition by Microbial Secretions. SIGNALING AND COMMUNICATION IN PLANTS 2012. [DOI: 10.1007/978-3-642-23047-9_7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
|
65
|
Abstract
There are two types of processive cellulases, exocellulases and processive endoglucanases. There are also two classes of exocellulases, ones that attack the reducing ends of cellulose chains and ones that attack the nonreducing ends. There are a number of ways of assaying processivity but none of them are ideal. It appears that exocellulases, all of which have their active sites in a tunnel, couple movement along a cellulose chain with cleavage of cellobiose from the end of the cellulose molecule. There are two sets of structures that suggest how an exocellulase might move along a cellulose chain. For family 48 exocellulases there are two different ways that a chain can be bound in the active site while for family 6 exocellulases there are several different ligand-bound structures. Site-directed mutagenesis of Thermobifida fusca exocellulases Cel48A and Cel6B and the processive endoglucanase Cel9A have identified some mutations that increase processivity and some that decrease processivity. In addition a mutation in Cel6B was identified that appears to allow the mutant enzyme to move along a cellulose chain in the absence of cleavage.
Collapse
Affiliation(s)
- David B Wilson
- Department of Molecular Biology & Genetics, Cornell University, Ithaca, NY, USA.
| | | |
Collapse
|
66
|
Abstract
Natural cellulolytic enzyme systems as well as leading commercial cellulase cocktails are dominated by enzymes that degrade cellulose chains in a processive manner. Despite the abundance of processivity among natural cellulases, the molecular basis as well as the biotechnological implications of this mechanism are only partly understood. One of the major limitations lies in the fact that it is not straightforward to measure and quantify processivity in what essentially are biphasic experimental systems. Here, we describe and discuss both well-established methods and newer methods for measuring cellulase processivity. In addition, we discuss recent insights from studies on chitinases that may help direct further studies on processivity in cellulases.
Collapse
Affiliation(s)
- Svein J Horn
- Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Aas, Norway
| | | | | | | | | |
Collapse
|
67
|
S-layer homology domain proteins Csac_0678 and Csac_2722 are implicated in plant polysaccharide deconstruction by the extremely thermophilic bacterium Caldicellulosiruptor saccharolyticus. Appl Environ Microbiol 2011; 78:768-77. [PMID: 22138994 DOI: 10.1128/aem.07031-11] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The genus Caldicellulosiruptor contains extremely thermophilic bacteria that grow on plant polysaccharides. The genomes of Caldicellulosiruptor species reveal certain surface layer homology (SLH) domain proteins that have distinguishing features, pointing to a role in lignocellulose deconstruction. Two of these proteins in Caldicellulosiruptor saccharolyticus (Csac_0678 and Csac_2722) were examined from this perspective. In addition to three contiguous SLH domains, the Csac_0678 gene encodes a glycoside hydrolase family 5 (GH5) catalytic domain and a family 28 carbohydrate-binding module (CBM); orthologs to Csac_0678 could be identified in all genome-sequenced Caldicellulosiruptor species. Recombinant Csac_0678 was optimally active at 75°C and pH 5.0, exhibiting both endoglucanase and xylanase activities. SLH domain removal did not impact Csac_0678 GH activity, but deletion of the CBM28 domain eliminated binding to crystalline cellulose and rendered the enzyme inactive on this substrate. Csac_2722 is the largest open reading frame (ORF) in the C. saccharolyticus genome (predicted molecular mass of 286,516 kDa) and contains two putative sugar-binding domains, two Big4 domains (bacterial domains with an immunoglobulin [Ig]-like fold), and a cadherin-like (Cd) domain. Recombinant Csac_2722, lacking the SLH and Cd domains, bound to cellulose and had detectable carboxymethylcellulose (CMC) hydrolytic activity. Antibodies directed against Csac_0678 and Csac_2722 confirmed that these proteins bound to the C. saccharolyticus S-layer. Their cellular localization and functional biochemical properties indicate roles for Csac_0678 and Csac_2722 in recruitment and hydrolysis of complex polysaccharides and the deconstruction of lignocellulosic biomass. Furthermore, these results suggest that related SLH domain proteins in other Caldicellulosiruptor genomes may also be important contributors to plant biomass utilization.
Collapse
|
68
|
Processive and nonprocessive cellulases for biofuel production—lessons from bacterial genomes and structural analysis. Appl Microbiol Biotechnol 2011; 93:497-502. [DOI: 10.1007/s00253-011-3701-9] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2011] [Revised: 10/18/2011] [Accepted: 11/01/2011] [Indexed: 01/26/2023]
|
69
|
Complex expression of the cellulolytic transcriptome of Saccharophagus degradans. Appl Environ Microbiol 2011; 77:5591-6. [PMID: 21705539 DOI: 10.1128/aem.00464-11] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Saccharophagus degradans is an aerobic marine bacterium that can degrade cellulose by the induced expression of an unusual cellulolytic system composed of multiple endoglucanases and glucosidases. To understand the regulation of the cellulolytic system, transcript levels for the genes predicted to contribute to the cellulolytic system were monitored by quantitative real-time PCR (qRT-PCR) during the transition to growth on cellulose. Four glucanases of the cellulolytic system exhibited basal expression during growth on glucose. All but one of the predicted cellulolytic system genes were induced strongly during growth on Avicel, with three patterns of expression observed. One group showed increased expression (up to 6-fold) within 4 h of the nutritional shift, with the relative expression remaining constant over the next 22 h. A second group of genes was strongly induced between 4 and 10 h after nutritional transfer, with relative expression declining thereafter. The third group of genes was slowly induced and was expressed maximally after 24 h. Cellodextrins and cellobiose, products of the predicted basally expressed endoglucanases, stimulated expression of representative cellulase genes. A model is proposed by which the activity of basally expressed endoglucanases releases cellodextrins from Avicel that are then perceived and transduced to initiate transcription of each of the regulated cellulolytic system genes forming an expression pattern.
Collapse
|
70
|
Wilson DB. Microbial diversity of cellulose hydrolysis. Curr Opin Microbiol 2011; 14:259-63. [PMID: 21531609 DOI: 10.1016/j.mib.2011.04.004] [Citation(s) in RCA: 175] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Revised: 03/31/2011] [Accepted: 04/06/2011] [Indexed: 01/10/2023]
Abstract
Enzymatic hydrolysis of cellulose by microorganisms is a key step in the global carbon cycle. Despite its abundance only a small percentage of microorganisms can degrade cellulose, probably because it is present in recalcitrant cell walls. There are at least five distinct mechanisms used by different microorganisms to degrade cellulose all of which involve cellulases. Cellulolytic organisms and cellulases are extremely diverse possibly because their natural substrates, plant cell walls, are very diverse. At this time the microbial ecology of cellulose degradation in any environment is still not clearly understood even though there is a great deal of information available about the bovine rumen. Two major problems that limit our understanding of this area are the vast diversity of organisms present in most cellulose degrading environments and the inability to culture most of them.
Collapse
Affiliation(s)
- David B Wilson
- Department of Molecular Biology & Genetics, 458 Biotechnology Building, Cornell University, Ithaca, NY 14853, United States.
| |
Collapse
|
71
|
Hutcheson SW, Zhang H, Suvorov M. Carbohydrase systems of Saccharophagus degradans degrading marine complex polysaccharides. Mar Drugs 2011; 9:645-665. [PMID: 21731555 PMCID: PMC3124978 DOI: 10.3390/md9040645] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Revised: 04/01/2011] [Accepted: 04/13/2011] [Indexed: 11/16/2022] Open
Abstract
Saccharophagus degradans 2-40 is a γ-subgroup proteobacterium capable of using many of the complex polysaccharides found in the marine environment for growth. To utilize these complex polysaccharides, this bacterium produces a plethora of carbohydrases dedicated to the processing of a carbohydrate class. Aiding in the identification of the contributing genes and enzymes is the known genome sequence for this bacterium. This review catalogs the genes and enzymes of the S. degradans genome that are likely to function in the systems for the utilization of agar, alginate, α- and β-glucans, chitin, mannans, pectins, and xylans and discusses the cell biology and genetics of each system as it functions to transfer carbon back to the bacterium.
Collapse
Affiliation(s)
- Steven W. Hutcheson
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA
| | - Haitao Zhang
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA
- Zymetis, Inc., 387 Technology Drive, College Park, MD 20742, USA; E-Mails: (H.Z.); (M.S.)
| | - Maxim Suvorov
- Zymetis, Inc., 387 Technology Drive, College Park, MD 20742, USA; E-Mails: (H.Z.); (M.S.)
| |
Collapse
|
72
|
Zhang H, Moon YH, Watson BJ, Suvorov M, Santos E, Sinnott CA, Hutcheson SW. Hydrolytic and phosphorolytic metabolism of cellobiose by the marine aerobic bacterium Saccharophagus degradans 2-40T. J Ind Microbiol Biotechnol 2011; 38:1117-25. [PMID: 21327449 DOI: 10.1007/s10295-011-0945-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2010] [Accepted: 01/21/2011] [Indexed: 11/27/2022]
Abstract
Saccharophagus degradans 2-40 is a marine gamma proteobacterium that can produce polyhydroxyalkanoates from lignocellulosic biomass using a complex cellulolytic system. This bacterium has been annotated to express three surface-associated β-glucosidases (Bgl3C, Ced3A, and Ced3B), two cytoplasmic β-glucosidases (Bgl1A and Bgl1B), and unusual for an aerobic bacterium, two cytoplasmic cellobiose/cellodextrin phosphorylases (Cep94A and Cep94B). Expression of the genes for each of the above enzymes was induced when cells were transferred into a medium containing Avicel as the major carbon source except for Bgl1B. Both hydrolytic and phosphorolytic degradation of cellobiose by crude cell lysates obtained from cellulose-grown cells were demonstrated and all of these activities were cell-associated. With the exception of Cep94B, each purified enzyme exhibited their annotated activity upon cloning and expression in E. coli. The five β-glucosidases hydrolyzed a variety of glucose derivatives containing β-1, (2, 4, or 6) linkages but did not act on any α-linked glucose derivatives. All but one β-glucosidases exhibited transglycosylation activity consistent with the formation of an enzyme-substrate intermediate. The biochemistry and expression of these cellobiases indicate that external hydrolysis by surface-associated β-glucosidases coupled with internal hydrolysis and phosphorolysis are all involved in the metabolism of cellobiose by this bacterium.
Collapse
Affiliation(s)
- Haitao Zhang
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA
| | | | | | | | | | | | | |
Collapse
|
73
|
Synergy, Structure and Conformational Flexibility of Hybrid Cellulosomes Displaying Various Inter-cohesins Linkers. J Mol Biol 2011; 405:143-57. [DOI: 10.1016/j.jmb.2010.10.013] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2010] [Revised: 10/07/2010] [Accepted: 10/12/2010] [Indexed: 11/17/2022]
|
74
|
Kurasin M, Väljamäe P. Processivity of cellobiohydrolases is limited by the substrate. J Biol Chem 2010; 286:169-77. [PMID: 21051539 DOI: 10.1074/jbc.m110.161059] [Citation(s) in RCA: 184] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Processive cellobiohydrolases (CBHs) are the key components of fungal cellulase systems. Despite the wealth of structural data confirming the processive mode of action, little quantitative information on the processivity of CBHs is available. Here, we developed a method for measuring cellulase processivity. Sensitive fluorescence detection of enzyme-generated insoluble reducing groups on cellulose after labeling with diaminopyridine enabled quantification of the number of reducing-end exo-mode and endo-mode initiations. Both CBHs TrCel7A from Trichoderma reesei and PcCel7D from Phanerochaete chrysosporium employed reducing-end exo- and endo-mode initiation in parallel. Processivity values measured for TrCel7A and PcCel7D on cellulose hydrolysis were more than an order of magnitude lower than the values of intrinsic processivity that were found from the ratio of catalytic constant (k(cat)) and dissociation rate constant (k(off)). We propose that the length of the obstacle-free path available for a processive run on cellulose chain limits the processivity of CBHs on cellulose. TrCel7A and PcCel7D differed in their k(off) values, whereas the k(cat) values were similar. Furthermore, the k(off) values for endoglucanases (EGs) were much higher than the k(off) values for CBHs, whereas the k(cat) values for EGs and CBHs were within the same order of magnitude. These results suggest that the value of k(off) may be the primary target for the selection of cellulases.
Collapse
Affiliation(s)
- Mihhail Kurasin
- Institute of Molecular and Cell Biology, University of Tartu, Tartu 51014, Estonia
| | | |
Collapse
|
75
|
A novel salt-tolerant endo-beta-1,4-glucanase Cel5A in Vibrio sp. G21 isolated from mangrove soil. Appl Microbiol Biotechnol 2010; 87:1373-82. [PMID: 20393708 DOI: 10.1007/s00253-010-2554-y] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2009] [Revised: 03/09/2010] [Accepted: 03/11/2010] [Indexed: 10/19/2022]
Abstract
Although cellulases have been isolated from various microorganisms, no functional cellulase gene has been reported in the Vibrio genus until now. In this report, a novel endo-beta-1,4-glucanase gene, cel5A, 1,362 bp in length, was cloned from a newly isolated bacterium, Vibrio sp. G21. The deduced protein of cel5A contains a catalytic domain of glycosyl hydrolase family 5 (GH5), followed by a cellulose binding domain (CBM2). The GH5 domain shows the highest sequence similarity (69%) to the bifunctional beta 1,4-endoglucanase/cellobiohydrolase from Teredinibacter turnerae T7902. The mature Cel5A enzyme was overexpressed in Escherichia coli and purified to homogeneity. The optimal pH and temperature of the recombinant enzyme were determined to be 6.5-7.5 and 50 degrees C, respectively. Cel5A was stable over a wide range of pH and retained more than 90% of total activity even after treatment in pH5.5-10.5 for 1 h, indicating high alkali resistance. Moreover, the enzyme was activated after pretreatment with mild alkali, a novel characteristic that has not been previously reported in other cellulases. Cel5A also showed a high level of salt tolerance. Its activity rose to 1.6-fold in 0.5 M NaCl and remained elevated even in 4 M NaCl. Further experimentation demonstrated that the thermostability of Cel5A was improved in 0.4 M NaCl. In addition, Cel5A showed specific activity towards beta-1,4-linkage of amorphous region of lignocellulose, and the main final hydrolysis product of carboxymethylcellulose sodium and cellooligosaccharides was cellobiose. As an alkali-activated and salt-tolerant enzyme, Cel5A is an ideal candidate for further research and industrial applications.
Collapse
|
76
|
Requirement of the type II secretion system for utilization of cellulosic substrates by Cellvibrio japonicus. Appl Environ Microbiol 2010; 76:5079-87. [PMID: 20543053 DOI: 10.1128/aem.00454-10] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cellulosic biofuels represent a powerful alternative to petroleum but are currently limited by the inefficiencies of the conversion process. While gram-positive and fungal organisms have been widely explored as sources of cellulases and hemicellulases for biomass degradation, gram-negative organisms have received less experimental attention. We investigated the ability of Cellvibrio japonicus, a recently sequenced gram-negative cellulolytic bacterium, to degrade bioenergy-related feedstocks. Using a newly developed biomass medium, we showed that C. japonicus is able to utilize corn stover and switchgrass as sole sources of carbon and energy for growth. We also developed tools for directed gene disruptions in C. japonicus and used this system to construct a mutant in the gspD gene, which is predicted to encode a component of the type II secretion system. The gspD::pJGG1 mutant displayed a greater-than-2-fold decrease in endoglucanase secretion compared to wild-type C. japonicus. In addition, the mutant strain showed a pronounced growth defect in medium with biomass as a carbon source, yielding 100-fold fewer viable cells than the wild type. To test the potential of C. japonicus to undergo metabolic engineering, we constructed a strain able to produce small amounts of ethanol from biomass. Collectively, these data suggest that C. japonicus is a useful platform for biomass conversion and biofuel production.
Collapse
|
77
|
Engineering a family 9 processive endoglucanase from Paenibacillus barcinonensis displaying a novel architecture. Appl Microbiol Biotechnol 2009; 86:1125-34. [DOI: 10.1007/s00253-009-2350-8] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Revised: 11/04/2009] [Accepted: 11/09/2009] [Indexed: 11/26/2022]
|
78
|
The noncellulosomal family 48 cellobiohydrolase from Clostridium phytofermentans ISDg: heterologous expression, characterization, and processivity. Appl Microbiol Biotechnol 2009; 86:525-33. [PMID: 19830421 DOI: 10.1007/s00253-009-2231-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Revised: 08/29/2009] [Accepted: 08/31/2009] [Indexed: 10/20/2022]
Abstract
Family 48 glycoside hydrolases (cellobiohydrolases) are among the most important cellulase components for crystalline cellulose hydrolysis mediated by cellulolytic bacteria. Open reading frame (Cphy_3368) of Clostridium phytofermentans ISDg encodes a putative family 48 glycoside hydrolase (CpCel48) with a family 3 cellulose-binding module. CpCel48 was successfully expressed as two soluble intracellular forms with or without a C-terminal His-tag in Escherichia coli and as a secretory active form in Bacillus subtilis. It was found that calcium ion enhanced activity and thermostability of the enzyme. CpCel48 had high activities of 15.1 U micromol(-1) on Avicel and 35.9 U micromol(-1) on regenerated amorphous cellulose (RAC) with cellobiose as a main product and cellotriose and cellotetraose as by-products. By contrast, it had very weak activities on soluble cellulose derivatives (e.g., carboxymethyl cellulose (CMC)) and did not significantly decrease the viscosity of the CMC solution. Cellotetraose was the smallest oligosaccharide substrate for CpCel48. Since processivity is a key characteristic for cellobiohydrolases, the new initial false/right attack model was developed for estimation of processivity by considering the enzyme's substrate specificity, the crystalline structure of homologous Cel48 enzymes, and the configuration of cellulose chains. The processivities of CpCel48 on Avicel and RAC were estimated to be approximately 3.5 and 6.0, respectively. Heterologous expression of secretory active cellobiohydrolase in B. subtilis is an important step for developing recombinant cellulolytic B. subtilis strains for low-cost production of advanced biofuels from cellulosic materials in a single step.
Collapse
|