[Show abstract][Hide abstract] ABSTRACT: Select cellulolytic bacteria produce multi-enzymatic cellulosome complexes that bind to the plant cell wall and catalyze its efficient degradation. The multi-modular interconnecting cellulosomal subunits comprise dockerin-containing enzymes that bind cohesively to cohesin-containing scaffoldins. The organization of the modules into functional polypeptides is achieved by intermodular linkers of different lengths and composition, which provide flexibility to the complex and determine its overall architecture.
Using a synthetic biology approach, we systematically investigated the spatial organization of the scaffoldin subunit and its effect on cellulose hydrolysis by designing a combinatorial library of recombinant trivalent designer scaffoldins, which contain a carbohydrate-binding module (CBM) and 3 divergent cohesin modules. The positions of the individual modules were shuffled into 24 different arrangements of chimaeric scaffoldins. This basic set was further extended into three sub-sets for each arrangement with intermodular linkers ranging from zero (no linkers), 5 (short linkers) and native linkers of 27-35 amino acids (long linkers). Of the 72 possible scaffoldins, 56 were successfully cloned and 45 of them expressed, representing 14 full sets of chimaeric scaffoldins. The resultant 42-component scaffoldin library was used to assemble designer cellulosomes, comprising three model C. thermocellum cellulases. Activities were examined using Avicel as a pure microcrystalline cellulose substrate and pretreated cellulose-enriched wheat straw as a model substrate derived from a native source. All scaffoldin combinations yielded active trivalent designer cellulosome assemblies on both substrates that exceeded the levels of the free enzyme systems. A preferred modular arrangement for the trivalent designer scaffoldin was not observed for the three enzymes used in this study, indicating that they could be integrated at any position in the designer cellulosome without significant effect on cellulose-degrading activity. Designer cellulosomes assembled with the long-linker scaffoldins achieved higher levels of activity, compared to those assembled with short-and no-linker scaffoldins.
The results demonstrate the robustness of the cellulosome system. Long intermodular scaffoldin linkers are preferable, thus leading to enhanced degradation of cellulosic substrates, presumably due to the increased flexibility and spatial positioning of the attached enzymes in the complex. These findings provide a general basis for improved designer cellulosome systems as a platform for bioethanol production.
Biotechnology for Biofuels 12/2013; 6(1):182. · 5.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The cellulosome is a large extracellular multi-enzyme complex that facilitates the efficient hydrolysis and degradation of crystalline cellulosic substrates. During the course of our studies on the cellulosome of the rumen bacterium Ruminococcus flavefaciens, we focused on the critical ScaA dockerin (ScaADoc), the unique dockerin that incorporates the primary enzyme-integrating ScaA scaffoldin into the cohesin-bearing ScaB adaptor scaffoldin. In the absence of a high-resolution structure of the ScaADoc module, we generated a computational model, and, upon its analysis, we were surprised to discover a putative stacking interaction between an N-terminal Trp and a C-terminal Pro, which we termed intramolecular clasp. In order to verify the existence of such an interaction, these residues were mutated to alanine. Circular dichroism spectroscopy, intrinsic tryptophan and ANS fluorescence, and NMR spectroscopy indicated that mutation of these residues has a destabilizing effect on the functional integrity of the Ca(2+)-bound form of ScaADoc. Analysis of recently determined dockerin structures from other species revealed the presence of other well-defined intramolecular clasps, which consist of different types of interactions between selected residues at the dockerin termini. We propose that this thematic interaction may represent a major distinctive structural feature of the dockerin module.
[Show abstract][Hide abstract] ABSTRACT: Cellulose-degrading enzyme systems are of significant interest from both a scientific and technological perspective due to the diversity of cellulase families, their unique assembly and substrate binding mechanisms, and their potential applications in several key industrial sectors, notably cellulose hydrolysis for second-generation biofuel production. Particularly fascinating are cellulosomes, the multimodular extracellular complexes produced by numerous anaerobic bacteria. Using single-molecule force spectroscopy, we analyzed the mechanical stability of the intermolecular interfaces between the cohesin and the dockerin modules responsible for self-assembly of the cellulosomal components into the multienzyme complex. The observed cohesin-dockerin rupture forces (>120 pN) are among the highest reported for a receptor-ligand system to date. Using an atomic force microscope protocol that quantified single-molecule binding activity, we observed force-induced dissociation of calcium ions from the duplicated loop-helix F-hand motif located within the dockerin module, which in the presence of EDTA resulted in loss of affinity to the cohesin partner. A cohesin amino acid mutation (D39A) that eliminated hydrogen bonding with the dockerin's critically conserved serine residues reduced the observed rupture forces. Consequently, no calcium loss occurred and dockerin activity was maintained throughout multiple forced dissociation events. These results offer insights at the single-molecule level into the stability and folding of an exquisite class of high-affinity protein-protein interactions that dictate fabrication and architecture of cellulose-degrading molecular machines.
Proceedings of the National Academy of Sciences 11/2012; · 9.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: Microorganisms employ a multiplicity of enzymes to efficiently degrade the composite structure of plant cell wall cellulosic polysaccharides. These remarkable enzyme systems include glycoside hydrolases (cellulases, hemicellulases), polysaccharide lyases, and the carbohydrate esterases. To accomplish this challenging task, several strategies are commonly observed either separately or in combination. These include free enzyme systems, multifunctional enzymes, and multi-enzyme self-assembled designer cellulosome complexes. RESULTS: In order to compare these different paradigms, we employed a synthetic biology approach to convert two different cellulases from the free enzymatic system of the well-studied bacterium, Thermobifida fusca, into bifunctional enzymes with different modular architectures. We then examined their performance compared to those of the combined parental free-enzyme and equivalent designer-cellulosome systems. The results showed that the cellulolytic activity displayed by the different architectures of the bifunctional enzymes was somewhat inferior to that of the wild-type free enzyme system. CONCLUSIONS: The activity exhibited by the designer cellulosome system was equal or superior to that of the free system, presumably reflecting the combined proximity of the enzymes and high flexibility of the designer cellulosome components, thus enabling efficient enzymatic activity of the catalytic modules.
Biotechnology for Biofuels 10/2012; 5(1):78. · 5.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: β-Xylosidases are hemicellulases that hydrolyze short xylo-oligosaccharides into xylose units, thus complementing endoxylanase degradation of the hemicellulose component of lignocellulosic substrates. Here, we describe the cloning, characterization, and kinetic analysis of a glycoside hydrolase family 43 β-xylosidase (Xyl43A) from the aerobic cellulolytic bacterium, Thermobifida fusca. Temperature and pH optima of 55-60 °C and 5.5-6, respectively, were determined. The apparent K(m) value was 0.55 mM, using p-nitrophenyl xylopyranoside as substrate, and the catalytic constant (k(cat)) was 6.72 s(-1). T. fusca Xyl43A contains a catalytic module at the N terminus and an ancillary module (termed herein as Module-A) of undefined function at the C terminus. We expressed the two recombinant modules independently in Escherichia coli and examined their remaining catalytic activity and binding properties. The separation of the two Xyl43A modules caused the complete loss of enzymatic activity, whereas potent binding to xylan was fully maintained in the catalytic module and partially in the ancillary Module-A. Nondenaturing gel electrophoresis revealed a specific noncovalent coupling of the two modules, thereby restoring enzymatic activity to 66.7% (relative to the wild-type enzyme). Module-A contributes a phenylalanine residue that functions as an essential part of the active site, and the two juxtaposed modules function as a single functional entity.
Journal of Biological Chemistry 01/2012; 287(12):9213-21. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: ABSTRACT Lignocellulosic biomass, the most abundant polymer on Earth, is typically composed of three major constituents: cellulose, hemicellulose, and lignin. The crystallinity of cellulose, hydrophobicity of lignin, and encapsulation of cellulose by the lignin-hemicellulose matrix are three major factors that contribute to the observed recalcitrance of lignocellulose. By means of designer cellulosome technology, we can overcome the recalcitrant properties of lignocellulosic substrates and thus increase the level of native enzymatic degradation. In this context, we have integrated six dockerin-bearing cellulases and xylanases from the highly cellulolytic bacterium, Thermobifida fusca, into a chimeric scaffoldin engineered to bear a cellulose-binding module and the appropriate matching cohesin modules. The resultant hexavalent designer cellulosome represents the most elaborate artificial enzyme composite yet constructed, and the fully functional complex achieved enhanced levels (up to 1.6-fold) of degradation of untreated wheat straw compared to those of the wild-type free enzymes. The action of these designer cellulosomes on wheat straw was 33 to 42% as efficient as the natural cellulosomes of Clostridium thermocellum. In contrast, the reduction of substrate complexity by chemical or biological pretreatment of the substrate removed the advantage of the designer cellulosomes, as the free enzymes displayed higher levels of activity, indicating that enzyme proximity between these selected enzymes was less significant on pretreated substrates. Pretreatment of the substrate caused an increase in activity for all the systems, and the native cellulosome completely converted the substrate into soluble saccharides. IMPORTANCE Cellulosic biomass is a potential alternative resource which could satisfy future demands of transportation fuel. However, overcoming the natural lignocellulose recalcitrance remains challenging. Current research and development efforts have concentrated on the efficient cellulose-degrading strategies of cellulosome-producing anaerobic bacteria. Cellulosomes are multienzyme complexes capable of converting the plant cell wall polysaccharides into soluble sugar products en route to biofuels as an alternative to fossil fuels. Using a designer cellulosome approach, we have constructed the largest form of homogeneous artificial cellulosomes reported to date, which bear a total of six different cellulases and xylanases from the highly cellulolytic bacterium Thermobifida fusca. These designer cellulosomes were comparable in size to natural cellulosomes and displayed enhanced synergistic activities compared to their free wild-type enzyme counterparts. Future efforts should be invested to improve these processes to approach or surpass the efficiency of natural cellulosomes for cost-effective production of biofuels.
[Show abstract][Hide abstract] ABSTRACT: During the past several years, major progress has been accomplished in the production of "designer cellulosomes," artificial enzymatic complexes that were demonstrated to efficiently degrade crystalline cellulose. This progress is part of a global attempt to promote biomass waste solutions and biofuel production. In designer cellulosomes, each enzyme is equipped with a dockerin module that interacts specifically with one of the cohesin modules of the chimeric scaffoldin. Artificial scaffoldins serve as docking backbones and contain a cellulose-specific carbohydrate-binding module that directs the enzymatic complex to the cellulosic substrate, and one or more cohesin modules from different natural cellulosomal species, each exhibiting a different specificity, that allows the specific incorporation of the desired matching dockerin-bearing enzymes. With natural cellulosomal components, the insertion of the enzymes in the scaffold would presumably be random, and we would not be able to control the contents of the resulting artificial cellulosome. There are an increasing number of papers describing the production of designer cellulosomes either in vitro, ex vivo, or in vivo. These types of studies are particularly intricate, and a number of such publications are less meaningful in the final analysis, as important controls are frequently excluded. In this chapter, we hope to give a complete overview of the methodologies essential for designing and examining cellulosome complexes.
Methods in enzymology 01/2012; 510:429-52. · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The cellulosome is a large bacterial extracellular multienzyme complex able to degrade crystalline cellulosic substrates. The complex contains catalytic and noncatalytic subunits, interconnected by high-affinity cohesin-dockerin interactions. In this chapter, we introduce an optimized method for comparative binding among different cohesins or cohesin mutants to the dockerin partner. This assay offers advantages over other methods (such as ELISA, cELIA, SPR, and ITC) for particularly high-affinity binding interactions. In this approach, the high-affinity interaction of interest occurs in the liquid phase during the equilibrated binding step, whereas the interaction with the immobilized phase is used only for detection of the unbound dockerins that remain in the solution phase. Once equilibrium conditions are reached, the change in free energy of binding (ΔΔG(binding)), as well as the affinity constant of mutants, can be estimated against the known affinity constant of the wild-type interaction. In light of the above, we propose this method as a preferred alternative for the relative quantification of high-affinity protein interactions.
Methods in enzymology 01/2012; 510:417-28. · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The specificity of cohesin-dockerin interactions is critically important for the assembly of cellulosomal enzymes into the multienzyme cellulolytic complex (cellulosome). In order to investigate the origins of the observed specificity, a variety of selected amino acid positions at the cohesin-dockerin interface can be subjected to mutagenesis, and a library of mutants can be constructed. In this chapter, we describe a protein-protein microarray technique based on the high affinity of a carbohydrate-binding module (CBM), attached to mutant cohesins. Using cellulose-coated glass slides, libraries of mutants can be screened for binding to complementary partners. The advantages of this tool are that crude cell lysate can be used without additional purification, and the microarray can be used for screening both large libraries as initial scanning for "positive" plates, and for small libraries, wherein individual colonies are printed on the slide. Since the time-consuming step of purifying proteins can be circumvented, the approach is also appropriate for providing molecular insight into the multicomponent organization of complex cellulosomes.
Methods in enzymology 01/2012; 510:453-63. · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In nature, the complex composition and structure of the plant cell wall pose a barrier to enzymatic degradation. Nevertheless, some anaerobic bacteria have evolved for this purpose an intriguing, highly efficient multienzyme complex, the cellulosome, which contains numerous cellulases and hemicellulases. The rod-like cellulose component of the plant cell wall is embedded in a colloidal blend of hemicelluloses, a major component of which is xylan. In order to enhance enzymatic degradation of the xylan component of a natural complex substrate (wheat straw) and to study the synergistic action among different xylanases, we have employed a variation of the designer cellulosome approach by fabricating a tetravalent complex that includes the three endoxylanases of Thermobifida fusca (Xyn10A, Xyn10B, and Xyn11A) and an Xyl43A β-xylosidase from the same bacterium. Here, we describe the conversion of Xyn10A and Xyl43A to the cellulosomal mode. The incorporation of the Xyl43A enzyme together with the three endoxylanases into a common designer cellulosome served to enhance the level of reducing sugars produced during wheat straw degradation. The enhanced synergistic action of the four xylanases reflected their immediate juxtaposition in the complex, and these tetravalent xylanolytic designer cellulosomes succeeded in degrading significant (~25%) levels of the total xylan component of the wheat straw substrate. The results suggest that the incorporation of xylanases into cellulosome complexes is advantageous for efficient decomposition of recalcitrant cellulosic substrates--a distinction previously reserved for cellulose-degrading enzymes. IMPORTANCE: Xylanases are important enzymes for our society, due to their variety of industrial applications. Together with cellulases and other glycoside hydrolases, xylanases may also provide cost-effective conversion of plant-derived cellulosic biomass into soluble sugars en route to biofuels as an alternative to fossil fuels. Xylanases are commonly found in multienzyme cellulosome complexes, produced by anaerobic bacteria, which are considered to be among the most efficient systems for degradation of cellulosic biomass. Using a designer cellulosome approach, we have incorporated the entire xylanolytic system of the bacterium Thermobifida fusca into defined artificial cellulosome complexes. The combined action of these designer cellulosomes versus that of the wild-type free xylanase system was then compared. Our data demonstrated that xylanolytic designer cellulosomes displayed enhanced synergistic activities on a natural recalcitrant wheat straw substrate and could thus serve in the development of advanced systems for improved degradation of lignocellulosic material.
[Show abstract][Hide abstract] ABSTRACT: Cellulose, a major component of plant matter, is degraded by a cell surface multiprotein complex called the cellulosome produced by several anaerobic bacteria. This complex coordinates the assembly of different glycoside hydrolases, via a high-affinity Ca(2+)-dependent interaction between the enzyme-borne dockerin and the scaffoldin-borne cohesin modules. In this study, we characterized a new protein affinity tag, ΔDoc, a truncated version (48 residues) of the Clostridium thermocellum Cel48S dockerin. The truncated dockerin tag has a binding affinity (K(A)) of 7.7 × 10(8)M(-1), calculated by a competitive enzyme-linked assay system. In order to examine whether the tag can be used for general application in affinity chromatography, it was fused to a range of target proteins, including Aequorea victoria green fluorescent protein (GFP), C. thermocellum β-glucosidase, Escherichia coli thioesterase/protease I (TEP1), and the antibody-binding ZZ-domain from Staphylococcus aureus protein A. The results of this study significantly extend initial studies performed using the Geobacillus stearothermophilus xylanase T-6 as a model system. In addition, the enzymatic activity of a C. thermocellum β-glucosidase, purified using this approach, was tested and found to be similar to that of a β-glucosidase preparation (without the ΔDoc tag) purified using the standard His-tag. The truncated dockerin derivative functioned as an effective affinity tag through specific interaction with a cognate cohesin, and highly purified target proteins were obtained in a single step directly from crude cell extracts. The relatively inexpensive beaded cellulose-based affinity column was reusable and maintained high capacity after each cycle. This study demonstrates that deletion into the first Ca(2+)-binding loop of the dockerin module results in an efficient and robust affinity tag that can be generally applied for protein purification.
Journal of Molecular Recognition 11/2010; 23(6):525-35. · 3.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cellulosomes are efficient cellulose-degradation systems produced by selected anaerobic bacteria. This multi-enzyme complex is assembled from a group of cellulases attached to a protein scaffold termed scaffoldin, mediated by a high-affinity protein-protein interaction between the enzyme-borne dockerin module and the cohesin module of the scaffoldin. The enzymatic complex is attached as a whole to the cellulosic substrate via a cellulose-binding module (CBM) on the scaffoldin subunit. In previous works, we have employed a synthetic biology approach to convert several of the free cellulases of the aerobic bacterium, Thermobifida fusca, into the cellulosomal mode by replacing each of the enzymes' CBM with a dockerin. Here we show that although family six enzymes are not a part of any known cellulosomal system, the two family six enzymes of the T. fusca system (endoglucanase Cel6A and exoglucanase Cel6B) can be converted to work as cellulosomal enzymes. Indeed, the chimaeric dockerin-containing family six endoglucanase worked well as a cellulosomal enzyme, and proved to be more efficient than the parent enzyme when present in designer cellulosomes. In stark contrast, the chimaeric family six exoglucanase was markedly less efficient than the wild-type enzyme when mixed with other T. fusca cellulases, thus indicating its incompatibility with the cellulosomal mode of action.
Systems and Synthetic Biology 09/2010; 4(3):193-201.
[Show abstract][Hide abstract] ABSTRACT: Conversion of components of the Thermobifida fusca free-enzyme system to the cellulosomal mode using the designer cellulosome approach can be employed to discover the properties and inherent advantages of the cellulosome system. In this article, we describe the conversion of the T. fusca xylanases Xyn11A and Xyn10B and their synergistic interaction in the free state or within designer cellulosome complexes in order to enhance specific degradation of hatched wheat straw as a model for a complex cellulosic substrate. Endoglucanase Cel5A from the same bacterium and its recombinant dockerin-containing chimera were also studied for their combined effect, together with the xylanases, on straw degradation. Synergism was demonstrated when Xyn11A was combined with Xyn10B and/or Cel5A, and approximately 1.5-fold activity enhancements were achieved by the designer cellulosome complexes compared to the free wild-type enzymes. These improvements in activity were due to both substrate-targeting and proximity effects among the enzymes contained in the designer cellulosome complexes. The intrinsic cellulose/xylan-binding module (XBM) of Xyn11A appeared to be essential for efficient substrate degradation. Indeed, only designer cellulosomes in which the XBM was maintained as a component of Xyn11A achieved marked enhancement in activity compared to the combination of wild-type enzymes. Moreover, integration of the XBM in designer cellulosomes via a dockerin module (separate from the Xyn11A catalytic module) failed to enhance activity, suggesting a role in orienting the parent xylanase toward its preferred polysaccharide component of the complex wheat straw substrate. The results provide novel mechanistic insight into the synergistic activity of designer cellulosome components on natural plant cell wall substrates.
Applied and environmental microbiology 06/2010; 76(12):3787-96. · 3.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Protein molecular scaffolds are attracting interest as natural candidates for the presentation of enzymes and acceleration of catalytic reactions. We have previously reported evidence that the stable protein 1 (SP1) from Populustremula can be employed as a molecular scaffold for the presentation of either catalytic or structural binding (cellulosomal cohesin) modules. In the present work, we have displayed a potent exoglucanase (Cel6B) from the aerobic cellulolytic bacterium, Thermobifida fusca, on a cohesin-bearing SP1 scaffold. For this purpose, a chimaeric form of the enzyme, fused to a cellulosomal dockerin module, was prepared. Full incorporation of 12 dockerin-bearing exoglucanase molecules onto the cohesin-bearing scaffold was achieved. Cellulase activity was tested on two cellulosic substrates with different levels of crystallinity, and the activity of the scaffold-linked exoglucanase was significantly reduced, compared to the free dockerin-containing enzyme. However, addition of relatively low concentrations of a free wild-type endoglucanase (T. fusca Cel5A) that bears a cellulose-binding module, in combination with the complexed exoglucanase resulted in a marked rise in activity on both cellulosic substrates. The endoglucanase cleaves internal sites of the cellulose chains, and the new chain ends of the substrate were now readily accessible to the scaffold-borne exoglucanase, thereby resulting in highly effective, synergistic degradation of cellulosic substrates.
Journal of Biotechnology 05/2010; 147(3-4):205-11. · 3.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The anaerobic, thermophilic cellulolytic bacterium Clostridium thermocellum is known for its elaborate cellulosome complex, but it also produces a separate free cellulase system. Among the free enzymes, the noncellulosomal enzyme Cel9I is a processive endoglucanase whose sequence and architecture are very similar to those of the cellulosomal enzyme Cel9R; likewise, the noncellulosomal exoglucanase Cel48Y is analogous to the principal cellulosomal enzyme Cel48S. In this study we used the designer cellulosome approach to examine the interplay of prominent cellulosomal and noncellulosomal cellulases from C. thermocellum. Toward this end, we converted the cellulosomal enzymes to noncellulosomal chimeras by swapping the dockerin module of the cellulosomal enzymes with a carbohydrate-binding module from the free enzyme analogues and vice versa. This enabled us to study the importance of the targeting effect of the free enzymes due to their carbohydrate-binding module and the proximity effect for cellulases on the designer cellulosome. C. thermocellum is the only cellulosome-producing bacterium known to express two different glycoside hydrolase family 48 enzymes and thus the only bacterial system that can currently be used for such studies. The different activities with crystalline cellulose were examined, and the results demonstrated that the individual chimeric cellulases were essentially equivalent to the corresponding wild-type analogues. The wild-type cellulases displayed a synergism of about 1.5-fold; the cellulosomal pair acted synergistically when they were converted into free enzymes, whereas the free enzymes acted synergistically mainly in the wild-type state. The targeting effect was found to be the major factor responsible for the elevated activity observed for these specific enzyme combinations, whereas the proximity effect appeared to play a negligible role.
Applied and environmental microbiology 03/2010; 76(10):3236-43. · 3.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Designer cellulosomes are precision-engineered multienzyme complexes in which the molecular architecture and enzyme content are exquisitely controlled. This system was used to examine enzyme cooperation for improved synergy among Thermobifida fusca glycoside hydrolases. Two T. fusca cellulases, Cel48A exoglucanase and Cel5A endoglucanase, and two T. fusca xylanases, endoxylanases Xyn10B and Xyn11A, were selected as enzymatic components of a mixed cellulase/xylanase-containing designer cellulosome. The resultant mixed multienzyme complex was fabricated on a single scaffoldin subunit bearing all four enzymes. Conversion of T. fusca enzymes to the cellulosomal mode followed by their subsequent incorporation into a tetravalent cellulosome led to assemblies with enhanced activity (~2.4-fold) on wheat straw as a complex cellulosic substrate. The enhanced synergy was caused by the proximity of the enzymes on the complex compared to the free-enzyme systems. The hydrolytic properties of the tetravalent designer cellulosome were compared with the combined action of two separate divalent cellulase- and xylanase-containing cellulosomes. Significantly, the tetravalent designer cellulosome system exhibited an ~2-fold enhancement in enzymatic activity compared to the activity of the mixture of two distinct divalent scaffoldin-borne enzymes. These results provide additional evidence that close proximity between cellulases and xylanases is key to the observed concerted degradation of the complex cellulosic substrate in which the integrated enzymes complement each other by promoting access to the relevant polysaccharide components of the substrate. The data demonstrate that cooperation among xylanases and cellulases can be augmented by their integration into a single designer cellulosome.
[Show abstract][Hide abstract] ABSTRACT: The high-affinity cohesin-dockerin interaction dictates the suprastructural assembly of the multienzyme cellulosome Complex. The interaction between these two complementary families 4 protein modules was found to be species-specific and type-dependent. The structure of the type II cohesin module possesses additional intrinsic secondary structural elements absent in the type I cohesin, i.e., an alpha-helix and two singular "beta-flaps". The role of these extra secondary structures in dockerin recognition was Studied in this work using gene swapping, in which corresponding homologous stretches of types I and II cohesins were interchanged. The specificity of binding of the resultant chimaeric cohesins was determined by enzyme-linked affinity assay. Several chimaeric cohesins retained dockerin recognition properties. Hence, these cohesins may undergo manipulations (insertion/deletion of peptide segments) without altering their affinity toward their counterpart dockerin, although type-dependent binding specificity cannot be converted by swapping of the additional secondary structural elements between the two cohesin types. The results further emphasize the strong affinity and plasticity between the cohesin and dockerin pair and are consistent with the known findings on specificity of the types I and II interactions. These Studies provide insight into the structural and functional resilience of the cohesins and thus have direct bearing on their potential use in biotechnological applications.
Pure and Applied Chemistry. 01/2010; 82(1):193-204.