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1.
微生物纤维素酶的研究现状   总被引:11,自引:0,他引:11  
主要探讨了近年来微生物纤维素酶的研究进展。重点概述了纤维素酶的分子结构、功能、作用机制以及产纤维素酶微生物种类的研究现状,并对该领域的研究问题和前景进行讨论。  相似文献   

2.
纤维素酶的结构及分子多样性   总被引:12,自引:0,他引:12  
概述了纤维素酶的结构、功能、作用机制以及纤维素酶的分子多样性及分子多样性起源的研究进展。  相似文献   

3.
同源建模在纤维素酶分子改造中的应用   总被引:2,自引:0,他引:2  
同源建模技术(homology modeling)给蛋白质的研究带来了新的希望,在理论上解决了结构预测和功能分析以及蛋白质工程实施方面所面临的难题.纤维素酶(cellulase)是能水解纤维素生成纤维二糖和葡萄糖的一组酶的总称.对纤维素酶的研究目前已经发展到结构功能分析、理性设计等方面.由于实验方法不能胜任全部纤维素酶结构的测定工作,故以计算机为依托的同源建模技术便发挥着重要作用,它在纤维素酶分子改造中的应用主要有:家族同源分析、研究功能氨基酸的作用机理、基于分子结构的理性设计、预测突变体结构和新功能等.随着同源建模技术自身的不断完善,以及分子对接、分子动力学模拟等技术的发展,计算机模拟技术将在酶分子的改造过程中显示出巨大的生命力.  相似文献   

4.
细菌纤维素酶的结构和功能及菌种改良研究   总被引:4,自引:2,他引:2  
孙毅  金湘  毛培宏 《生物技术》2005,15(3):87-89
概述了近年来细菌纤维素酶分子结构和功能方面的研究结果,总结了细菌纤维素酶基因的克隆、酶的提取和纯化、纤维分解细菌的改良,展望了该领域的研究前景。  相似文献   

5.
梭热杆菌(Clostridium thermocellum)是一种嗜热厌氧细菌,通过分泌大量纤维素酶高效降解纤维素.根据作用纤维素的不同部位,梭热杆菌分泌的纤维素酶分为内切纤维素酶和外切纤维素酶.纤维小体是由支架蛋白、锚定元件、黏合蛋白、纤维素结合域和催化单位组成的复合体,其独特的结构,使得它可以比真菌纤维素酶更紧密地结合到纤维素表面,这个复合结构结合着多种催化单位,而此特殊的结构是梭热杆菌高效降解纤维素的必要条件.近年来,为更深入透彻地了解纤维小体的结构与功能进行了大量的研究工作,现对相关研究进展进行综述,并给出了未来可能的发展方向.  相似文献   

6.
果蝇Toll和IMD信号通路中的功能结构域   总被引:3,自引:0,他引:3  
功能结构域在蛋白相互关系中起着重要的作用,在细胞信号通路中,上、下游信号分子结构域间的相互作用,传递着信号.赖氨酸型肽聚糖( Lys-typePGN)(来自革兰氏阳性菌)和β-1,3葡聚糖(β-1,3 glucan)(来自真菌)激活果蝇Toll信号通路;二氨基庚二酸型肽聚糖(DAP-type PGN)和脂多糖粗多糖(L...  相似文献   

7.
天然纤维素的结晶区必需在内、外切纤维素酶的协同作用下,始可被降解,这是纤维素降解的限速步骤。内、外切纤维素酶均为β-1,4-糖苷键的水解酶,但单一的内、外切纤维素酶却都不能水解天然纤维素的结晶区。内、外切纤维素酶怎样协同降解纤维素的机理一直未得阐明,是天然纤维素降解机制研究中的难点。纤维素酶分子是由具有催化功能的催化结构域(catalytic domain,CD)和具有结合纤维素功能的纤维素结合(吸附)结构域(cellulse biding domain,CBD)及涟结它们的链结区(linker)序列组成。已知一细菌的CBD在吸附纤维素后,纤维素聚合物断裂形成短小纤维,但这一现象还未在真菌中有类似发现,通过对插入质粒pUC-18上的微紫青霉外切葡聚糖纤维二糖水解酶CBHI的 cDNA基因,进行系列序列定向缺失等体外操作,得到了催化结构域序列缺失的重组质粒,转化大肠杆菌JM109后,利用纤维素结合结构域CBD可吸附纤维素的特性,筛选到含CBD编码区的转化子PUC18G,生产出了LacZ-CBD融合蛋白,经木瓜蛋白酶有限酶切后,分离纯化得到了CBD结构域及其链结区称为:CBDCBHI。经X光衍射、红外光谱分析、热活力测定和扫描电镜观察表明,CBDCBHI吸附纤维素后,能够导致纤维素聚合物氢键断裂,结晶度减低和形成短纤维,从而在底物可及性上为内切葡聚糖酶的水解糖化作用提供了条件,为真菌内、外切纤维素酶协同降解天然纤维素的作用机制提供了实验支持,并提出了内切纤维素酶的水解作用可为外切纤维素酶吸附纤维素提供能量的推论。  相似文献   

8.
Crk是一种重要的细胞内信号接头蛋白,含有SH2和SH3结构域,在信号传递过程中不仅承上启下,对信号强度还有着调控作用.迄今主要发现了4种Crk分子,即v-Crk、CrkⅠ、CrkⅡ和CrkL(Crk-Like).CrkⅡ和CrkL在分子结构上具有高度同源性,但对信号分子却具有不同的偏好性,从而体现出功能差异.本文就接头蛋白Crk的结构、Crk与相互作用蛋白质的作用机制以及与肿瘤的发生发展关系进行了阐述.  相似文献   

9.
I型聚酮合酶(PKSI)的模块型分子结构组织方式非常适合于组合生物合成研究.结构域和模块通过二级组织方式构成了PKSI的催化单元,其它结构多肽则作为“支架”.在“支架”上对结构域和模块两个水平进行突变、替换、插入、缺失等基因操作形成重组PKS,可以理性设计并获得复杂多样的新活性或高活性的聚酮化合物.利用PKSI进行组合生物合成以期获得新聚酮化合物的研究迄今已有约25年,但是目前仍不能够对PKS进行完美的理性设计,快速合成目标活性的新聚酮化合物.PKS中的酰基转移酶结构域的研究在PKS的组合生物合成研究中一直发挥着重要作用.本文结合本课题组的研究基础,对AT结构域的结构、功能及在组合生物合成研究中的最新研究成果作以分析总结.  相似文献   

10.
目的:为了进一步探索抗菌肽分子的作用机制,我们以凡纳对虾具有单个WAP结构域的抗菌肽基因作为研究对象,进行分子生物学方面的分析。方法:通过cDNA全长序列的扩增,以及氨基酸序列的比较分析、系统进化树的分析以及分子结构的初步预测,我们对凡纳对虾SWD分子的结构进行了详细分析。结果:Lv-SWD的cDNA序列全长为434bp,编码92个氨基酸;Lv-SWD存在由24个氨基酸残基形成的信号肽序列,以及由8个保守存在的半胱氨酸残基形成的WAP结构域和一段富含脯氨酸的结构基序。结论:通过这些分子结构的研究,以及与其他SWD分子的比较,作者推测Lv-SWD分子是一种具有抑菌活性的抗菌肽分子,它在凡纳对虾的先天免疫系统中应该发挥着重要的免疫功能。  相似文献   

11.
The order Actinomycetales includes a number of genera that contain species that actively degrade cellulose and these include both mesophilic and facultative thermophilic species. Cellulases produced by strains from two of the genera containing thermophilic organisms have been studied extensively: Microbispora bispora and Thermomonospora fusca. Fractionation of M. bispora cellulases has identified six different enzymes, all of which were purified to near homogeneity and partially characterized. Two of these enzymes appear to be exocellulases and gave synergism with each other and with the endocellulases. The structural genes of five M. bispora cellulases have been cloned and one was sequenced. Fractionation of T. fusca cellulases has identified five different enzymes, all of which were purified to near homogeneity and partially characterized. One of the T. fusca enzymes gives synergism in the hydrolysis of crystalline cellulose with several T. fusca endocellulases and with Trichoderma reesei CBHI but not with T. reesei CBHII. Each T. fusca cellulase contains distinct catalytic and cellulose binding domains. The structural genes of four of the T. fusca endoglucanases have been cloned and sequenced, while three cellulase genes have been cloned from "T. curvata". The T. fusca cellulase genes are expressed at a low level in Escherichia soli, but at a high level in Streptomyces lividans. Sequence comparisons have shown that there are no significant amino acid homologies between any of the catalytic domains of the four T. fusca cellulases, but each of them shows extensive homology to several other cellulases and fits in one of the five existing cellulase gene families. There have been extensive studies of the regulation of the synthesis of these cellulases and a number of regulatory mutants have been isolated. This work has shown that the different T. fusca cellulases are coordinately regulated over a 100-fold range by two independent controls; induction by cellobiose and repression by any good carbon source.  相似文献   

12.
大多数纤维素酶含有催化区和可与纤维素结合且氨基酸序列较为保守的纤维素吸附区(cellulosebindingdomain,CBD)。纤维素吸附区促进酶与底物的结合,有利于催化区对不溶性底物的作用,但对可溶性底物的催化作用无影响。对CBD结构的研究和进一步的诱变研究揭示:纤维素吸附区是通过几个芳香族氨基酸结合到纤维素表面。有实验证明外切葡聚糖酶的CBD对结晶纤维素有疏解作用。CBD结构域已成功地应用于一系列重组融合蛋白的纯化和固定化。对纤维素吸附区结构与功能的深入了解对进一步了解酶的作用机制,促进纤维素酶类生物技术的发展是重要的 。  相似文献   

13.
Abstract

The order Actinomycetales includes a number of genera that contain species that actively degrade cellulose and these include both mesophilic and facultative thermophilic species. Cellulases produced by strains from two of the genera containing thermophilic organisms have been studied extensively: Microbispora bispora and Thermomonospora fusca. Fractionation of M. bispora cellulases has identified six different enzymes, all of which were purified to near homogeneity and partially characterized. Two of these enzymes appear to be exocellulases and gave synergism with each other and with the endocellulases. The structural genes of five M. bispora cellulases have been cloned and one was sequenced. Fractionation of T. fusca cellulases has identified five different enzymes, all of which were purified to near homogeneity and partially characterized. One of the T. fusca enzymes gives synergism in the hydrolysis of crystalline cellulose with several T. fusca endocellulases and with Trichoderma reesei CBHI but not with T. reesei CBHII. Each T. fusca cellulase contains distinct catalytic and cellulose binding domains. The structural genes of four of the T. fusca endoglucanases have been cloned and sequenced, while three cellulase genes have been cloned from “T. curvata”. The T. fusca cellulase genes are expressed at a low level in Escherichia coli, but at a high level in Streptomyces lividans. Sequence comparisons have shown that there are no significant amino acid homologies between any of the catalytic domains of the four T. fusca cellulases, but each of them shows extensive homology to several other cellulases and fits in one of the five existing cellulase gene families. There have been extensive studies of the regulation of the synthesis of these cellulases and a number of regulatory mutants have been isolated. This work has shown that the different T. fusca cellulases are coordinately regulated over a 100-fold range by two independent controls; induction by cellobiose and repression by any good carbon source.  相似文献   

14.
Cellulases hydrolyze β-1,4 glycosidic linkages in cellulose, which are among the most prevalent and stable bonds in Nature. Cellulases comprise many glycoside hydrolase families and exist as processive or nonprocessive enzymes. Product inhibition negatively impacts cellulase action, but experimental measurements of product-binding constants vary significantly, and there is little consensus on the importance of this phenomenon. To provide molecular level insights into cellulase product inhibition, we examine the impact of product binding on processive and nonprocessive cellulases by calculating the binding free energy of cellobiose to the product sites of catalytic domains of processive and nonprocessive enzymes from glycoside hydrolase families 6 and 7. The results suggest that cellobiose binds to processive cellulases much more strongly than nonprocessive cellulases. We also predict that the presence of a cellodextrin bound in the reactant site of the catalytic domain, which is present during enzymatic catalysis, has no effect on product binding in nonprocessive cellulases, whereas it significantly increases product binding to processive cellulases. This difference in product binding correlates with hydrogen bonding between the substrate-side ligand and the cellobiose product in processive cellulase tunnels and the additional stabilization from the longer tunnel-forming loops. The hydrogen bonds between the substrate- and product-side ligands are disrupted by water in nonprocessive cellulase clefts, and the lack of long tunnel-forming loops results in lower affinity of the product ligand. These findings provide new insights into the large discrepancies reported for binding constants for cellulases and suggest that product inhibition will vary significantly based on the amount of productive binding for processive cellulases on cellulose.  相似文献   

15.
    
The structural gene for the major cellulase of Erwinia carotovora subspecies carotovora (Ecc) was isolated and expressed in Escherichia coli. Sequencing of the gene (celV) revealed a typical signal sequence and two functional domains in the enzyme; a catalytic domain linked by a short proline/threonine-rich linker to a cellulose-binding domain (CBD). The deduced amino acid sequence of the catalytic domain showed homology with cellulases of Family A, including enzymes from Bacillus spp. and Erwinia chrysanthemi CelZ, whereas the CBD showed homology with cellulases from several diverse families, supporting a mix-and-match hypothesis for evolution of this domain. Analysis of the substrate specificity of CelV showed it to be an endoglucanase with some exoglucanase activity. The pH optimum is about 7.0 and the temperature optimum about 42°C. CelV is secreted by Ecc and by the taxonomically related Erwinia carotovora subspecies atroseptica (Eca) but not by E. coli. Overproduction of the enzyme from multicopy plasmids in Ecc appears to overload the secretory mechanism.  相似文献   

16.
Murashima K  Kosugi A  Doi RH 《Proteins》2003,50(4):620-628
Clostridium cellulovorans produces a cellulase complex (cellulosome) as well as noncellulosomal cellulases. In this study, we determined a factor that affected the solubility of the cellulosomal cellulase EngB and the noncellulosomal EngD when they were expressed in Escherichia coli. The catalytic domains of EngB and EngD formed inclusion bodies when expressed in E. coli. On the other hand, both catalytic domains containing the C-terminal cellulose-binding domain (CBD) of EngD were expressed in soluble form. Fusion with the CBD of EngD also helped increased the solubility of cellulosomal cellulase EngL upon expression in E. coli. These results indicate that the CBD of EngD plays an important role in the soluble expression of the catalytic domains of EngB, EngL, and EngD. The possible mechanisms of solubilization by fusion of the catalytic domain with the CBD from EngD are discussed.  相似文献   

17.
Cellulases are important glycosyl hydrolases (GHs) that hydrolyze cellulose polymers into smaller oligosaccharides by breaking the cellulose β (1→4) bonds,and they are widely used to produce cellulosic ethanol from the plant biomass.N-linked and O-linked glycosylations were proposed to impact the catalytic efficiency,cellulose binding affinity and the stability of cellulases based on observations of individual cellulases.As far as we know,there has not been any systematic analysis of the distributions of N-...  相似文献   

18.
The structure and mechanism of action of cellulolytic enzymes   总被引:5,自引:0,他引:5  
The modern structural classification of polysaccharases comprising cellulase–hemicellulase enzyme systems is dis cussed. Their catalytic domains are currently grouped into 15 of more than 80 known glycosyl hydrolase families, whereas substrate binding domains fall into 13 families. The structures of catalytic and substrate binding domains, as well as linker sequences, are briefly considered. A hypothetical mechanism of concerted action of catalytic and substrate binding domains of cellobiohydrolases on the surface of highly ordered cellulose is suggested.  相似文献   

19.
20.
Cellulase enzymes deconstruct cellulose to glucose, and are often comprised of glycosylated linkers connecting glycoside hydrolases (GHs) to carbohydrate-binding modules (CBMs). Although linker modifications can alter cellulase activity, the functional role of linkers beyond domain connectivity remains unknown. Here we investigate cellulase linkers connecting GH Family 6 or 7 catalytic domains to Family 1 or 2 CBMs, from both bacterial and eukaryotic cellulases to identify conserved characteristics potentially related to function. Sequence analysis suggests that the linker lengths between structured domains are optimized based on the GH domain and CBM type, such that linker length may be important for activity. Longer linkers are observed in eukaryotic GH Family 6 cellulases compared to GH Family 7 cellulases. Bacterial GH Family 6 cellulases are found with structured domains in either N to C terminal order, and similar linker lengths suggest there is no effect of domain order on length. O-glycosylation is uniformly distributed across linkers, suggesting that glycans are required along entire linker lengths for proteolysis protection and, as suggested by simulation, for extension. Sequence comparisons show that proline content for bacterial linkers is more than double that observed in eukaryotic linkers, but with fewer putative O-glycan sites, suggesting alternative methods for extension. Conversely, near linker termini where linkers connect to structured domains, O-glycosylation sites are observed less frequently, whereas glycines are more prevalent, suggesting the need for flexibility to achieve proper domain orientations. Putative N-glycosylation sites are quite rare in cellulase linkers, while an N-P motif, which strongly disfavors the attachment of N-glycans, is commonly observed. These results suggest that linkers exhibit features that are likely tailored for optimal function, despite possessing low sequence identity. This study suggests that cellulase linkers may exhibit function in enzyme action, and highlights the need for additional studies to elucidate cellulase linker functions.  相似文献   

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