细菌纤维小体的结构和功能

纤维小体(Cellulosome)是多种纤维素酶、半纤维素酶依靠锚定—粘附机制形成的一种多酶复合体结构,通过细胞粘附蛋白附着在细菌细胞壁上,分子量2.0106~2.5106 D,能高效彻底地降解天然纤维素材料。纤维小体的结构和功能是理解原核生物中蛋白与蛋白之间的相互作用和细菌对天然纤维素降解的重要模型。     

生物产纤维素酶研究进展

纤维素酶是降解纤维素最有效的生物催化剂.自然界存在很多产纤维素酶的生物.综述了纤维素酶的类别、族属、结构;产纤维素酶的原生动物、后生动物及微生物菌种(细菌、真菌、放线菌等);目前已发现的编码纤维素酶的基因及其表达;纤维素酶的主要作用机理等方面的研究进展,并就今后的研究方向及重点提出了建议.     

半纤维素酶的分子生物学

对半纤维素酶，主要是木聚糖酶的分子生物学研究进展作了简要评述，包括酶的结构、酶分子的多形性、酶基因克隆与表达等。重点对各种细菌来源和真菌来源的木聚精酶的遗传学研究新进展进行了概括。     

纤维素酶及其分子生物学研究

主要探讨了纤维素酶水解纤维素的作用机理及纤维素酶分子催化区和吸附区的结构和功能。     

细菌纤维素纳米支架材料生物酶解的初步研究

对细菌纤维素的纤维素酶解进行了单因素实验研究,探讨了酶用量、酶解时间及酶解温度等工艺条件对细菌纤维素酶解程度的影响.结果表明:在0.6%～1.6%的酶用量范围内,细菌纤维素的降解程度随酶用量的增加而提高;在0.4%～1.2%的酶用量范围内,细菌纤维素的降解程度随酶解时间的延长而提高,但是在后期增加的程度有所降低;在1～7 d的酶解时间内,细菌纤维素的降解程度随酶解时间的延长而不断提高;在45～55℃的酶解温度范围内,细菌纤维素的降解程度随温度升高呈先升后降的趋势,较适温度为50℃.     

纤维素酶水解及其在能源与环境保护中的应用

纤维素酶的利用是扩大纤维素应用领域和高值化利用纤维素的一条可行的新途径。本文综述了纤维素酶的来源、纤维素酶的结构和组成、纤维素酶解机理及影响因素、纤维素酶在能源及环境保护方面的应用。     

粗纤维素酶液对微晶纤维素酶解的影响因素

栗生灰黑孔菌多被用于产漆酶的研究,很少有利用其纤维素酶的报道。为了降低在纤维素水解中纤维素酶的使用成本,利用栗生灰黑孔菌发酵制备的粗纤维素酶液,以微晶纤维素为底物模型,研究粗纤维素酶液水解微晶纤维素的最佳pH、温度和最佳表面活性剂助剂种类及浓度,并对不同表面活性剂存在条件下的纤维素酶解动力学、紫外和荧光光谱进行了研究。结果表明,粗纤维素酶水解微晶纤维素的最佳条件为pH 4.8,温度50℃,最佳表面活性剂助剂为吐温80,添加剂量为1.12mg/g底物;吐温80的添加可提高粗纤维素酶解的最大反应速度常数V_max,降低米氏常数K_m;表面活性剂改变了纤维素酶的紫外和荧光最大吸收峰,酰胺Ⅰ带和酰胺Ⅲ带的谱峰,可能通过与纤维素酶中的氨基酸残基发生反应影响了纤维素酶的结构,进而影响了微晶纤维素的水解反应。该研究为进一步降低纤维素水解成本提供了理论指导。     

苹果酸脱氢酶协同纤维素酶水解纤维素：理论分析与实验

纤维素分子的刚性结构被认为是限制纤维素酶与底物接触的主要障碍，通过添加纤维素降解辅助蛋白破坏纤维素结构可以有效解决酶对底物的可及性问题。基于文献报道糖苷水解酶家族4 (GH4)成员中α-葡萄糖苷酶对纤维素酶有协同作用，以及α-葡萄糖苷酶与苹果酸脱氢酶(MDH)的蛋白同源性和蛋白结构分析，本文提出MDH也具有协同作用的功能猜想，并开展了MDH协同纤维素酶水解滤纸纤维素的理论以及实验研究。通过分子对接模拟MDH与结晶纤维素的相互作用，理论分析发现MDH可能通过氢键和疏水的作用来降低纤维素的凝聚。实验考察了MDH添加量、纤维素酶量、水解时间等条件对MDH协同纤维素酶水解纤维素的影响。结果表明，在(50±0.50)mg滤纸体系中添加0.06FPU纤维素酶、150μg苹果酸脱氢酶，50℃水浴震荡24h，测定的还原糖产量是纤维素酶单独作用时的(3.47±0.28)倍，MDH对纤维素酶的增效活性为247%±28%。利用扫描电子显微镜(SEM)、X射线衍射(XRD)以及傅里叶变换红外光谱(FTIR)等手段对MDH作用前后的滤纸进行分析，所得结果表明MDH对纤维素的结晶区域具有破坏作用，协同促进了纤维素...     

细菌发酵可望廉价制纤维素乙醇

美国达特茅斯（Dartmoudl）大学的研究人员9月10日发布报告称,采用遗传工程细菌可望较廉价地生产纤维素乙醇。研究表明,自然界中的细菌在较低温度下,可以使纤维素发酵。实验表明,在较高温度下,利用细菌发酵纤维素所需要的时间仅为纤维素酶发酵时间的40％。达特茅斯大学新开发的遗传工程细菌名为ALK2,     

微生物降解纤维素机制的分子生物学研究进展

对纤维素酶的分子生物学，主要是该酶对天然纤维性底物的降解机制研究进展作了简要评述，包括纤维素酶的一、二、三级结构、酶分子的多形性、纤维素酶族、酶基因克隆方法及表达和分泌中存在的问题、新酶分子的构建等。并介绍对细胞融合、单克隆抗体、DNA体外定位诱变、活性中心测定和糖基化方法等在纤维素酶降解研究中的应用。     

Probing the ligand-binding specificity and analyzing the folding state of SPOT-synthesized FBP28 WW domain variants

The WW domains are known as the smallest naturally occurring, monomeric, triple-stranded, antiparallel beta-sheet domains. Hence, we chose the FBP28 WW domain as a model to investigate the stability of the beta-sheet structure at the amino acid level in the context of its function (ligand binding). The structure-function relationship was investigated through a complete substitution analysis of the FBP28 WW domain, with variants synthesized as a cellulose-bound peptide array. The functionality of the FBP28 WW domain variants was examined by probing the peptide array for ligand binding. In addition, selected FBP28 WW domain variants were investigated by CD measurements to determine the stability of the antiparallel beta-sheet structure. We discuss the correlation between structure stability and functionality for the FBP28 WW domain, as well as the effect of ligand-induced structure stabilization.     

An active single-chain antibody containing a cellulase linker domain is secreted by Escherichia coli

Single-chain antibodies consist of the variable, antigen-bindingdomains of antibodies joined to a continuous polypeptide bygenetically engineered peptide linkers. We have used the flexibleinterdomain linker region of a fungal cellulase to link togetherthe variable domains of an anti-2-phenyloxazolone IgGl and showhere that the resulting single-chain antibody is efficientlysecreted and released to the culture medium of Escherichia coli.The yield of affinity-purified single-chain antibody is 1 -2mg/1 of culture medium and its affinity and stability are comparableto those of the corresponding native IgG.     

Two Types of Domain Boundaries in Lanthanum Magnesium Niobate

Microstructural studies of the domain boundaries in the complex perovskite compound lanthanum magnesium niobate (La[Mg_2/3Nb_1/3]O₃, LMN) were conducted using transmission electron microscopy. Both the 1:1 chemical ordering of B-site cations and the tilting of oxygen octahedra affected the domain boundaries. Two types of domain boundaries were observed. In addition to the presence of antiphase boundaries, which were insensitive to the crystallographic planes, ferroelastic domain boundaries that were caused by the phase transition due to the tilting of oxygen octahedra also were present. In some grains, only one type of oxygen tilting was present, which resulted in a single domain in one grain. Two or three domains were observed in a grain where the walls were parallel to the {110} plane. Many domains also were observed in a grain that had boundaries whose linear characteristics were gradually reduced.     

Direct Compositional Analysis of Ordered Domains in Pure and La-Doped Pb(Mg1/3Nb2/3)O3 by Analytical Electron Microscopy Techniques

The ordered domain structures in Pb(Mg_1/3Nb_2/3)O₃(PMN) and Pb_{1– x} La _x (Mg_1/3Nb_2/3)O₃ are identified using high-resolution transmission electron microscopy (HRTEM) and nanobeam diffractometry (NBD). The chemical compositions in the ordered domains and in the disordered matrices are also acquired using energy-dispersive spectroscopy (EDS). The best matching computer-simulated HRTEM image has a Mg²⁺/Nb²⁺ ratio of return ½. There is no obvious chemical composition difference between the ordered domains and the disordered matrices. The number of the normalized total positive valence electrons remains almost constant in the ordered domains and in the disordered matrices for all the samples. The reason for the growth of the ordered domains in La-doped PMN also is discussed.     

Protein structural domain identification

A simple method for the definition of protein structural domainsis described that requires only -carbon coordinate data. Thebasic method, which encodes no specific aspects of protein structure,captures the essence of most domains but does not give highenough priority to the integrity of ß-sheet structure.This aspect was encouraged both by a bias toward attaining intactß-sheets and also as an acceptance condition on the finalresult. The method has only one variable parameter, reflectingthe granularity level of the domains, and an attempt was madeto set this level automatically for each protein based on thebest agreement attained between the domains predicted on thenative structure and a set of smoothed coordinates. While notperfect, this feature allowed some tightly packed domains tobe separated that would have remained undivided had the bestfixed granularity level been used. The quality of the resultswas high and, when compared with a large collection of accepteddomain definitions, only a few could be said to be clearly incorrect.The simplicity of the method allowed its easy extension to thesimultaneous definition of domains across related structuresin a way that does not involve loss of detail through averagingthe structures. This was found to be a useful approach to reconcilingdifferences among structural family members. The method is fast,taking less than 1 s per 100 residues for medium-sized proteins.     

Deleted in Malignant Brain Tumors-1 Protein (DMBT1): A Pattern Recognition Receptor with Multiple Binding Sites

Deleted in Malignant Brain Tumors-1 protein (DMBT1), salivary agglutinin (DMBT1(SAG)), and lung glycoprotein-340 (DMBT1(GP340)) are three names for glycoproteins encoded by the same DMBT1 gene. All these proteins belong to the scavenger receptor cysteine-rich (SRCR) superfamily of proteins: a superfamily of secreted or membrane-bound proteins with SRCR domains that are highly conserved down to sponges, the most ancient metazoa. In addition to SRCR domains, all DMBT1s contain two CUB domains and one zona pellucida domain. The SRCR domains play a role in the function of DMBT1s, which is the binding of a broad range of pathogens including cariogenic streptococci, Helicobacter pylori and HIV. Mucosal defense proteins like IgA, surfactant proteins and lactoferrin also bind to DMBT1s through their SRCR domains. The binding motif on the SRCR domains comprises an 11-mer peptide in which a few amino acids are essential for binding (GRVEVLYRGSW). Adjacent to each individual SRCR domain are glycosylation domains, where the attached carbohydrate chains play a role in the binding of influenza A virus and Helicobacter pylori. The composition of the carbohydrate chains is not only donor specific, but also varies between different organs. These data demonstrate a role for DMBT1s as pattern recognition molecules containing various peptide and carbohydrate binding motifs.     

Short-Range Ordering in Pb(B'1/3B"2/3)O3-Type Relaxor Ferroelectrics

The formation of nonstoichiometric 1:1 ordered nanodomains, which promote B-site microcompositional fluctuation, is known to be one of the most-efficient ways of enhancing diffuse phase transition (DPT) characteristics. A new theory regarding the 1:1 short-range ordering has been developed to account for the observed inability to grow ordered domains beyond the nanometer scale. The dispersion entropy associated with the formation of negatively charged ultrafine domains and the mode of the counter-ion distribution at the domain/matrix interface both have a significant role in controlling the equilibrium ordered domain size.     

Ferroelectric Domain Structure of Lanthanum-Modified Lead Titanate Ceramics

The ferroelectric domain configurations in lanthanummodified lead titanate ceramics have been studied by transmission electron microscopy in conventional, analytical, and high-resolution modes. Results indicate a preponderance of (101), twin-related 90° domains of equilibrium width 50 to 100 nm. These values are consistent with those derived from consideration of elastic strain energy. Below a critical grain size of approximately 0.3 μm, single-domain grains are found. A domain wall energy of 1 mJ/m² was calculated based on this observation. Within such twins are occasionally found ordered domains, displaying little or no misorientation with respect to one another. In addition, (001), 180° domains were observed.     

Identifying Small‐Molecule Binding Sites for Epigenetic Proteins at Domain–Domain Interfaces

Epigenetics is a rapidly growing field in drug discovery. Of particular interest is the role of post‐translational modifications to histones and the proteins that read, write, and erase such modifications. The development of inhibitors for reader domains has focused on single domains. One of the major difficulties of designing inhibitors for reader domains is that, with the notable exception of bromodomains, they tend not to possess a well‐enclosed binding site amenable to small‐molecule inhibition. As many of the proteins in epigenetic regulation have multiple domains, there are opportunities for designing inhibitors that bind at a domain–domain interface which provide a more suitable interaction pocket. Examination of X‐ray structures of multiple domains involved in recognising and modifying post‐translational histone marks using the SiteMap algorithm identified potential binding sites at domain–domain interfaces. For the tandem plant homeodomain–bromodomain of SP100C, a potential inter‐domain site identified computationally was validated experimentally by the discovery of ligands by X‐ray crystallographic fragment screening.