Thermostable β-Glycosidase from Sulfolobus Solfataricus

The Sulfolobus solfataricus β-glycosidase (Sβgly) is a thermostable and thermophilic glycosyl-hydrolase with broad substrate specificity. The enzyme hydrolizes β-D-gluco-, fuco-, and galactosides, and a large number of /Winked glycoside dimers and oligomers, linked β1-3, β1-4, and β1-6, It is able to hydrolize oligosaccharides with up to 5 glucose residues. Furthermore, it is also able to promote transglycosylation reactions. The corresponding gene has been cloned and overexpressed both in yeast and Escherichia coli. Based on sequence and functional data, the Sβgly has been assigned to the so-called BGA family of glycosyl-hydrolases, including β-glycosidases, β-galactosidases and phosho-β-galactosidases from mesophilic and thermophilic organisms of the three domains. The Sβgly has been crystallized and the resolution of its structure is in progress. Because of its special properties, the enzymes has considerable biotechnological potential.     

Emulsion liquid membrane extraction of lactic acid from aqueous solutions and fermentation broth

Studies on the batch extraction of lactic acid using an emulsion liquid membrane system are reported. The membrane phase consists of the tertiary amine carrier Alamine 336 and the surfactant Span 80 dissolved in n-heptane/paraffin and aqueous solutions of sodium carbonate in the internal phase. The effects of internal phase reagent, extraction temperature, and initial external phase pH on the extraction efficiency and the emulsion swelling are examined. A statistical factorial experiment on extraction from clarified lactic acid fermentation broth was carried out to obtain knowledge of the performance of the extraction system from a broth. The extraction efficiency from the fermentation broth is found to be lower as compared to aqueous solutions of pure lactic acid. The effect of pH and the presence of other ionic species on selectivity are discussed. (c) 1993 John Wiley & Sons, Inc.     

Extractive separation of penicillin G by facilitated transport via carrier supported liquid membranes

The facilitated transport of penicillin G (Pen G), through a supported liquid membrane with Amberlite LA-2 dissolved in 1-decanol, supported on a microporous polypropylene membrane, were studied. The distribution coefficient was obtained from a batch extraction experiment. The effects of flow rate, carrier concentration, initial concentration of Pen G, and the pH of feed and stripping phases on the transport rate of Pen G through the supported liquid membrane were also investigated. The results are in agreement with theoretical predictions, and it is demonstrated that the transport of Pen G through the supported liquid membrane is controlled simultaneously by mass transfer across both aqueous and liquid membranes. (c) 1993 John Wiley & Sons, Inc.     

Cyclic dipeptide-based small molecules modulate zinc-mediated liquid–liquid phase separation of tau

Liquid–liquid phase separation (LLPS) is a complex physicochemical phenomenon mediated by multivalent transient weak interactions among macromolecules like polymers, proteins, and nucleic acids. It has implications in cellular physiology and disease conditions like cancer and neurodegenerative disorders. Many proteins associated with neurodegenerative disorders like RNA binding protein FUS (FUsed in Sarcoma), alpha-synuclein (α-Syn), TAR DNA binding protein 43 (TDP-43), and tau are shown to undergo LLPS. Recently, the tau protein responsible for Alzheimer's disease (AD) and other tauopathies is shown to phase separate into condensates in vitro and in vivo. The diverse noncovalent interactions among the biomolecules dictate the complex LLPS phenomenon. There are limited chemical tools to modulate protein LLPS which has therapeutic potential for neurodegenerative disorders. We have rationally designed cyclic dipeptide (CDP)-based small-molecule modulators (SMMs) by integrating multiple chemical groups that offer diverse chemical interactions to modulate tau LLPS. Among them, compound 1c effectively inhibits and dissolves Zn-mediated tau LLPS condensates. The SMM also inhibits tau condensate-to-fibril transition (tau aggregation through LLPS). This approach of designing SMMs of LLPS establishes a novel platform that has potential implication for the development of therapeutics for neurodegenerative disorders.     

Identification of Products from Oxidation of Uric Acid Induced by Hydroxyl Radicals

The aim of the present study was to separate and characterise products formed by oxidation of uric acid by hydroxyl radicals with a view to probing for these products in vivo in clinical contexts. Aerated solutions of 200 μM uric acid, or its oxidation products, allantoin or parabanic acid, were exposed to gamma radiolysis, (52.0 Gy/min), as a source of HO- radicals, at pH 3.4 and 7.4. Aliquots were taken every 5 minutes for 20 minutes and oxidation products were separated by HPLC and analysed with a diode array detector. Identities of oxidation products were confirmed on the basis of similarity of retention times and absorbance spectra and peak purity parameters of known standards. Hydroperoxides were measured by tri-iodide formation in the 20 minute sample. Exposure of uric acid to such HO fluxes produced a net loss of the parent compound with formation of a complex mixture of products with allantoin and parabanic acid being the predominant products at pH 3.4. The rate of uric acid degradation at physiological pH was slower and the distribution of oxidation products was different. A small but significant amount of uric acid hydroperoxide was detected at both pHs. A mechanism for uric acid oxidation under these conditions is presented.     

Crevice-forming mutants in the rigid core of bovine pancreatic trypsin inhibitor: crystal structures of F22A, Y23A, N43G, and F45A.

Crystal structures of four mutants of bovine pancreatic trypsin inhibitor (F22A, Y23A, N43G, and F45A), engineered to alter their stability properties, have been determined. The mutated residues, which are highly conserved among Kunitz-type inhibitors, are located in the rigid core of the molecule. Replacement of the partially buried bulky residues of the wild-type protein with smaller residues resulted in crevices open to the exterior of the molecule. The overall three-dimensional structure of these mutants is very similar to that of the wild-type protein and only small rearrangements are observed among the atoms lining the crevices.     

Macromolecular solvation energies derived from small molecule crystal morphology.

The morphology of small molecule crystals provides a model for evaluating surface solvation energies in a system with similar packing density to that observed for amino acid residues in proteins. The solvation energies associated with the transfer of methylene and carboxyl groups between vacuum and aqueous phases are estimated to be approx. $40 and -260 cal/A2, respectively, from an analysis of the morphology of succinic acid crystals. These solvation energies predict values for contact angles in reasonable agreement with measurements determined from macroscopic monolayer surfaces. Transfer free energies between vapor and water phases for a series of carboxylic acids are also predicted reasonably well by these solvation energies, provided the surface exposure of different groups is quantitated with the molecular surface area rather than the more traditional accessible surface area. In general, molecular surfaces and molecular surface areas are seen to have important advantages for characterizing the structure and energetics of macromolecular surfaces. Crystal faces of succinic acid with the lowest surface energies in aqueous solution are characteristically smooth. Increasing surface roughness and apolarity are associated with higher surface energies, which suggests an approach for modifying the surface properties of proteins and other macromolecules.     

Crystal structure of human annexin I at 2.5 A resolution.

cDNA coding for N-terminally truncated human annexin I, a member of the family of Ca(2+)-dependent phospholipid binding proteins, has been cloned and expressed in Escherichia coli. The expressed protein is biologically active, and has been purified and crystallized in space group P2(1)2(1)2(1) with cell dimensions a = 139.36 A, b = 67.50 A, and c = 42.11 A. The crystal structure has been determined by molecular replacement at 3.0 A resolution using the annexin V core structure as the search model. The average backbone deviation between these two structures is 2.34 A. The structure has been refined to an R-factor of 17.7% at 2.5 A resolution. Six calcium sites have been identified in the annexin I structure. Each is located in the loop region of the helix-loop-helix motif. Two of the six calcium sites in annexin I are not occupied in the annexin V structure. The superpositions of the corresponding loop regions in the four domains show that the calcium binding loops in annexin I can be divided into two classes: type II and type III. Both classes are different from the well-known EF-hand motif (type I).     

聚苯乙烯纳米塑料-植物蛋白冠的形成与特征

为探究聚苯乙烯纳米塑料-植物蛋白冠的形成过程以及蛋白冠的形成对植物可能造成的影响,本研究选用3种平均粒径为200nm不同表面修饰的聚苯乙烯纳米塑料微球和新几内亚凤仙(Impatiens hawkeri)为对象,将3种聚苯乙烯纳米塑料分别与新几内亚凤仙的叶蛋白提取物进行反应,反应时间分别为2、4、8、16、24、36 h。利用扫描电镜(scanning electron microscopy, SEM)观察其形貌变化,原子力显微镜(atomic force microscopy, AFM)进行表面粗糙度测定,使用纳米粒度和zeta电位分析仪测定水合粒径及zeta电位,液相色谱-串联质谱(liquid chromatography-tandem mass spectrometry, LC-MS/MS)鉴定蛋白冠的蛋白成分。从生物学过程、细胞组分以及分子功能3个方面对蛋白进行分类,研究不同表面修饰的纳米塑料对蛋白的吸附选择,探究聚苯乙烯纳米塑料-植物蛋白冠的形成与特征,预测蛋白冠对植物造成的可能影响。结果表明：随着反应时间增加,纳米塑料的形貌变化越发明显,表现为尺寸和粗糙度的增加和稳定性的增...     

壳聚糖酶结构与功能的研究进展

壳聚糖酶是一类对壳聚糖具有较高催化活性而几乎不水解几丁质的糖苷水解酶,其可将高分子量的壳聚糖转化为低分子量的功能性壳寡糖。近年来,对壳聚糖酶的相关研究取得了显著进展,因此,本文对其生化性质、晶体结构、催化机制和蛋白质工程改造进行总结和探讨,并对酶法制备壳寡糖纯品进行展望,这将加深研究者对壳聚糖酶作用机制的认识,推动壳聚糖酶的工业应用。