Research progress in structure and function of pectin methylesterase / 生物工程学报

Pectin methylesterase (PME) is an important pectinase that hydrolyzes methyl esters in pectin to release methanol and reduce the degree of methylation of pectin. At present, it has broad application prospects in food processing, tea beverage, paper making and other production processes. With the in-depth study of PME, the crystal structures with different sources have been reported. Analysis of these resolved crystal structures reveals that PME belongs to the right-hand parallel β-helix structure, and its catalytic residues are two aspartic acids and a glutamine, which play the role of general acid-base, nucleophile and stable intermediate, in the catalytic process. At the same time, the substrate specificity is analyzed to understand the recognition mechanism of the substrate and active sites. This paper systematically reviews these related aspects.

Crystallography of ATP hydrolysis mechanism in rat brain kinesin / 生物工程学报

Rat brain kinesin is a conventional kinesin that uses the energy from ATP hydrolysis to walk along the microtubule progressively. Studying how the chemical energy in ATP is utilized for mechanical movement is important to understand this moving function. The monomeric motor domain, rK354, was crystallized. An ATP analog, AMPPNP, was soaked in the active site. Comparing the complex structure of rK354 x AMPPNP and that of rK354ADP, a hypothesis is proposed that Glu237 in the Switch II region sensors the presence of gamma-phosphate and transfers the signal to the microtubule binding region.

Expression, crystallization and crystallographic study of the 1st IgV domain of human CD96 / 生物工程学报

CD96 (Tactile) is an adhesion receptor expressed mainly on activated T cells, NK cells. As a family member of the immunoglobulin-like cell receptor, CD96 consists of three immunoglobulin-like domains (V1, V2/C and C) in the extracellular region. Recent studies have shown that the 1st IgV domain of CD96 (CD96V1) plays an essential role in cell adhesion and NK cell-mediated killing. In this study, the 1st IgV domain of human CD96 (hCD96V1) was cloned and expressed in Escherichia coli (BL21). The soluble protein was obtained by refolding of the hCD96V1 inclusion bodies. From analytical ultracentrifugation, we could predict that CD96 V1 maily exists as dimer with approximate molecular weight of 26.9 kDa. The protein was then successfully crystallized using the sitting-drop vapour-diffusion method. The crystals diffracted to 1.9 angstrom resolution and belonged to space group P21, with unit-cell parameters a = 35.1, b = 69.5, c = 49.6A, alpha=gamma=90 degrees, beta=105.4 degrees.

Estudo experimental do aquecimento adequado de solução cristaloide por micro-ondas e dedução de equação para seu cálculo / Experimental study of adequate microwave warming of crystalloids and derivation of an equation for calculating heating parameters", "_e": "n

INTRODUÇÃO: Fluidos cristaloides são comumente aquecidos em forno de micro-ondas, para uso endovenoso ou subcutâneo (em lipoaspirações). A literatura médica é pobre em trabalhos estabelecendo parâmetros científicos para esse processo. O objetivo deste estudo foi estudar experimentalmente o aquecimento de solução salina (cloreto de sódio a 0,9%), a partir de diferentes temperaturas iniciais, deduzir uma equação para permitir o cálculo de parâmetros de aquecimento e estudar o decréscimo de temperatura da solução aquecida. MÉTODO: Frascos para infusão endovenosa (500 ml e 1.000 ml) de solução salina tiveram sua temperatura inicial ajustada para 15°C, 20°C e 25°C, sendo aquecidos por micro-ondas até 60 segundos (500 ml) e 120 segundos (1.000 ml). A temperatura da solução salina foi medida durante e ao final do aquecimento e até 30 minutos após esse processo. A partir dos resultados, foi deduzida uma equação. RESULTADOS: O aquecimento por 60 segundos elevou a temperatura de frascos de 500 ml de solução salina em cerca de 20°C. Foram necessários 120 segundos para a mesma elevação de temperatura de frascos de 1.000 ml. A equação deduzida foi: TIF = TII + [0,165 x Tempo (segundos) / Volume (litros)], onde TIF = temperatura interna final e TII = temperatura interna inicial. Não foram encontradas diferenças significantes entre as temperaturas interna e externa após o aquecimento. CONCLUSÕES: A determinação da temperatura inicial é fundamental na obtenção da temperatura final desejada, após o aquecimento de fluidos cristaloides por micro-ondas. Uma equação pôde ser deduzida, tornando possível o cálculo da temperatura final a partir de várias temperaturas iniciais. A temperatura externa dos frascos reflete adequadamente sua temperatura interna.

BACKGROUND: Crystalloids are commonly heated in microwave ovens for intravenous or subcutaneous usage (e.g., in liposuction). However, few studies have empirically determined the parameters for this procedure. This study experimentally evaluated the heating of saline solution (sodium chloride 0.9%) at different initial temperatures to derive an equation to calculate heating parameters as well as the temperature decrease in saline solutions after heating. METHODS: The initial temperature of intravenous pouches containing saline solution (500 and 1,000 mL) was adjusted to 15°C, 20°C, or 25°C. The 500 and 1,000 mL pouches were then warmed in a microwave (900 W) for 60 and 120 seconds, respectively. The temperature of the saline solution was measured during heating and immediately and 30 minutes after heating. An equation was derived from the results. RESULTS: Warming the 500 and 1,000 mL pouches for 60 and 120 seconds, respectively, at 900 W increased the temperature of these pouches by 20°C. The derived equation was as follows: final temperature = initial temperature + [0.165 × time (s)/volume (L)]. No significant differences were found between the internal and external temperatures of the pouches after heating. CONCLUSIONS: Determining the initial temperature of crystalloid solutions is essential for obtaining the desired temperature after microwave warming. The equation derived in the present study enables calculation of the final temperature of solutions with various initial temperatures. The external temperature of the pouches accurately reflects their internal temperature.

The effect of cold-light-activated bleaching treatment on enamel surfaces in vitro / 国际口腔科学杂志·英文版

This in vitro study aims to evaluate the crystal and surface microstructure of dental enamel after cold-light bleaching treatment. Twelve sound human premolars were cross-split into four specimens, namely, mesio-buccal (Group LP), disto-buccal (Group P), mesio-lingual (Group NP) and disto-lingual (Group L) specimens. These four groups were treated using the standard cold-light bleaching procedure, a bleaching agent, a peroxide-free bleaching agent and cold-light, respectively. Before and after treatment, all specimens were analyzed by high-resolution, micro-area X-ray diffraction and scanning electron microscopy. Using a spectrometer, tooth color of all specimens was measured before and after treatment. The phase of the enamel crystals was identified as hydroxyapatite and carbonated hydroxyapatite. After treatment, specimens in Groups LP and P showed significantly weaker X-ray diffraction peaks, significant reduction in crystal size and crystallinity, significant increase in L* but decrease in a* and b*, and obvious alterations in the surface morphology. However, specimens in Groups NP and L did not show any significant changes. The cold-light bleaching treatment leads to demineralization in the enamel surface. The acidic peroxide-containing bleaching agent was the major cause of demineralization, whereas cold-light did not exhibit significant increase or decrease effect on this demineralization.

An evaluation of the mechanical properties of Type III and Type IV gypsum mixed with two disinfectant solutions.

Background and Objectives: This in-vitro study was conducted to evaluate the strength and properties of Type III and Type IV gypsum mixed with disinfectant solutions. Materials and Methods: Type III and Type IV gypsum were used for the study. Three different mixing solutions namely waterqueous solutions of 0.525% sodium hypochlorite and 2% glutaraldehyde were used. Gypsum materials were subjected to further modification by adding a mixture of 1.0% gum arabic and 0.132% calcium hydroxide before mixing with the disinfectant solutions, at two different liquid/powder (L/P) ratios for each. Both, the unmodified and the modified gypsum were tested for compressive and tensile strength after one hour and one week from the start of the mix. The crystalline configuration of the fracture fragments of the unmodified and modified set gypsum were studied under the scanning electron microscope. Results: The disinfectant solutions reduced the strength of both Type III and Type IV gypsum. Water showed higher-strength, which was followed by 0.525% sodium hypochlorite and 2% glutaraldehyde. The modified Type III and Type IV gypsum with reduced L/P ratio also showed strength values less than that of the control groups. Interpretation and Conclusion: Chemical disinfectants reduced the strength of gypsum when used as water substitutes. Gum Arabic and calcium hydroxide additives permitted lower L/P ratio, however, there was still excess water retained in the set gypsum that lowered the strength values of Type III and Type IV gypsum. Hence, further reduction of L/P ratio may increase the properties of the modified Type III and Type IV gypsum.

Expression and crystallographic studies of a fungal immunomodulatory protein LZ-8 from a medicinal fungus Ganoderma lucidum / 生物工程学报

LZ-8 protein, isolated from a well known Chinese traditional medicinal fungus Ganoderma lucidum, is the first member of fungal immunomodulatory protein, members of which have been isolated from a variety of medicinal and edible mushrooms in the last two decades. The protein plays a multifunctional and important role in modulating immune system. In this report, in order to get LZ-8 protein crystals, the LZ-8 gene was expressed and purified by affinity chromatography, gel filtration chromatography and anion exchange chromatography subsequently. The protein was then crystallized using the hanging-drop vapour-diffusion method. The LZ-8 crystals were obtained and the phase information was calculated by X-ray diffraction. The resolution of LZ-8 crystals is 3.2A. This study will provide an insight into the structure of fungal immunomodulatory proteins.

Comparative study on inorganic composition and crystallographic properties of cortical and cancellous bone / 生物医学与环境科学（英文）

<p><b>OBJECTIVE</b>To comparatively investigate the inorganic composition and crystallographic properties of cortical and cancellous bone via thermal treatment under 700 °C.</p><p><b>METHODS</b>Thermogravimetric measurement, infrared spectrometer, X-ray diffraction, chemical analysis and X-ray photo-electron spectrometer were used to test the physical and chemical properties of cortical and cancellous bone at room temperature 250 °C, 450 °C, and 650 °C, respectively.</p><p><b>RESULTS</b>The process of heat treatment induced an extension in the a-lattice parameter and changes of the c-lattice parameter, and an increase in the crystallinity reflecting lattice rearrangement after release of lattice carbonate and possible lattice water. The mineral content in cortical and cancellous bone was 73.2wt% and 71.5wt%, respectively. For cortical bone, the weight loss was 6.7% at the temperature from 60 °C to 250 °C, 17.4% from 250 °C to 450 °C, and 2.7% from 450 °C to 700 °C. While the weight loss for the cancellous bone was 5.8%, 19.9%, and 2.8 % at each temperature range, the Ca/P ratio of cortical bone was 1.69 which is higher than the 1.67 of stoichiometric HA due to the B-type CO₃²⁻ substitution in apatite lattice. The Ca/P ratio of cancellous bone was lower than 1.67, suggesting the presence of more calcium deficient apatite.</p><p><b>CONCLUSION</b>The collagen fibers of cortical bone were arrayed more orderly than those of cancellous bone, while their mineralized fibers ollkded similar. The minerals in both cortical and cancellous bone are composed of poorly crystallized nano-size apatite crystals with lattice carbonate and possible lattice water. The process of heat treatment induces a change of the lattice parameter, resulting in lattice rearrangement after the release of lattice carbonate and lattice water and causing an increase in crystal size and crystallinity. This finding is helpful for future biomaterial design, preparation and application.</p>

Bone response to biosilicates® with different crystal phases

The aim of this study was to investigate the histological and histomorphometrical bone response to three Biosilicates with different crystal phases comparing them to Bioglass®45S5 implants used as control. Ceramic glass Biosilicate and Bioglass®45S5 implants were bilaterally inserted in rabbit femurs and harvested after 8 and 12 weeks. Histological examination did not revealed persistent inflammation or foreign body reaction at implantation sites. Bone and a layer of soft tissue were observed in close contact with the implant surfaces in the medullary canal. The connective tissue presented few elongated cells and collagen fibers located parallel to implant surface. Cortical portion after 8 weeks was the only area that demonstrated significant difference between all tested materials, with Biosilicate 1F and Biosilicate 2F presenting higher bone formation than Bioglass®45S5 and Biosilicate® vitreo (p=0.02). All other areas and periods were statistically non-significant (p>0.05). In conclusion, all tested materials were considered biocompatible, demonstrating surface bone formation and a satisfactory behavior at biological environment.

O objetivo deste estudo foi investigar histologicamente e histomorfometricamente a resposta óssea a três diferentes fases cristalinas do Biosilicato®, comparando-os aos implantes de Bioglass®45S5 utilizados como controles. Implantes de cerâmicas de Biosilicato® e implantes de Bioglass®45S5 foram inseridos bilateralmente em fêmures de coelho e avaliações histológicas realizadas após 8 e 12 semanas. As avaliações histológicas não revelaram inflamação persistente ou reação de corpo estranho nos sítios de implantação dos biovidros. A formação de tecido ósseo pôde ser observada em maior quantidade na porção cortical, com tecido conjuntivo sendo observado em íntimo contato com as superfícies dos implantes apenas na porção medular. O tecido conjuntivo apresentou células com forma alongada e fibras de colágeno localizado paralelamente à superfície do implante. A porção cortical (após 8 semanas) foi a única área que demonstrou diferença significante entre os materiais estudados, com o Biosilicato 1F e o Biosilicato 2F demonstrando maior formação de tecido ósseo em contato com a superfície quando compardos aos implantes de Bioglass®45S5 e Biosilicato®vítreo (p=0,02). As outras áreas estudadas nos diferentes períodos não foram consideradas estatisticamente significantes (p>0,05). Pode-se concluir que todos os materiais testados foram considerados biocompatíveis, com formação óssea na superfície e comportamento em ambiente biológico satisfatório.

Desarrollo de la cristalografía estructural en el siglo XX. Su impacto en las ciencias biomédicas y las perspectivas en este campo / Structural Crystallography Development in the 20 th Century. Impact in the Biomedical Sciences and Perspectives in this Field

El desarrollo de la cristalografía estructural está estrechamente ligado a los avances en otras áreas de la ciencia y la tecnología: química, física y matemáticas, y a los adelantos en computación y robótica. Aunque el descubrimiento de los rayos X por Wilhelm Honrad Roentgen (1845-1923) tuvo lugar en 1895, el uso de la radiación en la determinación de la estructura de los cristales sólo se logró a partir del descubrimiento de Max von Laue (1876-1960), en 1912, según el cual un cristal expuesto a un haz de rayos X originaba sombras específicas. A partir de ese hecho, la estructura de cristales simples, como el cloruro de sodio y el diamante, fue determinada con el método de difracción de rayos X. Sin embargo, para moléculas complejas como las proteínas, que por sus medidas de peso molecular son catalogadas como macromoléculas, no fue fácil la determinación de su estructura tridimensional en esa época.

The development of structural crystallography is closely linked to advances in other areas of science and technology: chemistry, physics and mathematics, and to advances in computing and robotics. Although the discovery of X-rays by Wilhelm Honrad Roentgen (1845-1923) took place in 1895, the use of radiation in the determination of crystal structure was only achieved after the discovery by Max von Laue (1876-1960) in 1912 that a crystal exposed to an X-ray beam produced specific shadows. From that fact, the structure of single crystals, such as sodium chloride and diamond, was determined with the X-ray diffraction method. However, for complex molecules such as proteins, which are classified as macromolecules because of their molecular weight measurements, it was not easy to determine their three-dimensional structure at that time.

Preliminary study of homogeneous phase redeposition of dissolved dental subgingival calculus / 生物医学工程学杂志

Fresh dental calculus were scratched and rinsed with distilled water, and then dissolved by HNO3. Simulated body fluid was used as control. Aqueous ammonia was added to step up the pH. FSEM and FI-IR were used to analyze the crystal character of deposition. Turbid occurred when pH = 5.4 and deposition occurred when pH = 5.6. Ribbon-like crystal, which was the same as the crystal in natural dental calculus was observed in experimental group and was evidenced to be hydroxyapatite (HAP) by FT-IR. HAP formation through homogeneous phase redeposition of dissolved dental subgingival calculus may be related with the existing template molecules in dental subgingival calculus resolution, which induce the biomineralization of HAP formation.

Synthesis of chrysin derivatives and their interaction with DNA / 药学学报

Using chrysin as a leading compound, intermediate 5, 7-dihydroxy-6, 8-bis (hydroxymethyl) flavone (1) was synthesized by hydroxymethylation. The intermediate reacted with different alcohols to afford 5, 7-dihydroxy-6, 8-bis ( methoxymethyl) flavone (2), 6, 8-bis (ethoxymethyl) -5, 7dihydroxyflavone (3), 6, 8-bis-(butoxymethyl)-5, 7-dihydroxyflavone (4), 6, 8-bis (pentyloxymethyl) -5,7-dihydroxy flavone (5) and 6, 8-bis-(ethoxymethyl) -5-hydroxy-7-methoxyflavone (6). These compounds were characterized by IR, 1H NMR, 13C NMR and element analysis. The crystal structure of 6 was determined by X-ray crystal diffraction. The interaction of the derivatives with CT-DNA was studied by fluorescent spectroscopy. According to the Stern-Volmer equation, the quenching constants of the compounds 1 - 4 were measured, separately, they were K(q1) = 9.71 x 10(3) L x mol(-1), K(q2) = 2.25 x 10(4) L x mol(-1), K(q3) = 1.03 x 10(4) L x mol(-1) and K(q4) = 7.96 x 10(3) L x mol(-1). Compounds 1-4 showed higher binding affinity with DNA than chrysin did. The results provided the experimental basis for developing a more effective flavonoid and worthing further thoroughly study.

Microwave-induced fast decalcification of rat bone for electron microscopic analysis: an ultrastructural and cytochemical study

Bone decalcification is a time-consuming process. It takes weeks and preservation of the tissue structure depends on the quality and velocity of the demineralization process. In the present study, a decalcification methodology was adapted using microwaving to accelerate the decalcification of rat bone for electron microscopic analysis. The ultrastructure of the bone decalcified by microwave energy was observed. Wistar rats were perfused with paraformaldehyde and maxillary segments were removed and fixed in glutaraldehyde. Half of specimens were decalcified by conventional treatment with immersion in Warshawsky solution at 4ºC during 45 days, and the other half of specimens were placed into the beaker with 20 mL of the Warshawsky solution in ice bath and thereafter submitted to irradiation in a domestic microwave oven (700 maximum power) during 20 s/350 W/±37ºC. In the first day, the specimens were irradiated 9 times and stored at 40ºC overnight. In the second day, the specimens were irradiated 20 times changing the solution and the ice after each bath. After decalcification, some specimens were postfixed in osmium tetroxide and others in osmium tetroxide and potassium pyroantimonate. The specimens were observed under transmission electron microscopy. The results showed an increase in the decalcification rate in the specimens activated by microwaving and a reduction of total experiment time from 45 days in the conventional method to 48 hours in the microwave-aided method.

A preservação da estrutura de ossos é dependente da qualidade e da velocidade em que ocorre o processo de desmineralização. Neste estudo foi observada a ultraestrutura de maxila de rato descalcificada utilizando microondas. Ratos Wistar sofreram perfusão com paraformaldeído e o segmento de maxila retirado e fixado em glutaraldeído. Após esta etapa algumas amostras foram descalcificadas por imersão em solução de Warshawsky durante 45 dias a 4(0)C. Outras amostras foram submetidas a irradiação por microondas (forno de microondas doméstico 700 Watts de potência), durante 20 s/350 W/ ± 37ºC. No primeiro dia foram realizadas um total de 9 irradiações e os espécimes foram deixadas posteriormente a 4ºC por 12 h na solução descalcificadora sem agitação. No segundo dia, os fragmentos foram submetidos à nova irradiação totalizando 20 banhos, trocando-se a solução e o gelo a cada banho. A seguir algumas amostras foram pós-fixadas com tetróxido de ósmio e outras com tetróxido de ósmio e piroantimonato de potássio. As amostras foram observadas em microscópio eletrônico de transmissão. Os resultados mostraram que o processo de descalcificação ativado por microondas reduziu para 48 h o período de descalcificação, o qual pelo método tradicional ocorre em 45 dias.

Perspective for pharmaceutical innovation in Brazil - center for applied toxinology (CEPID- center for research, innovation and dissemination - FAPESP)

The Center for Applied Toxinology (CAT), an institutional research organization based at the Butantan Institute, is one of the several Centers of Research, Innovation and Dissemination (CEPID) created in September 1998. CEPID, a pioneering program of the The State of São Paulo Research Foundation (FAPESP), was established to stimulate research, disseminate knowledge and foster contact between science and industry. CAT aims at conducting research on compounds derived from naturally occurring toxins, which might be of medical, ecological and economic interest. CAT takes a multidisciplinary approach in the investigation of natural toxins, including isolation and purification, pharmacological action, structural determination, structure-function studies, and molecular biology aspects. The following institutions will be involved in this endeavor: University of São Paulo (USP) [Marine Biology Center; Departments of Physiology and Anatomy, Institute for Biomedical Sciences; Department of Biochemistry, Institute of Chemistry]; São Paulo State University (UNESP) [Laboratory of Structural Biology and Zoochemistry, Institute of Biosciences, Rio Claro; Laboratory of Crystallography, Department of Physics, Institute of Biosciences, Humanities, and Exact Sciences, São José do Rio Preto]; and the Federal University of São Paulo (UNIFESP).(AU)

Crystal structure of raw pure Mysore silk fibre based on (Ala-Gly)2-Ser-Gly peptide sequence using Linked-Atom-Least-Squares method.

We have carried out crystal structure analysis of raw pure Mysore silk fibers belonging to Bombyx mori on the basis of model parameters of Marsh et al using Linked-Atom-Least-Squares technique. The intensity of all the reflections were computed employing CCP13 software. We observe that the molecular modification is essentially same as b-pleated structure with antipolar-antiparallel arrangements formed by hydrogen bonds. The essential differences observed in the structure are highlighted and discussed.

Estudos estruturais de infestinas, inibidores de serinoprotewases do tipo /kazal, presentes no estômago do barbeiro Triatoma infestans / Structural studies of serine proteases inhibitors from the kissing bug Triatoma infestants

Animais hematófagos possuem uma necessidade vital em manter o sangue fluido, durante a aquisição, o armazenamento e digestão do alimento. Para tal, esses animais desenvolveram ao longo de seus processos evolutivos mecanismos para interferir na hemostasia dos seus hospedeiros. Foi identificado anteriormente no barbeiro Triatoma infestans vetor da doença de Chagas, um potente inibidor de trombina denominado infestina 1-2 esta proteína é codificada por um gene composto por sete domínios tipo Kazal, que possuem isoladamente diferentes atividades inibitórias para as serinoproteases plasmáticas. Esta proteína é provavelmente processada em inibidores menores compostos por 1 ou 2 domínios após a sua tradução por um mecanismo ainda desconhecido. Neste trabalho, identificou-se a presença de um potente inibidor de fator XIIa no estômago do barbeiro T. infestans correspondente aos domínios 3 e 4 do gene da infestina, confirmando a atividade inibitória sobre fator XIIa caracterizada na infestina 34 recombinante. Determinou-se ainda a estrutura tridimensional do domínio 1 de infestina em complexo com tripsina bovina a uma resolução de 2,5A. Foram analisadas as interações intramoleculares da infestina 1 responsáveis pela manutenção da estrutura do inibidor e também as interações entre as moléculas de infestina 1 e a tripsina. Adicionalmente, a infestina 4 foi clonada, expressa e a mesma apresentou características cinéticas semelhantes ao inibidor de fator XIIa nativo, inibindo não apenas fator XIIa (128 pM) mas também fator Xa (53 nM), plasmina (2,1 nM) e tripsina (11 nM). Finalmente, determinou-se a estrutura do domínio 4 da infestina a uma resolução de 1,8A ,1,73A e 1,4A. E a mesma apresentou as mesmas características estruturais de outros inibidores da família Kazal

Mecanismo molecular da ação do hormônio tireoideano / Molecular mechanism of thyroid hormone action

Os hormônios tireoideanos (HTs) são necessários para a diferenciação, crescimento e metabolismo de diversos tecidos de vertebrados. Seus efeitos são mediados pelos receptores do hormônio tireoideano (TRs), membros da superfamília dos receptores nucleares. Estes receptores são fatores de transcrição modulares que se ligam em seqüências específicas do DNA denominadas elementos responsivos ao TR, que são encontrados nos promotores dos genes regulados pelo HT. Os TRs são codificados por dois genes distintos, alfae beta, localizados nos cromossomos 17 e 3, respectivamente. Estas isoformas apresentam diferentes funções e sua expressão é específica para cada tecido. O TR se liga ao DNA como monômero, homodímero ou heterodímero com o receptor de retinóide X (RXR). Além disso, o TR modula a atividade transcricional (repressão ou ativação) através da interação com correpressores e co-ativadores, na ausência e na presença do T3, respectivamente. A compreensão do mecanismo molecular da ação do receptor do hormônio tireoideano e a definição de sua estrutura cristalográfica contribuirão para a aquisição de novos conceitos envolvidos na transcrição e nos distúrbios hormonais presentes nas doenças endócrinas, assim como facilitará o desenho de novas drogas, agonistas ou antagonistas, com grande valor terapêutico.

Enhancement of catalytic activity of enzymes by heating in anhydrous organic solvents: 3D structure of a modified serine proteinase at high resolution.

For the first time, it is demonstrated that exposure of an enzyme to anhydrous organic solvents at optimized high temperature enhances its catalytic power through local changes at the binding region. Six enzymes, namely, proteinase K, wheat germ acid phosphatase, alpha-amylase, beta-glucosidase, chymotrypsin and trypsin were exposed to acetonitrile at 70 degrees C for three hr. The activities of these enzymes were found to be considerably enhanced. In order to understand the basis of this change in the activity of these enzymes, proteinase K was analyzed in detail using X-ray diffraction method. The overall structure of the enzyme was found to be similar to the native structure in aqueous environment. The hydrogen bonding system of the catalytic triad remained intact after the treatment. However, the water structure in the substrate binding site underwent some rearrangement as some of the water molecules were either displaced or completely absent. The most striking observation concerning the water structure was the complete deletion of the water molecule which occupied the position at the so-called oxyanion hole in the active site of the native enzyme. Three acetonitrile molecules were found in the present structure. All the acetonitrile molecules were located in the recognition site. Interlinked through water molecules, the sites occupied by acetonitrile molecules were independent of water molecules. The acetonitrile molecules are involved in extensive interactions with the protein atoms. The methyl group of one of the acetonitrile molecules (CCN1) interacts simultaneously with the hydrophobic side chains of Leu 96, Ile 107 and Leu 133. The development of such a hydrophobic environment at the recognition site introduced a striking conformation change in Ile 107 by rotating its side chain about C alpha-C beta bond by 180 degrees to bring about the delta-methyl group within the range of attractive van der Waals interactions with the methyl group of CCN1. A similar change had earlier been observed in proteinase K when it was complexed to a substrate analogue, lactoferrin fragment.

Structural basis of DNA flexibility.

It has been recently shown by us, on the basis of crystal structure database that the flexibility of B-DNA double helices depends significantly on their base sequence. Our model building studies further indicated that the existence of bifurcated cross-strand hydrogen bonds between successive base pairs is possibly the main factor behind the sequence directed DNA flexibility. These cross-strand hydrogen bonds are, of course, weaker than the usual Watson-Crick hydrogen bonds and their bond geometry is characterized by relatively larger bond lengths and smaller bond angles. We have tried to improve our model structures by incorporating non-planarity of the amino groups in DNA bases due to the presence of lone pair electrons at the nitrogen atoms. Energy minimization studies have been carried out by using different quantum chemical methods, whereby it is found that in all cases of N-H....O type cross-strand hydrogen bonds, the bond geometry improves significantly. In the cases of N-H....N type hydrogen bonds, however, no such consistent improvements can be noticed. Perhaps the true picture would emerge only if all the other interactions present in the DNA macromolecule could be appropriately taken into account.

Galectinas: estructura, especificidad glicídica y ligandos específicos / Galectins: structure, sugar specificity and specific ligands

Las galectinas se definen por dos propiedades: secuencias de aminoácidos características compartidas y afinidad por azúcares ß-galactosídicos. Numerosas galactinas de mamíferos fueron secuenciadas y bien caracterizadas en diferentes especies, siendo clasificadas como galectina-1 a galectina-10, según sus homologías de secuencia. La identidad entre dominios que ligan carbohidratos de distintas galectinas de una especie de mamífero oscila entre 20-40 por ciento, mientras que la identidad de galectina-1, por ejemplo, entre distintas especies es de 80-90 por ciento. En la presente revisión, se describen las principales propiedades distintivas de las galectinas de mamífero en cuanto a estructura proteica, estructura cristalina, especificidad glicídica y ligandos específicos