1,721,117 research outputs found
Stationary and time-dependent carbon monoxide stretching mode features in carboxy myoglobin: a theoretical-computational reappraisal
Full text linkThe stationary and time-dependent infrared spectrum (IR) of the CO stretching mode (νCO) in carboxymyoglobin (MbCO), a longstanding problem of biophysical chemistry, has been modeled through a theoretical-computational method specifically designed for simulating quantum observables in complex atomic-molecular systems and based on a combined application of long time scale molecular dynamics simulations and quantum-chemical calculations. This study is basically focused on two aspects: (i) the origin of the stationary IR substates (termed as A0, A1, and A3) and (ii) the modeling and the interpretation of the νCO energy relaxation. The results, strengthened by a more than satisfactory agreement with the experimental data, concisely indicate that (i) the conformational His64-FeCO relevant substates, i.e., characterized by the formation-disruption of the H-bond between the above moieties, are the main responsible of the presence of two distinct and well separated (A0 and A1/A3) spectroscopic regions; (ii) the characteristic bimodal shape of the A1/A3 spectral region, according to our model, is the result of the fluctuation of the electric field pattern as provided by the protein-solvent framework perturbing the bound His64-CO-Heme complex; and (iii) the electric field pattern, in conjunction with the relatively high density of MbCO vibrational states, is also the main determinant of the νCO energy relaxation, characterizing its kinetic efficiency
The unfolding effects on the protein hydration shell and partial molar volume: A computational study
No full textIn this paper we apply the computational analysis recently proposed by our group to characterize the solvation properties of a native protein in aqueous solution, and to four model aqueous solutions of globular proteins in their unfolded states thus characterizing the protein unfolded state hydration shell and quantitatively evaluating the protein unfolded state partial molar volumes. Moreover, by using both the native and unfolded protein partial molar volumes, we obtain the corresponding variations (unfolding partial molar volumes) to be compared with the available experimental estimates. We also reconstruct the temperature and pressure dependence of the unfolding partial molar volume of Myoglobin dissecting the structural and hydration effects involved in the process
In vitro preferential topoisomerization of bent DNA.
No full textThe steps of the topoisomerization reaction by calf thymus DNA topoisomerase I on a DNA domain containing an intrinsically bent DNA sequence have been analyzed. High preferentiality of binding, cleavage and topoisomerization on the bent segment relative to the rest of the DNA domain was observed. These studies show the importance of the local DNA conformation in the reaction of eukaryotic DNA topoisomerase I and the interest of the use of this enzyme as a tool for the analysis of DNA conformation and DNA dynamics
The conformation of constitutive DNA interaction sites for eukaryotic DNA topoisomerase I on intrinsically curved DNAs.
No full textThe analysis of the sites which are cleaved constitutively and preferentially by eukaryotic DNA topoisomerase I on two intrinsically curved DNAs reveals the conformational features that provoke the cleavage reaction on the curve-inducing sequence elements in the absence of supercoiling. This analysis is based on the observation (Caserta et al. (1989) Nucleic Acids Res. 17, 8521-8532 and (1990) Biochemistry 29, 8152-8157) that the reaction of eukaryotic DNA topoisomerase I occurs on two types of DNA sites: sites S (Supercoiled induced) and sites C (Constitutive, whose presence is topology-independent). We report that sites C are abundant on the intrinsically curved DNAs analyzed. The DNAs studied were two intrinsically curved segments of different origin: the Crithidia fasciculata kinetoplast DNA and the bent-containing domain B of the Saccharomyces cerevisiae ARS1. On these DNA segments DNA topoisomerase I cleaves at the junctions between the poly(A) tracts and mixed-sequence DNA. Analysis of the conformation of the double helix around the cleavage sites has revealed that the reaction occurs in correspondence of a defined DNA conformational motif. This motif is described by the set of Eulerian angular values that define the axial path of DNA (helical twist, deflection angle, direction) and of the orthogonal components of wedge (roll and tilt)
A first principles polarizable water model for molecular simulations: application to a water dimer
No full textn this paper we describe a new Hamiltonian model for polarizable water, whose reliability should in principle be independent of system dimension. Such a model is largely based on first principles using the charge density expansion and linear polarizability to treat intermolecular interactions. A semi-empirical function is added only to describe short-range atomic repulsions. The accuracy of this method has been evaluated comparing the results of our model with highly correlated quantum chemical calculations (CCSD(T)) performed on a system of two interacting water molecules. Results show that this model provides a rather accurate description of the system studied. © 2002 Elsevier Science B.V. All rights reserved
Density discriminates between thermophilic and mesophilic proteins
No full textDespite an intense interest and a remarkable number of studies on the subject, the relationships between thermostability and (primary, secondary and tertiary) structure of proteins are still not fully understood. Here, comparing the protein density - defined by the ratio between the residue number and protein excluded volume - for a set of thermophilic/mesophilic pairs, we provide evidence that this property is connected to the optimal growth temperature. In particular, our results indicate that thermophilic proteins have - in general - a lower density with respect to the mesophilic counterparts, being such a correlation more pronounced for optimal growth temperature differences greater than 40° C. The effect of the protein thermostability changes on the molecular shape is also presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
