1,720,980 research outputs found
Anatomy of an iron-sulfur cluster scaffold protein: Understanding the determinants of [2Fe-2S] cluster stability on IscU.
No full textProtein-bound iron sulfur clusters are prosthetic groups involved in several metabolic pathways. Understanding how they interact with the host protein and which factors influence their stability is therefore an important goal in biology. Here, we have addressed this question by studying the determinants of the 2Fe-2S cluster stability in the IscU/Isu protein scaffold. Through a detailed computational study based on a mixed quantum and classical mechanics approach, we predict that the simultaneous presence of two conserved residues, D39 and H105, has a conflicting role in cluster coordination which results in destabilizing cluster-loaded IscU/Isu according to a 'tug-of-war' mechanism. The effect is absent in the D39A mutant already known to host the cluster more stably. Our theoretical conclusions are directly supported by experimental data, also obtained from the H105A mutant, which has properties intermediate between the wild-type and the D39A mutant. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases
The quantum mechanically mixed-spin state in a non-symbiotic plant hemoglobin: The effect of distal mutation on AHb1 from Arabidopsis thaliana
No full textCoexistence of multiple globin genes conferring protection against nitrosative stress to the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125
No full textIbuprofen induces an allosteric conformational transition in the heme complex of human serum albumin with significant effects on heme ligation
No full textHuman serum albumin (HSA), the most prominent protein in blood plasma, is able to bind a
wide range of endogenous and exogenous compounds. Among the endogenous ligands, HSA is a significant
transporter of heme, the heme-HSA complex being present in blood plasma. Drug binding to heme-HSA
affects allosterically the heme affinity for HSA and vice versa. Heme-HSA, heme, and their complexes
with ibuprofen have been characterized by electronic absorption, resonance Raman, and electron
paramagnetic resonance (EPR) spectroscopy. Comparison of the results for the heme and heme-HSA
systems has provided insight into the structural consequences on the heme pocket of ibuprofen binding.
The pentacoordinate tyrosine-bound heme coordination of heme-HSA, observed in the absence of
ibuprofen, becomes hexacoordinate low spin upon ibuprofen binding, and heme dissociates at increasing
drug levels. The electronic absorption spectrum and ν(Fe-CO)/ν(CO) vibrational frequencies of the
CO-heme-HSA-ibuprofen complex, together with the observation of a Fe-His Raman mode at 218 cm-1
upon photolysis of the CO complex and the low spin EPR g values indicate that a His residue is one of the
low spin axial ligands, the sixth ligand probably being Tyr161. The only His residue in the vicinity of the
heme Fe atom is His146, 9 Å distant in the absence of the drug. This indicates that drug binding to
heme-HSA results in a significant rearrangement of the heme pocket, implying that the conformational
adaptability of HSA involves more than the immediate vicinity of the drug binding site. As a whole, the
present spectroscopic investigation supports the notion that HSA could be considered as the prototype of
monomeric allosteric proteins
Extended cardiolipin anchorage to cytochrome c: a model for protein-mitochondrial membrane binding
No full textTwo models have been proposed to explain the interaction of cytochrome c with cardiolipin (CL) vesicles. In one case, an acyl chain of the phospholipid accommodates into a hydrophobic channel of the protein located close the Asn52 residue, whereas the alternative model considers the insertion of the acyl chain in the region of the Met80-containing loop. In an attempt to clarify which proposal offers a more appropriate explanation of cytochrome c-CL binding, we have undertaken a spectroscopic and kinetic study of the wild type and the Asn52Ile mutant of iso-1-cytochrome c from yeast to investigate the interaction of cytochrome c with CL vesicles, considered here a model for the CL-containing mitochondrial membrane. Replacement of Asn52, an invariant residue located in a small helix segment of the protein, may provide data useful to gain novel information on which region of cytochrome c is involved in the binding reaction with CL vesicles. In agreement with our recent results revealing that two distinct transitions take place in the cytochrome c-CL binding reaction, data obtained here support a model in which two (instead of one, as considered so far) adjacent acyl chains of the liposome are inserted, one at each of the hydrophobic sites, into the same cytochrome c molecule to form the cytochrome c-CL complex
The 40s Omega-loop plays a critical role in the stability and the alkaline conformational transition of cytochrome c
No full text
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
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