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The two faces of Janus: Functional interactions and protein aggregation
No full textProtein aggregation constitutes a constant threat for the living cell as is demonstrated by the several pathologies in which the mechanisms to prevent it fail. It is therefore a question of increasing importance to understand in detail the defence strategies. Here we discuss how molecular interactions can represent a general strategy to prevent aggregation. This view generalizes the more specific paradigm that suggests a competition between folding and aggregation, and allows to include both intrinsically unfolded proteins and proteins that aggregate also under native conditions. We analyze the factors that influence the balance between the two competing pathways and suggest new perspectives to increase our understanding of misfolding pathologies
Model ligands for copper proteins. Proton magnetic resonance study of acetylhistamine and acetylhistidine complexes with copper(I)
No full textThe complexes (acetylhistamine)2copper+ and (acetyl-L-histidine)2copper+ have been studied in aqueous solutions by means of proton magnetic resonance spectroscopy. The amide group proved to be unable to complex Cu+ both alone and in conjunction with the nonspecific imidazole ligand. The Cu2+ specific carboxylate group, on the other hand, appears to be a possible site of coordination also for Cu+ when coupled with the imidazole ligand. These results are interpreted with respect to the problem of the active site of copper proteins with redox activity
Conformational changes of aspartate induced by high salt concentrations
No full textThe conformational changes of aspartate induced by increasing ionic strength were investigated by means of NMR spectroscopy. The effects of Li, Na, K and Cs chlorides in basic solutions show a relative stabilization of the two conformers with gauche carboxylates at the expense of the anti conformer. A significant quantitative difference was found between Na+ and K+. The changes observed in neutral solutions, although larger than those in basic solutions, are dominated by the zwitterion interaction
Influence of the ionic environment on the conformation of aspartic acid and possible relevance to its neurotransmitter action
No full textUnderstanding the binding properties of an unusual metal-binding protein - A study of bacterial frataxin
No full textDeficiency of the small mitochondrial protein frataxin causes Friedreich's ataxia, a severe neurodegenerative pathology. Frataxin, which has been highly conserved throughout evolution, is thought to be involved in, among other processes, Fe-S cluster formation. Independent evidence shows that it binds iron directly, although with very distinct features and low affinity. Here, we have carried out an extensive study of the binding properties of CyaY, the bacterial ortholog of frataxin, to different divalent and trivalent cations, using NMR and X-ray crystallography. We demonstrate that the protein has low cation specificity and contains multiple binding sites able to chelate divalent and trivalent metals with low affinity. Binding does not involve cavities or pockets, but exposed glutamates and aspartates, which are residues that are unusual for iron chelation when not assisted by histidines and/or cysteines. We have related how such an ability to bind cations on a relatively large area through an electrostatic mechanism could be a valuable asset for protein function
Understanding the binding properties of an unusual metal-binding protein - A study of bacterial frataxin
No full textDeficiency of the small mitochondrial protein frataxin causes Friedreich's ataxia, a severe neurodegenerative pathology. Frataxin, which has been highly conserved throughout evolution, is thought to be involved in, among other processes, Fe-S cluster formation. Independent evidence shows that it binds iron directly, although with very distinct features and low affinity. Here, we have carried out an extensive study of the binding properties of CyaY, the bacterial ortholog of frataxin, to different divalent and trivalent cations, using NMR and X-ray crystallography. We demonstrate that the protein has low cation specificity and contains multiple binding sites able to chelate divalent and trivalent metals with low affinity. Binding does not involve cavities or pockets, but exposed glutamates and aspartates, which are residues that are unusual for iron chelation when not assisted by histidines and/or cysteines. We have related how such an ability to bind cations on a relatively large area through an electrostatic mechanism could be a valuable asset for protein function
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
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