1,721,032 research outputs found
Peptide self-assembly at the nanoscale: a challenging target for computational and experimental biotechnology
No full textSelf-assembly at the nanoscale is becoming increasingly important for
the fabrication of novel supramolecular structures, with applications in
the fields of nanobiotechnology and nanomedicine. Peptides represent the
most favorable building blocks for the design and synthesis of
nanostructures because they offer a great diversity of chemical and
physical properties, they can be synthesized in large amounts, and can
be modified and decorated with functional elements, which can be used in
diverse applications. In this article, we review some of the most recent
experimental advances in the use of nanoscale self-assembled peptide
structures and the theoretical efforts aimed at understanding the
microscopic determinants of their formation, stability and
conformational properties. The combination of experimental observations
and theoretical advances will be fundamental to fully realizing the
biotechnological potential of peptide self-organization
The molecular dynamics of assembly of the ubiquitous aortic medial amyloidal medin fragment
No full textIn recent years there is an increased understanding of the molecular
conformation of amyloid fibrils. However, much less is known about the
early events that lead to the formation of these medically important
assemblies. The clarification of these very important mechanistic
details on the process may indicate directions towards the inhibition of
the early stages of the assembly, where harmful species are most likely
to form. Here, we study the dynamics of assembly of short amyloidogenic
peptide fragments from the medin polypeptide. This polypeptide is of
unique interest since amyloid deposits composed of medin are found
almost in all the population above the age of 50. Twelve independent 50
ns long molecular dynamics simulations in explicit water have been run
on peptide NH2-NFGSVQFV-COOH, the minimal recognition hexapeptide
element, NH2-NFGSVQ-COOH, and several single-point mutants. In all cases
a three-stranded polymeric P-sheet was used as the basic unit from which
fibrils can be formed. Our results clearly indicate the need of
well-defined sequence and stereochemical constraints to allow the
formation of stable well-ordered aggregates. One of the key findings is
the need for the presence of a phenylalanine residue, but not other
hydrophobic amino acids, in specific positions within the peptide. Taken
together, the results are consistent with recent high-resolution
structures of amyloid assemblies and provide unique insights into the
dynamics of these structures. (c) 2006 Elsevier Inc. All rights
reserved
Entropically-Driven Co-assembly of l-Histidine and l-Phenylalanine to Form Supramolecular Materials
No full textMolecular self-and co-assembly allow the formation of diverse and well-defined supramolecular structures with notable physical properties. Among the associating molecules, amino acids are especially attractive due to their inherent biocompatibility and simplicity. The biologically active enantiomer of L-histidine (L-His) plays structural and functional roles in proteins but does not self-assemble to form discrete nanostructures. In order to expand the structural space to include L-His-containing materials, we explored the co-assembly of L-His with all aromatic amino acids, including phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp), all in both enantiomeric forms. In contrast to pristine L-His, the combination of this building block with all aromatic amino acids resulted in distinct morphologies including fibers, rods, and flake-like structures. Electrospray ionization mass spectrometry (ESI-MS) indicated the formation of supramolecular co-assemblies in all six combinations, but time-of-flight secondary-ion mass spectrometry (ToF-SIMS) indicated the best seamless co-assembly occurs between L-His and L-Phe while in the other cases, different degrees of phase separation could be observed. Indeed, isothermal titration calorimetry (ITC) suggested the highest affinity between L-His and L-Phe where the formation of co-assembled structures was driven by entropy. In accordance, among all the combinations, the co-assembly of L-His and L-Phe produced single crystals. The structure revealed the formation of a 3D network with nanocavities stabilized by hydrogen bonding between-N (L-His) and-NH (L- Phe). Taken together, using the co-assembly approach we expanded the field of amino acid nanomaterials and showed the ability to obtain discrete supramolecular nanostructures containing L-His based on its specific interactions with L-Phe
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
Variations on the Author
Get PDF“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
Get PDFWe 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
- …
