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Immunoglobulin-like modules from titin I-band: Extensible components of muscle elasticity
No full textBACKGROUND:
The giant muscle protein titin forms a filament which spans half of the sarcomere and performs, along its length, quite diverse functions. The region of titin located in the sarcomere I-band is believed to play a major role in extensibility and passive elasticity of muscle. In the I-band, the titin sequence consists mostly of repetitive motifs of tandem immunoglobulin-like (Ig) modules intercalated by a potentially non-globular region. The highly repetitive titin architecture suggests that the molecular basis of its mechanical properties be approached through the characterization of the isolated components of the I-band and their interfaces. In the present paper, we report on the structure determination in solution of a representative Ig module from the I-band (I27) as solved by NMR techniques.
RESULTS:
The structure of I27 consists of a beta sandwich formed by two four-stranded sheets (named ABED and A'GFC). This fold belongs to the intermediate frame (I frame) of the immunoglobulin superfamily. Comparison of I27 with another titin module from the region located in the M-line (M5) shows that two loops (between the B and C and the F and G strands) are shorter in I27, conferring a less elongated appearance to this structure. Such a feature is specific to the Ig domains in the I-band and might therefore be related to the functions of the protein in this region. The structure of tandem Ig domains as modeled from I27 suggests the presence of hinge regions connecting contiguous modules.
CONCLUSIONS:
We suggest that titin Ig domains in the I-band function as extensible components of muscle elasticity by stretching the hinge regions
When a module is also a domain: The role of the N terminus in the stability and the dynamics of immunoglobulin domains from titin
No full textIn the course of a structural study of titin, a giant modular protein from muscle, we have reported that N-terminal extension of immunoglobulin-like (Ig-like) domains from titin stabilizes this fold. In order to investigate the structural basis of such an effect, we have solved the structure of NEXTM5, which has six amino acids added to the sequence of M5, a domain for which full structure determination has been previously achieved. In the present work, the structures and the dynamics of M5 and NEXTM5 are compared in the light of data collected for these and other titin domains. In NEXTM5, three out of the six added residues are structured and pack against the nearby BC and FG loops. As a consequence, three new backbone hydrogen bonds are formed with the B strand, extending the A strand by two residues and decreasing the exposed surface area of the loops. Additional contacts which involve the side-chains give rise to a remarkable pH dependence of the stability. Interestingly, no correlation is observed on the NMR time-scale between the overall dynamics of the extended domain and its increased stability. The most noticeable differences between the two constructs are localised around the N terminus, which becomes more rigid upon extension. Since a similar pattern of contacts is observed for other domains of the immunoglobulin I-set, our results are of general relevance for this protein family. Our work might also inspire a more rational approach to the investigation of domain boundaries and their influence on module stability
The prehistoric site of Capo Zafferano (Sicily): Geomorphology and Holocene sea level variations
No full textA deposit of mollusk shell remains (Patella ferruginea and Trochus sp.) associated with stone artefacts (weapons, scrap-ers, etc.) of Mesolithic age, has been identified in an underwater cave (-20 m s.I.) at Capo Zafferano, a carbonatic promontory with steep cliffs 10 km E of Palermo (NW Sicily). Patella ferruginea samples are radiocarbon dated to 8960±130 yr B.P. calibrated to 9350÷9900 yr BP in agreement with archaeological dating. Underwater investigations indicate submerged terraces, at -16÷18 m below present sea-level, forming a continuous strip around the promontory and which provided access to the cave. Sea-level at 9500 yr B.P. at the site was about 25 m below the present level: this datum is in agreement with the Tyrrhenian Holocene sea-level curve
Attività tettonica recente nel massiccio del Pollino suggerita dallo studio di speleotemi fratturati
No full textFractures or anomalies along the growth axis of spelaeothems may yield valuable information on suspected tectonically active regions, when more conventional deformation markers are absent. Radiometric dating of deformed spelaeothems provides a record of continuous motion, once the tectonic nature of deformation has been assessed. Deformed spelaeothems were collected in caves of an about 20 km long stretch of the southern border of the Pollino carbonate Massif, in Northern Calabria (Southern Italy). Contrary to conterminous regions, lack of evidence of active tectonics and significant historical seismicity induced to consider this area seismically quiescent. The cave systems are aligned along-strike of a through-going fault system (Pollino Line), where recent paleoseismoiogical investigations indicated late Pleistocene and Holocene earthquake-induced slips. The investigated caves exhibit a very recent transition from phreatic to vadose conditions and are tectonically displaced from their primary spelaeo-genic and morphologic setting. This suggests a differential uplift of the carbonate block and a recent tectonic sinking of the karst base-level. At least two growing generations of spelaeothems have been distinguished on a morphological and structural basis. A recurrent east-southeast shift of growth axes of younger spelaeothems was observed in all sites, which is consistent with the overall Quaternary kinematics of this region and also of the Crati area which is more to the South. Preliminary dating indicates activity in the late Pleistocene (40 ka) and Holocene. The lack of concretion growth observed between about 40 ka and 10 ka might be preliminarily related to a reduced water supply during the glacial maximum. This is consistent with observations in continental Europe and North America, but differs from the nearby sites of the Tyrrhenian coast of Italy so as to suggest periglacial conditions at low-moderate elevations near the sea in the Pollino Massif
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
When a module is also a domain: The role of the N terminus in the stability and the dynamics of immunoglobulin domains from titin
No full textIn the course of a structural study of titin, a giant modular protein from muscle, we have reported that N-terminal extension of immunoglobulin-like (Ig-like) domains from titin stabilizes this fold. In order to investigate the structural basis of such an effect, we have solved the structure of NEXTM5, which has six amino acids added to the sequence of M5, a domain for which full structure determination has been previously achieved. In the present work, the structures and the dynamics of M5 and NEXTM5 are compared in the light of data collected for these and other titin domains. In NEXTM5, three out of the six added residues are structured and pack against the nearby BC and FG loops. As a consequence, three new backbone hydrogen bonds are formed with the B strand, extending the A strand by two residues and decreasing the exposed surface area of the loops. Additional contacts which involve the side-chains give rise to a remarkable pH dependence of the stability. Interestingly, no correlation is observed on the NMR time-scale between the overall dynamics of the extended domain and its increased stability. The most noticeable differences between the two constructs are localised around the N terminus, which becomes more rigid upon extension. Since a similar pattern of contacts is observed for other domains of the immunoglobulin I-set, our results are of general relevance for this protein family. Our work might also inspire a more rational approach to the investigation of domain boundaries and their influence on module stability
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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