1,720,958 research outputs found
Binding of Streptococcus pyogenes to laminin
No full textSome strains of Streptococcus pyogenes isolated from infected human tissues were shown to bind laminin, a major component of basement membranes. Binding of 125I-laminin to bacteria was time dependent and functionally irreversible. Of several unlabeled proteins tested in competition experiments, laminin and fibrinogen inhibited binding of the radiolabeled protein. The inhibitory effect exerted by fibrinogen was apparently not caused by a binding to the laminin receptors. The number of receptors available for laminin on cells of the strain examined ranged from 0 to 10(3) depending on the media used to grow the bacteria and an apparent KD of 4 X 10(-8)M was calculated for the reaction. Bacterial cells incubated with proteolytic enzymes lose the ability to bind laminin, and a trypsin digest contained active receptors capable of competing with intact cells for 125I-laminin. Active receptors may be adsorbed on a column of laminin-Sepharose but not on Sepharose gels substituted with fibrinogen or fibronectin. After radiolabeling the proteins in the trypsin digest a laminin-binding 125I-labeled protein (Mr greater than 10(6] was isolated by affinity chromatography from a receptor positive strain. Similar components could not be isolated from a strain apparently lacking laminin receptors. Therefore, this protein was tentatively identified as a laminin receptor of streptococci
Fibronectin binding to a Streptococcus pyogenes strain
No full textIn previous studies, Staphylococcus aureus has been shown to bind fibronectin (P. Kuusela, Nature (London) 276:718-720, 1978), an interaction that may be important in bacterial attachment and opsonization. Recently some strains of streptococci of serological groups A, C, and G were also found to bind fibronectin. The binding to one selected strain of Streptococcus pyogenes has been characterized here. The binding of [125I]fibronectin to streptococcal cells resembles that to staphylococcal cells and was found to be time dependent, functionally irreversible, and specific in the sense that unlabeled proteins other than fibronectin did not block binding. Bacteria incubated with proteases largely lost their ability to bind fibronectin, and material released from the streptococci by a brief trypsin digestion contained active fibronectin receptors. This material inhibited the binding of [125I]fibronectin to the streptococci. The inhibitory activity was adsorbed on a column of fibronectin-Sepharose but not on a column of unsubstituted Sepharose 4B or egg albumin Sepharose. The receptor appeared to be a protein nature since the inhibitory activity of the trypsinate was destroyed by papain and was not absorbed on a column containing monoclonal antibodies directed against lipoteichoic acid bound to protein A-Sepharose. Binding sites in fibronectin for streptococci and staphylococci, respectively, were localized by analyzing the ability of isolated fragments to inhibit [125I]fibronectin binding to bacteria and by adsorbing 125I-labeled tryptic fragments with staphylococcal and streptococcal cells. Both species of bacteria appeared to preferentially bind a fragment (Mr = approximately 25,000) originating from the N-terminal region of the protein. In addition, streptococci also bound a slightly smaller fragment (Mr = approximately 23,000). Fibronectin receptors solubilized from either streptococci or staphylococci inhibited the binding of fibronectin to both species of bacteria
Fibronectin receptors from Staphylococcus aureus
No full textFibronectin which is recognized for its ability to mediate
substrate adhesion of eucaryotic cells has also
been shown to bind to Staphylococcus aureus (Kuusela,
P. (1978) Nature (Lond)2 76, 718-720). A further characterization
of the interaction of fibronectin with
staphylococci is presented here. The binding of 1251-
fibronectin to S. aureus, strain Cowan 1, is specific,
time-dependent, functionally irreversible, and occurs
to both live and heat-killed cells. Furthermore, staphylocci
may be saturated with fibronectin at a level which
suggests the presence of 250 receptors/cell. A lysate
produced by digestion of staphylococcal cells with a
bacteriolytic enzyme (lysostaphin) inhibited the binding
of 125I-fibronectin to bacteria. The lysate was depleted
of its inhibitory activity by passage through a
column of Sepharose substituted with fibronectin. The
inhibitory activity was destroyed when the lysate was
incubated with trypsin or pronase, and a lysate prepared
from trypsin-treated cells did not have inhibitory
activity. These data suggest that the inhibitory activity
of the lysate is due to solubilized surface proteins acting
as receptors for fibronectin. Staphylococcal mutants
that selectively had lost protein A or fibronectin receptors
could be isolated, which suggests the presence of
fibronectin receptors distinctly different from protein
A. Externally 125 I-labeled proteins from the different
mutants were analyzed by affinity chromatography on
fibronectin-Sepharose followed by gel electrophoresis.
The fibronectin receptor was tentatively identified as
a protein with an apparenMt , = 18,000. This component
was found in fibronectin-binding strains but was absent
in strains deficient in fibronectin receptors
Binding of the basement membrane protein laminin to Escherichia coli
No full textHere, we report that strains of
uropathogenic E. coli bind to the basement membrane
protein laminin. Laminin, which is a glycoprotein
with Mr - 900 000 serves as a substrate
mediating the attachment and spreading of different
eucaryotic cellsbasement membrane
protein laminin
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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