1,720,976 research outputs found
G-protein sinyal ileti mekanizmalarına yapısal bir yaklaşım: Alfa altbirimi
No full textGuanin nükletit bağlayıcı proteinler duyusal algılama, protein sentezi, hormonal düzenleme, salgı kesecikleri ve çekirdek taşınımı, hücre büyümesi ve farklılaşmasını da içine alan birçok fizyolojik sürecin düzenlenmesinde rol oynarlar. Bu proteinler (GDP)-bağlı dinlenim durumuyla (GTP)-bağlı aktif durumları arasında bir döngü geçirerek moleküler aracılık görevlerini yerine getirirler. G-proteinleri 3 altbirimden oluşmaktadır: α, β, γ. G-proteininin özgünlüğü α altbirimi tarafından belirlenir. α-altbirimi de iki bölgeden oluşur: GTPaz bölgesi ve α-heliks bölgesi. Aktivasyon GTPaz bölgesindeki anahtar I, II ve III olarak adlandırılan bölgelerde yapısal değişikliklere yol açar. Hem reseptör hem de efektörlerle etkileşimde karboksil ucunun önemli olduğu gösterilmiştir.Guanine nucleotide binding proteins regulate a variety of physiological processes, including sensual perception, protein synthesis, hormonal regulation, vesicular and nuclear transport, cell growth and differentiation. They act as molecular mediators, cycling between inactive guanosine diphosphate (GDP)-bound and active guanosine triphosphate (GTP)-bound states. G-proteins are composed of three subunits: α, β, γ, where specificity mainly determined by α.The α-subunit consists of two domains: GTPase domain and α-helical domain. Activation results in conformational changes around so called switch I, II and III regions in GTPase- domain. Interaction of the receptor with the carboxyl terminus of α is clearly important. Carboxy terminus is also shown to be important in effector interaction
Determination of functional regions of human DAT for labeling with fluorescent proteins for further use in fret studies
No full textDopamin taşıyıcıları presinaptik uçtan salınan dopaminin sinaptik boşluktan geri alınarak (uptake) dopaminerjik sinyalin sonlandırılmasında çok önemli rol oynarlar. Bu çalışmada 12 zarı kateden bölge içeren bir zar proteini olan insan dopamin taşıyıcısının çeşitli bölgelerine eCFP proteininin yerleştirilmesi ve etiketli proteinlerin işlevsel durumunun saptanması amaçlandı. eCFP proteini, insan DAT proteinin N-ucu bölgesine ve 515 ve 587.amino asitlerin bulunduğu bölgelere takıldı. Böylelikle, bir sonraki aşamada gerçekleştirilecek FRET analizlerinde kullanılabilecek pozisyonlar belirlenmiş olacaktır. Gerialım testleri yalnızca N-ucu bölgesinin işlevsel olduğunu, p515 ve p587 bölgelerinin ise yaban tiple benzer ilginlikte olmalarına rağmen geri alım hızlarının çok düşük olduğunu gösterdi. Bu sonuç mikroskopla elde edilen yüzey ekspresyonu sonuçları ile de doğrulandı. eCFP proteinine eklenen esnek bağlaç dizileri de bu sonucu değiştirmedi.The dopamine transporter tightly regulates dopamine neurotransmission by the rapid uptake of released dopamine back into the presynaptic nerve terminal. This study aimed to determine functional positions for eCFP insertion into the human dopamine transporter, a membrane protein with 12 transmembrane domains. eCFP has been inserted into the N-terminus of human DAT and at positions 515 and 587. This will reveal available regions for further FRET analyses. Uptake assays showed that only the N-terminus is functional, while the other two positions exhibit extremely low rate of transport, even though their affinities are close to the wild type. These results were supported by surface expression profile observed on the microscope. Linker sequences attached to the terminals of eCFP did not change this pattern
FRET-based characterization of K264A, D345A, and Y335A mutants in the human dopamine transporter
No full text0The dopamine transporter (DAT) plays a role in the termination of dopaminergic neurotransmission; thereby it is accepted as the primary target of various psychostimulants. N-terminal phosphorylation of DAT has been proposed as a regulator in different DAT functions, such as amphetamine-induced efflux or PKC/PKA-mediated responses. To understand the role of N-terminal conformational changes in dopamine transporter structure and function, the fluorescence resonance energy transfer (FRET) method was applied to various DAT constructs fluorescently labeled at the N-terminus and substrate-induced conformational changes were determined using rhodamine-labeled cocaine analog JHC1-64 in three DAT mutants. The results indicated that the construct with YFP inserted into the N-terminal position-55 displayed effective interaction with the substrate and simultaneous mutation of two serine residues (S7 and S12) to alanine or aspartic acid demonstrated similar phenotypes as their wild-type (WT) counterparts. FRET was detectable for N-terminal p55 YFP WT, Ser/Ala, and Ser/Asp forms, but there was no significant difference among the three mutants, contrary to our expectations based on the previously proposed roles of these serine residues. In addition, three mutants (K264A, D345A, and Y335A) implemented in the position-55 YFP background were also investigated and the importance of Y335 in the translocation cycle and in the process of substrate release was verified
Dopamin taşıyıcıların kokain bağlama bölgesi ile N-ucu arasındaki uzaysal yakınlığının FRET ile belirlenmesi
No full textAmaç: Dopamin taşıyıcılar (DAT) dopaminin sinaptik gerialımından ve böylelikle sinirsel iletinin çabuk sonlanmasından sorumludur. Bu proteinler alışkanlık yapıcı kokain, amfetamin gibi maddelerin de etki merkezlerini oluşturur. Proteinin N-ucunda bulunan Serin 7 ve 12'nin fosforilasyon bakımından kritik amino asitler olduğu bilinmektedir. Bu çalışmada N-ucu ile kokain bağlama bölgesi arasındaki uzaklık, yaban tip ve Ser7/12Asp ve Ser7/12Ala mutantlarında belirlenmiştir.Gereç ve Yöntem: Sarı-floresan protein (YFP) ve mutasyonlar DAT'ın N-terminal ucuna 2-aşamalı PCR ile yerleştirilmiştir. Dopamin geri-alım testleri yapılmış ve konfokal mikroskopta verici-ağartma yöntemi ile Förster rezonans enerji transferi (FRET) mesafeleri belirlenmiştir. bulgular: Tüm N-ucundan YFP-etiketlenmiş DAT proteinleri düzgün olarak hücre yüzeyine taşınmıştır. K değerleri sırasıyla yaban tip, Ser7/12Ala and Ser7/12/Asp mutantları için 0.76, 0.75 ve 1.24 mM olarak saptanmıştır. FRET etkinliği yaban-tip DAT için 0.15 olarak bulunmuş ve FRET uzaklığı 68.4 Å olarak bulunmuştur. Diğer konstraktlarda FRET etkinlikleri negatiftir ve enerji transferi saptanmamıştır.Objective: The dopamine transporter (DAT) mediates uptake of dopamine from the synaptic cleft and provides rapid termination of neurotransmission. It is the site of action for different drugs of abuse, including cocaine and amphetamine. Serine 7 and 12 at the N-terminus were found to be critical residues in phosphorylation. Here, we addressed spatial proximity site relationship of N-terminal extension with respect to cocaine binding in wild type and Ser7/12Asp and Ser7/12Ala mutants. Materials and Methods: The yellow-fluorescent protein (YFP) and mutations were introduced into the N-terminus of the hSynDAT by a two-step PCR. Dopamine uptake assays were performed and Förster resonance energy transfer (FRET) distances were determined using donor bleach method in a confocal microscope.results: All N-terminally YFP-tagged DAT constructs were properly trafficked to the cell surface. K values were 0.76, 0.75 and 1.24 mM for wild-type, Ser7/12Ala and Ser7/12/Asp constructs, respectively. FRET efficiency value was found to be 0.15 for YFP-labeled DAT while corresponding estimated distance was calculated as 68.4 Å. FRET efficiencies of other constructs were negative and no energy transfer was detected
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
- …
