Bruton's tyrosine kinase associates with the actin-based cytoskeleton in activated platelets

Bruton's tyrosine kinase (Btk) plays a crucial role in the maturation and differentiation of B-lymphocytes and immunoglobulin synthesis. Recently Btk has been described to be present in significant amount in human platelets. To investigate the regulation of this kinase in the platelets we studied its subcellular redistribution in the resting and activated cells. In the resting platelets Btk was almost absent from the actin-based cytoskeleton. Upon challenge of the platelet thrombin receptor upto 30% of total Btk appeared in the cytoskeleton and the protein underwent phosphorylation on tyrosine. Translocation of Btk to the cytoskeleton but not aggregation was prevented by cytochalasin B, which inhibits actin polymerization. Wortmannin and genistein (inhibitors of phosphoinositide 3-kinase and protein tyrosine kinase, respectively) decreased while phenylarsine oxide (a tyrosine phosphatase inhibitor) increased the cytoskeletal content of Btk. The association of Btk with the cytoskeleton was regulated by integrin α<SUB>IIb</SUB>β<SUB>3</SUB> and partly reversible. Taken together, these data suggest that Btk might be a component of a signaling complex containing specific cytoskeletal proteins in the activated platelets. J. Cell. Biochem. 81: 659–665, 2001. © 2001 Wiley-Liss, Inc

Regulation of postaggregation events induced by protease-activated receptor 1 ligation in human platelets: evidence of differential signaling pathways

In a physiological milieu platelets continue to be exposed to agonists long after clot formation. We studied the regulation of postaggregation events consequent on protease-activated receptor (PAR) 1 ligation with either thrombin or the thrombin receptor-activating peptide (TRAP). Stimulation with TRAP (20 μM) but not with thrombin (1 U/ml) for 15 min evoked platelet disaggregation by about 30% and downregulation of high-affinity fibrinogen binding sites on integrin αIIbβ3 to nearly prestimulation levels. Concurrently, only TRAP disorganized the actin-based cytoskeleton, with decrease in the cytoskeletal content of focal contact-associated proteins like integrin αIIbβ3, Src, and focal adhesion kinase (FAK). While protein tyrosine kinases were activated during the initial period of platelet aggregation with either agonist, stimulation of protein tyrosine phosphatases determined the successive phase of reduced phosphotyrosine content. SHP-1, an abundant protein tyrosine phosphatase in the platelets, was tyrosine phosphorylated on challenge of PAR-1 and coprecipitated with two unidentified tyrosine phosphorylated proteins of 140 and 60 kDa; in addition, SHP-1 tyrosine phosphorylation (which is associated with enhanced phosphatase activity) was sustained until 15 min. Activity of calpain was upregulated following incubation with thrombin and not with TRAP. Collectively, these data suggest that signaling pathways elicited by PAR-1 agonists thrombin and TRAP are markedly different, which could have important implications on late platelet responses

Synthesis, glycosidase inhibitory activity and computational studies of dideoxymethylnojirimycin and its derivatives

We report here the synthesis and biological evaluation of dideoxynojirimycin and its analogs and their functional effect on glucosidase enzyme inhibition against α-glucosidase(yeast), α-galactosidase and β-galactosidase (kluyveromyces lactis). All the compounds significantly inhibited the α-glucosidase(yeast) activity when compared to DNJ and shown strong inhibition against β-galactosidase (kluyveromyces lactis) when compared to DNJ. The molecular docking studies also reveals that these compounds showing strong ligand binding energies against yeast-ɑ-glucosidase- I, yeast β-galactosidase and human lysosomal acid–ɑ-glucosidase. Interestingly the analogues having N-H, N-alkyl and N-benzyl group along with ethyl group significantly inhibited the β-galactosidase activity when compared to DNJ. The in-silico studies are in correlation with invitro activity data; therefore, this study will be useful to develop further glycosidase inhibitors

Human proteinpedia enables sharing of human protein data

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A manually curated functional annotation of the human X chromosome

Since the human genomic sequence first became publicly available1, 2, almost all annotations of individual chromosomes have been carried out by the groups involved in the sequencing. We carried out a detailed annotation of the human X chromosome using data generated by the Sanger Institute and other centers (obtained from ftp.sanger.ac.uk/pub/sequences/human/Chr_X). Here, we report the salient features of our analysis of its genome, transcriptome and proteome..

Human protein reference database as a discovery resource for proteomics

The rapid pace at which genomic and proteomic data is being generated necessitates the development of tools and resources for managing data that allow integration of information from disparate sources. The Human Protein Reference Database (http://www.hprd.org) is a web-based resource based on open source technologies for protein information about several aspects of human proteins including protein–protein interactions, post-translational modifications, enzyme–substrate relationships and disease associations. This information was derived manually by a critical reading of the published literature by expert biologists and through bioinformatics analyses of the protein sequence. This database will assist in biomedical discoveries by serving as a resource of genomic and proteomic information and providing an integrated view of sequence, structure, function and protein networks in health and disease

Development of Human Protein Reference Database as an Initial Platform for Approaching Systems Biology in Humans

Human Protein Reference Database (HPRD) is an object database that integrates a wealth of information relevant to the function of human proteins in health and disease. Data pertaining to thousands of protein-protein interactions, posttranslational modifications, enzyme/substrate relationships, disease associations, tissue expression, and subcellular localization were extracted from the literature for a nonredundant set of 2750 human proteins. Almost all the information was obtained manually by biologists who read and interpreted >300,000 published articles during the annotation process. This database, which has an intuitive query interface allowing easy access to all the features of proteins, was built by using open source technologies and will be freely available at http://www.hprd.org to the academic community. This unified bioinformatics platform will be useful in cataloging and mining the large number of proteomic interactions and alterations that will be discovered in the postgenomic era