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  • 1995-1999  (5)
  • 1
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: FK506 (tacrolimus) is a natural product now approved in the US and Japan for organ transplantation. FK506, in complex with its 12 kDa cytosolic receptor (FKBP12), is a potent agonist of immunosuppression through the inhibition of the phosphatase activity of calcineurin. Rapamycin (sirolimus), which is itself an immunosuppressant by a different mechanism, completes with FK506 for binding to FKBP12 and thereby acts as an antagonist of calcineurin inhibition. We have solved the X-ray structure of unliganded FKBP12 and of FKBP12 in complex with FK506 and with rapamycin; these structures show localized differences in conformation and mobility in those regions of the protein that are known, by site-directed mutagenesis, to be involved in calcineurin inhibition. A comparison of 16 additional X-ray structures of FKBP12 in complex with FKBP12-binding ligands, where those structures were determined from different crystal forms with distinct packing arrangements, lends significance to the observed structural variability and suggests that it represents an intrinsic functional characteristic of the protein. Similar differences have been observed for FKBP12 before, but were considered artifacts of crystal-packing interactions. We suggest that immunosuppressive ligands express their differential effects in part by modulating the conformation of FKBP12, in agreement with mutagenesis experiments on the protein, and not simply through differences in the ligand structures themselves.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: We have synthesized a series of non-macrocyclic ligands to FKBP12 that are comparable in binding potency and peptidyl prolyl isomerase (PPIase) inhibition to FK506 itself. We have also solved the structure of one of these ligands in complex with FKBP12, and have compared that structure to the FK506–FKBP12 complex. Consistent with the observed inhibitory equipotency of these compounds, we observe a strong similarity in the conformation of the two ligands in the region of the protein that mediates PPIase activity. Our compounds, however, are not immunosuppressive. In the FKBP12–FK506 complex, a significant portion of the FK506 ligand, its `effector domain', projects beyond the envelope of the binding protein in a manner that is suggestive of a potential interaction with a second protein, the calcium-dependent phosphatase, calcineurin, whose inhibition by the FKBP 12–FK506 complex interrupts the T-cell activation events leading to immunosuppression. In contrast, our compounds bind within the surface envelope of FKBP12, and induce significant changes in the structure of the FKBP12 protein which may also affect calcineurin binding indirectly.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of industrial microbiology and biotechnology 19 (1997), S. 157-157 
    ISSN: 1476-5535
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Archives of virology 144 (1999), S. 1345-1360 
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary.  Virion sense gene replacement derivatives of maize streak virus (MSV) were constructed with selectable marker expression cassettes based on the bialaphos resistance gene (bar) and the CaMV 35S promoter. The effect on replication of increasing the genomic size was tested by including: (1) the 550-bp maize adh I intron and 68-bp TMV Ω RNA leader sequences upstream of the bar genes; and (2) a fusion between the bar and E. coli glutathione reductase (gor) genes. Three recombinant viral vectors ranging in size from 2.7 kb to 4.8 kb replicated efficiently in biolistically transfected cells of suspension cultured Black Mexican sweetcorn (BMS) cells. Deletions greater than 39 bp 3′ of the stemloop sequence in the LIR adversely affected replicon release. Transformed bialaphos-resistant BMS cell lines were generated with all three vectors containing the bar gene: between 38 and 60% of cell lines contained replicating viral episomes. The replicons were structurally stable, replicated to copy numbers of over 500 per haploid genome, and were detected for more than one year after introduction. We noted significant enhancement of bar gene expression, both at the protein and RNA levels, associated with the presence of episomal vector DNA. The maize adhI intron and TMV Ω RNA leader sequences did not seem to have a significant effect on bar gene expression from replicating constructs, although expression from controls was enhanced. The results suggest that MSV-based constructs would provide a useful system for long-term gene amplification in cereal cell culture systems.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1617-4623
    Keywords: Key wordsClostridium ; Aryl-β-glucoside ; PTS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A phosphotransferase-dependent aryl-β-glucoside uptake and utilisation system (abg) was isolated from the ruminal Clostridium (“C. longisporum”). The system is composed of three genes, abgG, abgF and abgA, and a number of regulatory regions, including terminator/antiterminator type stem-loop structures preceding the abgG and abgF genes. Similarity analysis of the proteins encoded by these genes indicated that they were responsible for the regulation of the abg system through antitermination (AbgG), the uptake and phosphorylation of aryl-β-glucosides (AbgF) and the hydrolysis of the intracellular phosphorylated glycosides (AbgA). Experimental evidence for the functions of AbgF and AbgA was obtained. Although it was not possible to demonstrate any function for AbgG, a promoter 5′ to the abgG gene was identified which was responsible for expression of the downstream genes. The abg system is remarkably similar to operons from the gram negative Enterobacteriaceae, both in the coding and non-coding regulatory regions.
    Type of Medium: Electronic Resource
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