Structure and energetics of ligand binding to proteins:Escherichia coli dihydrofolate reductase-trimethoprim, a drug-receptor system

1988 ◽  
Vol 4 (1) ◽  
pp. 31-47 ◽  
Author(s):  
Pnina Dauber-Osguthorpe ◽  
Victoria A. Roberts ◽  
David J. Osguthorpe ◽  
Jon Wolff ◽  
Moniqe Genest ◽  
...  
Keyword(s):  
Ligand Binding ◽  
Dihydrofolate Reductase ◽  
Receptor System ◽  
Drug Receptor

Role of Ionic Interactions in Ligand Binding and Catalysis of R67 Dihydrofolate Reductase†

Biochemistry ◽  
2003 ◽  
Vol 42 (36) ◽  
pp. 10569-10578 ◽  
Author(s):  
Stephanie N. Hicks ◽  
R. Derike Smiley ◽  
J. Bradley Hamilton ◽  
Elizabeth E. Howell
Keyword(s):  
Ligand Binding ◽  
Dihydrofolate Reductase ◽  
Ionic Interactions ◽  
R67 Dihydrofolate Reductase

scholarly journals An Inhibitory Region of the DNA-Binding Domain of Thyroid Hormone Receptor Blocks Hormone-Dependent Transactivation

1998 ◽  
Vol 12 (1) ◽  
pp. 34-44 ◽  
Author(s):  
Ying Liu ◽  
Akira Takeshita ◽  
Takashi Nagaya ◽  
Aria Baniahmad ◽  
William W. Chin ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Dna Binding ◽  
Ligand Binding ◽  
Transcriptional Activation ◽  
Thyroid Hormone Receptor ◽  
Binding Domain ◽  
Dna Binding Domain ◽  
Chimeric Receptor ◽  
Receptor System ◽  
Inhibitory Region

Abstract We have employed a chimeric receptor system in which we cotransfected yeast GAL4 DNA-binding domain/retinoid X receptor β ligand-binding domain chimeric receptor (GAL4RXR), thyroid hormone receptor-β (TRβ), and upstream activating sequence-reporter plasmids into CV-1 cells to study repression, derepression, and transcriptional activation. In the absence of T3, unliganded TR repressed transcription to 20% of basal level, and in the presence of T3, liganded TRβ derepressed transcription to basal level. Using this system and a battery of TRβ mutants, we found that TRβ/RXR heterodimer formation is necessary and sufficient for basal repression and derepression in this system. Additionally, an AF-2 domain mutant (E457A) mediated basal repression but not derepression, suggesting that interaction with a putative coactivator at this site may be critical for derepression. Interestingly, a mutant containing only the TRβ ligand binding domain (LBD) not only mediated derepression, but also stimulated transcriptional activation 10-fold higher than basal level. Studies using deletion and domain swap mutants localized an inhibitory region to the TRβ DNA-binding domain. Titration studies further suggested that allosteric changes promoting interaction with coactivators may account for enhanced transcriptional activity by LBD. In summary, our findings suggest that TR heterodimer formation with RXR is important for repression and derepression, and coactivator interaction with the AF-2 domain may be needed for derepression in this chimeric system. Additionally, there may be an inhibitory region in the DNA-binding domain, which reduces TR interaction with coactivators, and prevents full-length wild-type TRβ from achieving transcriptional activation above basal level in this chimeric receptor system.

scholarly journals Internalization of the interleukin 6 signal transducer gp130 does not require activation of the Jak/STAT pathway

1998 ◽  
Vol 330 (1) ◽  
pp. 47-54 ◽  
Author(s):  
Stefan THIEL ◽  
Iris BEHRMANN ◽  
Elke DITTRICH ◽  
Leon MUYS ◽  
Jan TAVERNIER ◽  
...  
Keyword(s):  
Ligand Binding ◽  
Interleukin 6 ◽  
Tyrosine Kinases ◽  
Receptor Tyrosine Kinases ◽  
Signal Transducer ◽  
Down Regulation ◽  
Receptor System ◽  
Stat Proteins ◽  
Receptor Mediated Endocytosis ◽  
Stat Pathway

Signalling receptors often undergo receptor-mediated endocytosis. In many cases this internalization is stimulated by ligand binding and activation of intrinsic receptor tyrosine kinases, resulting in a receptor down-regulation. We have analysed whether internalization of the interleukin 6 signal transducer gp130 is dependent on the activation of receptor-associated Jak kinases. By using a chimaeric receptor system we found that receptor mutants that lack box1 and therefore are not capable of activating Jak and signal transducer and activator of transcription (STAT) proteins are still endocytosed efficiently. A chimaeric receptor with the recently identified dileucine internalization motif being replaced by two alanine residues was not efficiently internalized but still capable of recruiting STATs. Furthermore an antagonistic antibody that inhibits the signalling of all interleukin-6-type cytokines via gp130 was internalized as efficiently as an agonistic one that activates the Jak/STAT pathway. Our findings suggest that the endocytosis of gp130 is signal-independent.

Studies on the mechanism of action of picrotoxinin and other convulsants at the crustacean muscle GABA receptor

1986 ◽  
Vol 227 (1247) ◽  
pp. 191-216 ◽  
Keyword(s):  
Gaba Receptor ◽  
Partial Agonist ◽  
Lateral Shift ◽  
Penicillin G ◽  
Ionic Selectivity ◽  
Receptor System ◽  
Crustacean Muscle ◽  
Drug Receptor ◽  
Antagonist Action ◽  
External Ph

The actions of picrotoxinin, bicuculline and penicillin-G were investigated on the GABA-receptor system of lobster muscle by using intracellular recording. The highly potent antagonist, picrotoxinin, produced a lateral shift and depression in the maximum of the GABA dose–conductance curve (designated as mixed antagonism); bicuculline, a weak antagonist, caused only a depression in the maximum with little or no lateral shift, whereas penicillin-G, an even weaker antagonist, produced a greater depression at the top of the dose–response curve. The possible sites of antagonist action were examined, with a critical re-evaluation of a drug-receptor model previously proposed to account for the antagonistic behaviour of picrotoxinin (the mixed antagonistic model); this model was extended to include the actions of bicuculline and penicillin-G. Antagonism was examined (i) towards different GABA receptor agonists; (ii) in various external anion media; (iii) at varying external pH; and (iv) when two different antagonists were combined. The GABA agonists were differentially antagonized by picrotoxinin and bicuculline, but external pH and substituent anions caused only minor perturbations to the inhibition. Combination experiments suggested at least three sites for GABA antagonists binding on crustacean muscle: (i) the GABA recog­nition site or sites; (ii) the ionic selectivity site in the ionophore; and (iii) a highly lipophilic site which may be part of the GABA receptor or ionophore. The mixed antagonism model accounted for the pH and external anion data but required modification to a cyclic scheme to explain the antagonism of a partial agonist. A model based on two-state receptor theory could only account for the antagonism of GABA if picrotoxinin was assumed not only to perturb L (the R ⇌ T conformation constant) but also to affect the agonist binding affinity. It is suggested that picrotoxinin and bicuculline may antagonize GABA responses by stabilizing the closed form of the activated channel, whereas penicillin-G may block the channel in the open state.

The galactose-specific receptor system in rat liver during development

Development ◽  
1987 ◽  
Vol 100 (1) ◽  
pp. 13-22
Author(s):  
L. Dini ◽  
L. Conti-Devirgiliis ◽  
S. Russo-Caia
Keyword(s):  
Endothelial Cells ◽  
Ligand Binding ◽  
Rat Liver ◽  
Binding Capacity ◽  
Specific Binding ◽  
Cell Types ◽  
Receptor System ◽  
In Situ Experiments

The number and distribution of galactose-specific binding sites were investigated in rat liver cells during perinatal development. Ligand binding to hepatocytes, macrophages and endothelial cells was followed with in vitro and in situ experiments by electron microscopy, using lactosylated bovine serum albumin adsorbed onto 5 nm colloidal gold particles as ligand. Binding capacity, starting at a late stage of fetal development, is very low both on the hepatocyte and on the macrophage surface, which show single particles statistically distributed. By contrast, bound particles are absent from fetal endothelial cells, which also lack the typical coated regions. In vivo, experiments at 37 degrees C show that endocytosis occurs to some extent in prenatal life. These results indicate that the expression of galactose-specific receptors' activity on the different liver cell types follows different developmental patterns, which are independently modulated.

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