scholarly journals Participation of the Lys313-Ile333 Sequence of the Purinergic P2X4 Receptor in Agonist Binding and Transduction of Signals to the Channel Gate

2006 ◽  
Vol 281 (43) ◽  
pp. 32649-32659 ◽  
Author(s):  
Zonghe Yan ◽  
Zhaodong Liang ◽  
Tomas Obsil ◽  
Stanko S. Stojilkovic
Keyword(s):  
Transmembrane Domain ◽  
Critical Role ◽  
Receptor Function ◽  
Agonist Binding ◽  
Channel Opening ◽  
Channel Gate ◽  
Agonist Concentration ◽  
Opening And Closing ◽  
Kinetics Of

To study the roles of the Lys313-Ile333 ectodomain sequence of the rat P2X4 receptor in ATP binding and transduction of signals to the channel gate, the conserved Lys313, Tyr315, Gly316, Ike317, Arg318, Asp320, Val323, Lys329, Phe330, and Ile333 residues were mutated. Current recordings were done on lifted cells and ATP was applied using an ultrafast solution-switching system. The rates of wild type channel opening and closing in the presence of ATP, but not the rate of washout-induced closing, were dependent on agonist concentration. All mutants other than I317A were expressed in the plasma membrane at comparable levels. The majority of mutants showed significant changes in the peak amplitude of responses and the EC50 values for ATP. When stimulated with the supramaximal (1.4 mm) ATP concentration, mutants also differed in the kinetics of their activation, deactivation, and/or desensitization. The results suggest a critical role of the Lys313 residue in receptor function other than coordination of the phosphate group of ATP and possible contribution of the Tyr315 residue to the agonist binding module. The pattern of changes of receptor function by mutation of other residues was consistent with the operation of the Gly316-Ile333 sequence as a signal transduction module between the ligand binding domain and the channel gate in the second transmembrane domain.

Desensitization and resensitization rates of glutamate-activated channels may regulate motoneuron excitability

1991 ◽  
Vol 66 (4) ◽  
pp. 1166-1175 ◽  
Author(s):  
D. O. Smith ◽  
C. Franke ◽  
J. L. Rosenheimer ◽  
F. Zufall ◽  
H. Hatt
Keyword(s):  
Ampa Receptors ◽  
Single Channel ◽  
Kainate Receptors ◽  
Whole Cell ◽  
Solution Exchange ◽  
Channel Opening ◽  
Fast Solution ◽  
Agonist Concentration ◽  
Kinetics Of ◽  
Channel Properties

1. Single-channel properties of desensitizing glutamate-activated channels were analyzed in outside-out patch-clamp recordings from a motoneuron-enriched cell fraction from embryonic chick. A piezo-driven device was used to achieve fast solution exchange at the electrode tip, resulting in maximum activation within 2 ms. 2. Quisqualate/AMPA receptors, with a 13-pS conductance, desensitized rapidly; the desensitization rate depended on agonist concentration but not on membrane potential. When quisqualate was applied slowly, the quisqualate-activated channels desensitized without prior channel opening, indicating desensitization from the closed state. After a 10-ms refractory period, resensitization of all channels required up to 300 ms; resensitization rate did not depend on the duration of the preceding quisqualate application. 3. At agonist concentrations less than or equal to 1 mM, kainate receptors, with a 20-pS conductance, did not desensitize. At kainate concentrations greater than or equal to 1 mM, though, kainate receptors desensitized to a low steady-state conductance within approximately 200 ms. Resensitization of all channels required as long as 3 s, which could render kainate receptors inexcitable during high-frequency activation. 4. Desensitization rates of whole-cell currents were similar to those observed in outside-out mode. Glutamate- and quisqualate-activated responses were similar, suggesting that the rapidly desensitizing quisqualate-sensitive receptor type may dominate the kinetics of whole-cell excitatory postsynaptic currents (EPSCs) in this preparation. 5. It may be concluded that the efficacy of glutamate-mediated synaptic transmission is modulated by differences in the rates of desensitization and resensitization.

scholarly journals Role of the Second Extracellular Loop of Human C3a Receptor in Agonist Binding and Receptor Function

1999 ◽  
Vol 274 (14) ◽  
pp. 9721-9728 ◽  
Author(s):  
Ta-Hsiang Chao ◽  
Julia A. Ember ◽  
Meiying Wang ◽  
Yolanda Bayon ◽  
Tony E. Hugli ◽  
...  
Keyword(s):  
Receptor Function ◽  
Agonist Binding ◽  
Extracellular Loop

scholarly journals Structure of APP-C991-99 and Implications for Role of Extra-Membrane Domains in Function and Oligomerization

2018 ◽  
Author(s):  
George A. Pantelopulos ◽  
John E. Straub ◽  
D. Thirumalai ◽  
Yuji Sugita
Keyword(s):  
Transmembrane Domain ◽  
Chemical Shifts ◽  
Membrane Surface ◽  
Critical Role ◽  
Amyloid Formation ◽  
Cytoplasmic Proteins ◽  
C Terminus ◽  
N Terminus ◽  
Thin Membranes

AbstractThe 99 amino acid C-terminal fragment of Amyloid Precursor Protein APP-C99 (C99) is cleaved by γ-secretase to form Aβ peptide, which plays a critical role in the etiology of Alzheimer’s Disease (AD). The structure of C99 consists of a single transmembrane domain flanked by intra and intercellular domains. While the structure of the transmembrane domain has been well characterized, little is known about the structure of the flanking domains and their role in C99 processing by γ-secretase. To gain insight into the structure of full-length C99, REMD simulations were performed for monomeric C99 in model membranes of varying thickness. We find equilibrium ensembles of C99 from simulation agree with experimentally-inferred residue insertion depths and protein backbone chemical shifts. In thin membranes, the transmembrane domain structure is correlated with extra-membrane structural states. Mean and variance of the transmembrane and G37G38 hinge angles are found to increase with thinning membrane. The N-terminus of C99 forms β-strands that may seed aggregation of Aβ on the membrane surface, promoting amyloid formation. The N-terminus, which forms α-helices that interact with the nicastrin domain of γ-secretase. The C-terminus of C99 becomes more α-helical as the membrane thickens, forming structures that may be suitable for binding by cytoplasmic proteins, while C-terminal residues essential to cytotoxic function become α-helical as the membrane thins. The heterogeneous but discrete extra-membrane domain states analyzed here open the path to new investigations of the role of C99 structure and membrane in amyloidogenesis.

scholarly journals The Cortical Changes on Fertilization of the Sea-Urchin Egg

1955 ◽  
Vol 32 (3) ◽  
pp. 451-467
Author(s):  
H. KACSER
Keyword(s):  
Calcium Ions ◽  
Sea Urchins ◽  
Critical Role ◽  
Psammechinus Miliaris ◽  
Sea Urchin Egg ◽  
Dark Ground ◽  
Artificial Activation ◽  
Kinetics Of ◽  
Cortical Change

The kinetics of the dark ground cortical change in fertilized sea urchins has been analysed. In normal eggs of Psammechinus miliaris the change appears to obey an autocatalytic mechanism. The evidence from artificial activation suggests that the initiation of the response is caused by a relatively unspecific event. The critical role of calcium is considered in relation to the evidence from eggs fertilized in capillary tubes. This suggests that calcium ions are not concerned with the initiation but with the propagation of the response. The primary change in activation may consist of an increase in permeability at the site of initiation.

scholarly journals The Critical Role of Carbon in the Chemical Delithiation Kinetics of LiFePO4

2020 ◽  
Vol 167 (7) ◽  
pp. 070538 ◽  
Author(s):  
Montserrat Galceran ◽  
Abdelbast Guerfi ◽  
Michel Armand ◽  
Karim Zaghib ◽  
Montse Casas-Cabanas
Keyword(s):  
Critical Role ◽  
Kinetics Of

Relevant role of Leu265 in helix VI of the angiotensin AT1 receptor in agonist binding and activity

2002 ◽  
Vol 80 (5) ◽  
pp. 426-430 ◽  
Author(s):  
Silvana Aparecida Alves Correa ◽  
Lucimar Pereira França ◽  
Claudio Miguel Costa-Neto ◽  
Laerte Oliveira ◽  
Antonio Cechelli Mattos Paiva ◽  
...  
Keyword(s):  
Angiotensin Ii ◽  
Ligand Binding ◽  
Binding Affinity ◽  
Transmembrane Domain ◽  
Inositol Phosphate ◽  
Chinese Hamster ◽  
Side Chain ◽  
Maximum Effect ◽  
Agonist Binding

The finding of critical residues for angiotensin II (AII) binding and receptor signalling in helices V and VI led us to assess if, in this region of the receptor, aliphatic side chains might play a role in the agonist-mediated mechanism. Two mutations of the angiotensin AT1 receptor were designed to explore a possible role of a leucine at two positions, Leu265 and Leu268. Thus two mutants, L265D and L268D, were prepared through single substitutions of Leu265, located in the C-terminal region of transmembrane VI (TM-VI), and Leu268, in the adjoining region of the third extracellular loop (EC-3), for an aspartyl residue, and were stably transfected into Chinese hamster ovary (CHO) cells. Ligand-binding experiments and the functional assays determining inositol phosphate (IP) production were performed in these cells expressing these mutants. No significant changes were found in the binding affinity for the ligands, AII, DuP753, and [Sar1Leu8]AII in the mutant L268D. Moreover, the relative potency and the maximum effect on IP production of this mutant were similar to those of the wild-type receptor. In contrast, L265D mutant AT1 receptor, located within the transmembrane domain, markedly decreased binding affinity and ability to stimulate phosphatidylinositol turnover. Our results suggest that the hydrophobic side chain of Leu265, at the C-terminal portion of the AT1's TM-VI, but not Leu268, which belongs to the EC-3 loop, might interact with the AII molecule. On the other side, the aliphatic side chain of Leu265 may be involved in the formation of the ligand binding sites through allosteric effects, thus helping to stabilize the receptor structure around the agonist binding site for full activity.Key words: angiotensin II, AT1 receptor, site-directed mutagenesis.

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