scholarly journals The high-affinity calcium–calmodulin-binding site does not play a role in the modulation of type 1 inositol 1,4,5-trisphosphate receptor function by calcium and calmodulin

2002 ◽  
Vol 365 (3) ◽  
pp. 659-667 ◽  
Author(s):  
Elena NOSYREVA ◽  
Tomoya MIYAKAWA ◽  
Zhengnan WANG ◽  
Lyuba GLOUCHANKOVA ◽  
Akiko MIZUSHIMA ◽  
...  
Keyword(s):  
Binding Site ◽  
Lipid Bilayers ◽  
Expression System ◽  
Planar Lipid Bilayers ◽  
Wild Type ◽  
Direct Role ◽  
Mammalian Expression ◽  
High Affinity ◽  
Inositol 1,4,5 Trisphosphate

Modulation of the inositol 1,4,5-trisphosphate (InsP3) receptors (InsP3R) by cytosolic calcium (Ca2+) plays an essential role in Ca2+ signalling, but structural determinants and mechanisms responsible for the InsP3R regulation by Ca2+ are poorly understood. In the present study, we expressed rat InsP3R type 1 (InsP3R1) in Spodoptera frugiperda cells using a baculovirus-expression system and reconstituted the recombinant InsP3R1 into planar lipid bilayers for functional analysis. We observed only minor effects of 0.5mM of calmodulin (CaM) antagonist W-7 on the Ca2+ dependence of InsP3R1. Based on a previous analysis of mouse InsP3R1 [Yamada, Miyawaki, Saito, Nakajima, Yamamoto-Hino, Ryo, Furuichi and Mikoshiba (1995) Biochem J. 308, 83–88], we generated the Trp1577→Ala (W1577A) mutant of rat InsP3R1 which lacks the high-affinity Ca2+—CaM-binding site. We found that the W1577A mutant displayed a bell-shaped Ca2+ dependence similar to the wild-type InsP3R1 in planar lipid bilayers. Activation of B cell receptors resulted in identical Ca2+ signals in intact DT40 cells lacking the endogenous InsP3R and transfected with the wild-type InsP3R1 or the W1577A mutant cDNA subcloned into a mammalian expression vector. In the planar lipid bilayer experiments, we showed that both wild-type InsP3R1 and W1577A mutant were equally sensitive to inhibition by exogenous CaM. From these results, we concluded that the interaction of CaM with the high-affinity Ca2+—CaM-binding site in the coupling domain of the InsP3R1 does not play a direct role in biphasic modulation of InsP3R1 by cytosolic Ca2+ or in InsP3R1 inhibition by CaM.

scholarly journals The Amino-Terminal Region of Vpr from Human Immunodeficiency Virus Type 1 Forms Ion Channels and Kills Neurons

1999 ◽  
Vol 73 (5) ◽  
pp. 4230-4238 ◽  
Author(s):  
S. C. Piller ◽  
G. D. Ewart ◽  
D. A. Jans ◽  
P. W. Gage ◽  
G. B. Cox
Keyword(s):  
Amino Acids ◽  
Human Immunodeficiency Virus ◽  
Cell Death ◽  
Ion Channels ◽  
Ion Channel ◽  
Lipid Bilayers ◽  
Planar Lipid Bilayers ◽  
Wild Type ◽  
Immunodeficiency Virus

ABSTRACT We have previously reported that the accessory protein Vpr from human immunodeficiency virus type 1 forms cation-selective ion channels in planar lipid bilayers and is able to depolarize intact cultured neurons by causing an inward sodium current, resulting in cell death. In this study, we used site-directed mutagenesis and synthetic peptides to identify the structural regions responsible for the above functions. Mutations in the N-terminal region of Vpr were found to affect channel activity, whereas this activity was not affected by mutations in the hydrophobic region of Vpr (amino acids 53 to 71). Analysis of mutants containing changes in the basic C terminus confirmed previous results that this region, although not necessary for ion channel function, was responsible for the observed rectification of wild-type Vpr currents. A peptide comprising the first 40 N-terminal amino acids of Vpr (N40) was found to be sufficient to form ion channels similar to those caused by wild-type Vpr in planar lipid bilayers. Furthermore, N40 was able to cause depolarization of the plasmalemma and cell death in cultured hippocampal neurons with a time course similar to that seen with wild-type Vpr, supporting the idea that this region is responsible for Vpr ion channel function and cytotoxic effects. Since Vpr is found in the serum and cerebrospinal fluids of AIDS patients, these results may have significance for AIDS pathology.

Generation of an agonistic binding site for blockers of the M3 muscarinic acetylcholine receptor

2008 ◽  
Vol 412 (1) ◽  
pp. 103-112 ◽  
Author(s):  
Doreen Thor ◽  
Angela Schulz ◽  
Thomas Hermsdorf ◽  
Torsten Schöneberg
Keyword(s):  
Ligand Binding ◽  
Binding Site ◽  
G Protein ◽  
Binding Sites ◽  
Expression System ◽  
Muscarinic Acetylcholine Receptor ◽  
Intracellular Loop ◽  
Inverse Agonists ◽  
Yeast Expression System ◽  
High Affinity

GPCRs (G-protein-coupled receptors) exist in a spontaneous equilibrium between active and inactive conformations that are stabilized by agonists and inverse agonists respectively. Because ligand binding of agonists and inverse agonists often occurs in a competitive manner, one can assume an overlap between both binding sites. Only a few studies report mutations in GPCRs that convert receptor blockers into agonists by unknown mechanisms. Taking advantage of a genetically modified yeast strain, we screened libraries of mutant M3Rs {M3 mAChRs [muscarinic ACh (acetylcholine) receptors)]} and identified 13 mutants which could be activated by atropine (EC50 0.3–10 μM), an inverse agonist on wild-type M3R. Many of the mutations sensitizing M3R to atropine activation were located at the junction of intracellular loop 3 and helix 6, a region known to be involved in G-protein coupling. In addition to atropine, the pharmacological switch was found for other M3R blockers such as scopolamine, pirenzepine and oxybutynine. However, atropine functions as an agonist on the mutant M3R only when expressed in yeast, but not in mammalian COS-7 cells, although high-affinity ligand binding was comparable in both expression systems. Interestingly, we found that atropine still blocks carbachol-induced activation of the M3R mutants in the yeast expression system by binding at the high-affinity-binding site (Ki ∼10 nM). Our results indicate that blocker-to-agonist converting mutations enable atropine to function as both agonist and antagonist by interaction with two functionally distinct binding sites.

Modulation of skeletal muscle Ca2(+)-release channel activity by sphingosine

1997 ◽  
Vol 272 (5) ◽  
pp. C1465-C1474 ◽  
Author(s):  
D. H. Needleman ◽  
B. Aghdasi ◽  
A. B. Seryshev ◽  
G. J. Schroepfer ◽  
S. L. Hamilton
Keyword(s):  
Skeletal Muscle ◽  
Lipid Bilayers ◽  
Binding Protein ◽  
Planar Lipid Bilayers ◽  
Dependent Manner ◽  
Carboxy Terminus ◽  
Release Channel ◽  
Proteolytic Fragment ◽  
High Affinity ◽  
High Affinity Site

The effect of D-erythro-C18-sphingosine (sphingosine) and related compounds on the Ca(2+)-release channel (ryanodine binding protein) was examined on rabbit skeletal muscle membranes, on the purified ryanodine binding protein, and on the channel reconstituted into planar lipid bilayers. Sphingosine inhibited [3H]ryanodine binding to sarcoplasmic reticulum (SR) membranes in a dose-dependent manner similar to published results (R. A. Sabbadini, R. Betto, A. Teresi, G. Fachechi-Cassano, and G. Salviati. J. Biol. Chem. 267: 15475-15484, 1992). The sphingolipid also inhibited [3H]ryanodine binding to the purified ryanodine binding protein. Our results demonstrate that the inhibition of [3H]ryanodine binding by sphingosine is due to an increased rate of dissociation of bound [3H]ryanodine from SR membranes and a decreased rate of association of [3H]ryanodine to the high-affinity site. Unlike other modulators of the Ca(2+)-release channel, sphingosine can remove bound [3H]ryanodine from the high-affinity site within minutes. Sphingosine increased the rate of dissociation of [3H]ryanodine bound to a solubilized proteolytic fragment derived from the carboxy terminus of the ryanodine binding protein (cleavage at Arg4475). Sphingosine also inhibited the activity of the Ca(2+)-release channel incorporated into planar lipid bilayers. Taken together, the data provide evidence for a direct effect of sphingosine on the Ca(2+)-release channel. Sphingosine is a noncompetitive inhibitor at the high-affinity ryanodine binding site, and it interacts with a site between Arg4475 and the carboxy terminus of the Ca(2+)-release channel.

scholarly journals Characterization of Human Immunodeficiency Virus Type 1 Monomeric and Trimeric gp120 Glycoproteins Stabilized in the CD4-Bound State: Antigenicity, Biophysics, and Immunogenicity

2007 ◽  
Vol 81 (11) ◽  
pp. 5579-5593 ◽  
Author(s):  
Barna Dey ◽  
Marie Pancera ◽  
Krisha Svehla ◽  
Yuuei Shu ◽  
Shi-Hua Xiang ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Binding Site ◽  
Human Immunodeficiency Virus Type ◽  
Envelope Glycoprotein ◽  
Neutralizing Antibodies ◽  
Bound State ◽  
Wild Type ◽  
Gp120 Envelope ◽  
Immunodeficiency Virus

ABSTRACT The human immunodeficiency virus type 1 exterior gp120 envelope glycoprotein is highly flexible, and this flexibility may contribute to the inability of monomeric gp120 immunogens to elicit broadly neutralizing antibodies. We previously showed that an S375W modification of a critical interfacial cavity central to the primary receptor binding site, the Phe43 cavity, stabilizes gp120 into the CD4-bound state. However, the immunological effects of this cavity-altering replacement were never tested. Subsequently, we screened other mutations that, along with the S375W alteration, might further stabilize the CD4-bound state. Here, we define a selected second cavity-altering replacement, T257S, and analyze the double mutations in several gp120 envelope glycoprotein contexts. The gp120 glycoproteins with the T257S-plus-S375W double mutation (T257S+S375W) have a superior antigenic profile compared to the originally identified single S375W replacement in terms of enhanced recognition by the broadly neutralizing CD4 binding-site antibody b12. Isothermal titration calorimetry measuring the entropy of the gp120 interaction with CD4 indicated that the double mutant was also stabilized into the CD4-bound state, with increasing relative fixation between core, full-length monomeric, and full-length trimeric versions of gp120. A significant increase in gp120 affinity for CD4 was also observed for the cavity-filling mutants relative to wild-type gp120. The most conformationally constrained T257S+S375W trimeric gp120 proteins were selected for immunogenicity analysis in rabbits and displayed a trend of improvement relative to their wild-type counterparts in terms of eliciting neutralizing antibodies. Together, the results suggest that conformational stabilization may improve the ability of gp120 to elicit neutralizing antibodies.

scholarly journals Location of the Permeation Pathway in the Recombinant Type 1 Inositol 1,4,5-Trisphosphate Receptor

1999 ◽  
Vol 114 (2) ◽  
pp. 243-250 ◽  
Author(s):  
Josefina Ramos-Franco ◽  
Daniel Galvan ◽  
Gregory A. Mignery ◽  
Michael Fill
Keyword(s):  
Lipid Bilayers ◽  
Mammalian Cells ◽  
Single Channel ◽  
Site Directed Mutagenesis ◽  
Recombinant Type ◽  
Mutation Strategy ◽  
Inositol 1,4,5 Trisphosphate ◽  
Trisphosphate Receptor ◽  
Permeation Properties

The inositol 1,4,5-trisphosphate receptor (InsP3R) forms ligand-regulated intracellular Ca2+ release channels in the endoplasmic reticulum of all mammalian cells. The InsP3R has been suggested to have six transmembrane regions (TMRs) near its carboxyl terminus. A TMR-deletion mutation strategy was applied to define the location of the InsP3R pore. Mutant InsP3Rs were expressed in COS-1 cells and single channel function was defined in planar lipid bilayers. Mutants having the fifth and sixth TMR (and the interceding lumenal loop), but missing all other TMRs, formed channels with permeation properties similar to wild-type channels (gCs = 284; gCa = 60 pS; PCa/PCs = 6.3). These mutant channels bound InsP3, but ligand occupancy did not regulate the constitutively open pore (Po > 0.80). We propose that a region of 191 amino acids (including the fifth and sixth TMR, residues 2398–2589) near the COOH terminus of the protein forms the InsP3R pore. Further, we have produced a constitutively open InsP3R pore mutant that is ideal for future site-directed mutagenesis studies of the structure–function relationships that define Ca2+ permeation through the InsP3R channel.

Characterization and mapping of the 12kDa FK506-binding protein (FKBP12)-binding site on different isoforms of the ryanodine receptor and of the inositol 1,4,5-trisphosphate receptor

2001 ◽  
Vol 354 (2) ◽  
pp. 413-422 ◽  
Author(s):  
Geert BULTYNCK ◽  
Patrick DE SMET ◽  
Daniela ROSSI ◽  
Geert CALLEWAERT ◽  
Ludwig MISSIAEN ◽  
...  
Keyword(s):  
Binding Site ◽  
Ryanodine Receptor ◽  
Binding Protein ◽  
Limited Proteolysis ◽  
Ip3 Receptor ◽  
Fk506 Binding Protein ◽  
High Affinity ◽  
Receptor Isoforms ◽  
Inositol 1,4,5 Trisphosphate ◽  
Affinity Interaction

We investigated the interaction of the 12kDa FK506-binding protein (FKBP12) with two ryanodine-receptor isoforms (RyR1 and RyR3) and with two myo-inositol 1,4,5-trisphosphate (IP3) receptor isoforms (IP3R1 and IP3R3). Using glutathione S-transferase (GST)-FKBP12 affinity chromatography, we could efficiently extract RyR1 (42±7% of the solubilized RyR1) from terminal cisternae of skeletal muscle as well as RyR3 (32±4% of the solubilized RyR3) from RyR3-overexpressing HEK-293 cells. These interactions were completely abolished by FK506 (20µM) but were largely unaffected by RyR-channel modulators. In contrast, neither IP3R1 nor IP3R3 from various sources, including rabbit cerebellum, A7r5 smooth-muscle cells and IP3R-overexpressing Sf9 insect cells from Spodoptera frugiperda, were retained on the GST-FKBP12 matrix. Moreover, immunoprecipitation experiments indicated a high-affinity interaction of FKBP12 with RyR1 but not with IP3R1. In order to determine the FKBP12-binding site, we fragmented both RyR1 and IP3R1 by limited proteolysis. We obtained a 45kDa fragment of RyR1 that bound to the GST-FKBP12 matrix, indicating that it retained all requirements for FKBP12 binding. This fragment was identified by its interaction with antibody m34C and must therefore contain its epitope (amino acids 2756–2803). However, no fragment of IP3R1 was retained on the column. These molecular data are in agreement with the lack of correlation between FKBP12 and IP3R1 expression in various cell types. The observation that FKBP12 did not affect IP3-induced Ca2+ release but reduced caffeine-induced Ca2+ release also indicated that mature IP3R1 and IP3R3, in contrast to RyR1 and RyR3, did not display a specific, high-affinity interaction with FKBP12.

scholarly journals Functional Consequences of Phosphomimetic Mutations at Key cAMP-dependent Protein Kinase Phosphorylation Sites in the Type 1 Inositol 1,4,5-Trisphosphate Receptor

2004 ◽  
Vol 279 (44) ◽  
pp. 46242-46252 ◽  
Author(s):  
Larry E. Wagner ◽  
Wen-Hong Li ◽  
Suresh K. Joseph ◽  
David I. Yule
Keyword(s):  
Splice Variants ◽  
Phosphorylation Sites ◽  
Wild Type ◽  
Igm Antibody ◽  
Temporal Properties ◽  
Inositol 1,4,5 Trisphosphate ◽  
Intracellular Ca ◽  
Spatio Temporal ◽  
In Cells

Regulation of Ca2+release through inositol 1,4,5-trisphosphate receptors (InsP3R) has important consequences for defining the particular spatio-temporal properties of intracellular Ca2+signals. In this study, regulation of Ca2+release by phosphorylation of type 1 InsP3R (InsP3R-1) was investigated by constructing “phosphomimetic” charge mutations in the functionally important phosphorylation sites of both the S2+ and S2- InsP3R-1 splice variants. Ca2+release was investigated following expression in Dt-40 3ko cells devoid of endogenous InsP3R. In cells expressing either the S1755E S2+ or S1589E/S1755E S2- InsP3R-1, InsP3-induced Ca2+release was markedly enhanced compared with nonphosphorylatable S2+ S1755A and S2- S1589A/S1755A mutants. Ca2+release through the S2- S1589E/S1755E InsP3R-1 was enhanced ∼8-fold over wild type and ∼50-fold when compared with the nonphosphorylatable S2- S1589A/S1755A mutant. In cells expressing S2- InsP3R-1 with single mutations in either S1589E or S1755E, the sensitivity of Ca2+release was enhanced ∼3-fold; sensitivity was midway between the wild type and the double glutamate mutation. Paradoxically, forskolin treatment of cells expressing either single Ser/Glu mutation failed to further enhance Ca2+release. The sensitivity of Ca2+release in cells expressing S2+ S1755E InsP3R-1 was comparable with the sensitivity of S2- S1589E/S1755E InsP3R-1. In contrast, mutation of S2+ S1589E InsP3R-1 resulted in a receptor with comparable sensitivity to wild type cells. Expression of S2- S1589E/S1755E InsP3R-1 resulted in robust Ca2+oscillations when cells were stimulated with concentrations of α-IgM antibody that were threshold for stimulation in S2- wild type InsP3R-1-expressing cells. However, at higher concentrations of α-IgM antibody, Ca2+oscillations of a similar period and magnitude were initiated in cells expressing either wild type or S2- phosphomimetic mutations. Thus, regulation by phosphorylation of the functional sensitivity of InsP3R-1 appears to define the threshold at which oscillations are initiated but not the frequency or amplitude of the signal when established.

scholarly journals Subcellular Localization of a High Affinity Binding Site ford-myo-Inositol 1,4,5-Trisphosphate fromChenopodium rubrum

2000 ◽  
Vol 124 (1) ◽  
pp. 475-483 ◽  
Author(s):  
Jan Martinec ◽  
Tomáš Feltl ◽  
Chris H. Scanlon ◽  
Peter J. Lumsden ◽  
Ivana Macháčková
Keyword(s):  
Subcellular Localization ◽  
Binding Site ◽  
Affinity Binding ◽  
High Affinity Binding ◽  
High Affinity ◽  
Inositol 1,4,5 Trisphosphate ◽  
High Affinity Binding Site

scholarly journals Single Channel Function of Inositol 1,4,5-trisphosphate Receptor Type-1 and -2 Isoform Domain-Swap Chimeras

2003 ◽  
Vol 121 (5) ◽  
pp. 399-411 ◽  
Author(s):  
Jorge Ramos ◽  
Wonyong Jung ◽  
Josefina Ramos-Franco ◽  
Gregory A. Mignery ◽  
Michael Fill
Keyword(s):  
Lipid Bilayers ◽  
Single Channel ◽  
Wild Type ◽  
Structural Determinants ◽  
Domain Swap ◽  
Channel Function ◽  
Recombinant Type ◽  
Ligand Regulation

The InsP3R proteins have three recognized domains, the InsP3-binding, regulatory/coupling, and channel domains (Mignery, G.A., and T.C. Südhof. 1990. EMBO J. 9:3893–3898). The InsP3 binding domain and the channel-forming domain are at opposite ends of the protein. Ligand regulation of the channel must involve communication between these different regions of the protein. This communication likely involves the interceding sequence (i.e., the regulatory/coupling domain). The single channel functional attributes of the full-length recombinant type-1, -2, and -3 InsP3R channels have been defined. Here, two type-1/type-2 InsP3R regulatory/coupling domain chimeras were created and their single channel function defined. One chimera (1-2-1) contained the type-2 regulatory/coupling domain in a type-1 backbone. The other chimera (2-1-2) contained the type-1 regulatory/coupling domain in a type-2 backbone. These chimeric proteins were expressed in COS cells, isolated, and then reconstituted in proteoliposomes. The proteoliposomes were incorporated into artificial planar lipid bilayers and the single-channel function of the chimeras defined. The chimeras had permeation properties like that of wild-type channels. The ligand regulatory properties of the chimeras were altered. The InsP3 and Ca2+ regulation had some unique features but also had features in common with wild-type channels. These results suggest that different independent structural determinants govern InsP3R permeation and ligand regulation. It also suggests that ligand regulation is a multideterminant process that involves several different regions of the protein. This study also demonstrates that a chimera approach can be applied to define InsP3R structure-function.

scholarly journals Novel Pol II Fusion Promoter Directs Human Immunodeficiency Virus Type 1-Inducible Coexpression of a Short Hairpin RNA and Protein

2006 ◽  
Vol 80 (4) ◽  
pp. 1863-1873 ◽  
Author(s):  
Hoshang J. Unwalla ◽  
Hai-Tang Li ◽  
Ingrid Bahner ◽  
Ming-Jie Li ◽  
Donald Kohn ◽  
...  
Keyword(s):  
Fluorescent Protein ◽  
Expression System ◽  
Short Hairpin Rna ◽  
Wild Type ◽  
Hairpin Rna ◽  
Pol Ii ◽  
Novel Approach ◽  
Short Hairpin ◽  
Hiv 1

ABSTRACT We demonstrate a novel approach for coexpression of a short hairpin RNA (shRNA) with an open reading frame which exploits transcriptional read-through of a minimal polyadenylation signal from a Pol II promoter. We first observed efficient inducible expression of enhanced green fluorescent protein along with an anti-rev shRNA. We took advantage of this observation to test coexpression of the transdominant negative mutant (humanized) of human immunodeficiency type 1 (HIV-1) Rev (huRevM10) along with an anti-rev shRNA via an HIV-1-inducible fusion promoter. The coexpression of the shRNA and transdominant protein resulted in potent, long-term inhibition of HIV-1 gene expression and suppression of shRNA-resistant mutants. This dual expression system has broad-based potential for other shRNA applications, such as cases where simultaneous knockdown of mutant and wild-type transcripts must be accompanied by replacement of the wild-type protein.

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