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To examine the molecular details of ligand activation of G-protein coupled receptors (GPCRs), emphasis has been placed on structure determination of these receptors with stabilizing ligands. Here we present the methodology for receptor dynamics characterization of the GPCR human [[beta].sub.2] adrenergic receptor bound to the inverse agonist carazolol using the technique of amide hydrogen/ deuterium exchange coupled with mass spectrometry (HDX MS). The HDX MS profile of receptor bound to carazolol is consistent with thermal parameter observations in the crystal structure and provides additional information in highly dynamic regions of the receptor and chemical modifications demonstrating the highly complementary nature of the techniques. After optimization of HDX experimental conditions for this membrane protein, better than 89% sequence coverage was obtained for the receptor. The methodology presented paves the way for future analysis of [[beta].sub.2]AR bound to pharmacologically distinct ligands as well as analysis of other GPCR family members. 10.1021/ac902484p

Plexin cell surface receptors bind to semaphorin ligands and transduce signals for regulating neuronal axon guidance. The intracellular region of plexins is essential for signaling and contains a R-Ras/M-Ras GTPase activating protein (GAP) domain that is divided into two segments by a Rho GTPase-binding domain (RBD). The regulation mechanisms for plexin remain elusive, although it is known that activation requires both binding of semaphorin to the extracellular region and a Rho-family GTPase (Rac1 or Rnd1) to the RBD. Here we report the crystal structure of the plexin A3 intracellular region. The structure shows that the N- and C-terminal portions of the GAP homologous regions together form a GAP domain with an overall fold similar to other Ras GAPs. However, the plexin GAP domain adopts a closed conformation and cannot accommodate R-Ras/M-Ras in its substrate-binding site, providing a structural basis for the autoinhibited state of plexins. A comparison with the plexin B1 RBD/Rnd1 complex structure suggests that Rnd1 binding alone does not induce a conformational change in plexin, explaining the requirement of both semaphorin and a Rho GTPase for activation. The structure also identifies an N-terminal segment that is important for regulation. Both the N-terminal segment and the RBD make extensive interactions with the GAP domain, suggesting the presence of an allosteric network connecting these three domains that integrates semaphorin and Rho GTPase signals to activate the GAP. The importance of these interactions in plexin signaling is shown by both cell-based and in vivo axon guidance assays. autoinhibition | axon guidance | signaling | structure

CCL19 and CCL21 are endogenous agonists for the seven-transmembrane receptor CCR7. They are equally active in promoting G protein stimulation and chemotaxis. Yet, we find that they result in striking differences in activation of the G protein-coupled receptor kinase (GRK)/[beta]-arrestin system. CCL19 leads to robust CCR7 phosphorylation and [beta]-arrestin2 recruitment catalyzed by both GRK3 and GRK6 whereas CCL21 activates GRK6 alone. This differential GRK activation leads to distinct functional consequences. Although each ligand leads to [beta]-arrestin2 recruitment, only CCL19 leads to redistribution of [beta]-arrestin2-GFP into endocytic vesicles and classical receptor desensitization. In contrast, these agonists are both capable of signaling through GRK6 and [beta]-arrestin2 to ERK kinases. Thus, this mechanism for 'ligand bias' whereby endogenous agonists activate different GRK isoforms leads to functionally distinct pools of [beta]-arrestin. CCR7 | CCL19 | CCL21 | chemokine | arrestin

Presynaptic glutamate release elicits brief waves of membrane depolarization in neurons by activating AMPA receptors. Depending on its precise size and shape, current through AMPA receptors gates downstream processes like NMDA receptor activation and action potential generation. Over a decade of research on AMPA receptor structure and function has identified binding sites on AMPA receptors for agonists, antagonists and allosteric modulators as well as key residues underlying differences in the gating behavior of various AMPA receptor subtypes. However, the recent discovery that AMPA receptors are accompanied in the synaptic membrane by a family of auxiliary subunits known as transmembrane AMPA receptor regulatory proteins (TARPs) has revealed that the kinetics and pharmacology of neuronal AMPA receptors differ in many respects from those predicted by classical studies of AMPA receptors in heterologous systems. Here, we summarize recent work and discuss remaining questions concerning the structure and function of native TARP-AMPA receptor complexes.

Mechanisms by which the extracellular domain of Notch1 controls Notch1 signaling are not well defined. Here, we show that the O-fucose glycan in the Notch1 ligand-binding domain regulates the strength of Notch1 signaling during embryogenesis, postweaning growth, and T cell development in the mouse. Heterozygotes carrying a Notch[1.sup.12f] allele and an inactive Notch1 allele die at approximately embryonic day (E)12 with a typical Notch1 null phenotype. Homozygous Notch[1.sup.12f/12f] mice are viable and fertile but grow somewhat more slowly than littermates after weaning. Notch[1.sup.12f/12f] thymocytes bind less Delta1 and exhibit reduced Notch1 signaling. The number of double-positive (DP) and singlepositive (SP) T cells are decreased in Notch[1.sup.12f/12f] thymus, and DP T cells are more apoptotic. By contrast, proportionately more SP cells have matured, and SP-to-DP ratios are increased in mutant thymus. Thus, the O-fucose glycan in EGF12 of mouse Notch1 is required for optimal Notch1 signaling and T cell development in mammals. hypomorphic mutation | Notch signaling | O-fucosylation mutant

A capillary electrophoresis (CE) laser-induced fluorescence (LIF) assay was developed for the detection of G protein coupled receptor mediated adenylyl cyclase (AC) activity using BODIPY FL ATP (BATP) as substrate. In the assay, cell membranes coexpressing the stimulatory G protein fused to the [[beta].sub.2] adrenergic receptor ([[beta].sub.2]AR) and AC were incubated with BATP, the resultant mixture injected, and BATP separated from product BODIPY FL cAMP (BcAMP) by CE. AC activity was quantified by measuring the rate of BcAMP formation, [[beta].sub.2]AR agonists isoproterenol and terbutaline increased basal AC activity with [EC.sub.50]s of 2.4 [+ or -] 0.2 and 60 [+ or -] 9 nM, respectively. The antagonist propranolol competed with terbutaline for [[beta].sub.2]AR binding sites and expectedly right-shifted the terbutaline dose-response curve to 8 [+ or -] 3 [micro]M. The high sensitivity of the assay was demonstrated by detection of small changes in AC activity, with the partial agonist alprenolol increasing (22 [+ or -] 1%) and the inverse agonist ICI 118,551 decreasing (19 [+ or -] 2%) basal activity. The simplicity and automation of the CE-LIF assay offers advantages over the more traditional assay using radiochemical ATP and column chromatography.

Anatomical visualization of neurotransmitter receptor localization is facilitated by tagging receptors, but this process can alter their functional properties. We have evaluated the distribution and properties of WT glutamate receptor 3 (GluR3) [alpha]-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (WT GluR3) and two receptors in which GFP was tagged to the amino terminus (GFP-GluR3) or to the carboxyl terminus (GluR3-GFP). Although the fluorescence in Xenopus oocytes was stronger in the vegetal hemisphere because of localization of internal structures (probable sites of production, storage or recycling of receptors), the insertion of receptors into the plasma membrane was polarized to the animal hemisphere. The fluorescence intensity of oocytes injected with GluR3-GFP RNA was approximately double that of oocytes injected with GFP-GluR3 RNA. Accordingly, GluR3-GFP oocytes generated larger kainate-induced currents than GFP-GluR3 oo-cytes, with similar [EC.sub.50] values. Currents elicited by glutamate, or AMPA coapplied with cyclothiazide, were also larger in GluR3-GFP oocytes. The glutamate- to kainate-current amplitude ratios differed, with GluR3-GFP being activated more efficiently by glutamate than the WT or GFP-GluR3 receptors. This pattern correlates with the slower decay of glutamate-induced currents generated by GluR3-GFP receptors. These changes were not observed when GFP was tagged to the amino terminus, and these receptors behaved like the WT. The antagonistic effects of 6-nitro-7-sulfamoylbenzo[f]quinoxaline-2,3-dione (NBQX) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were not altered in any of the tagged receptors. We conclude that GFP is a useful and convenient tag for visualizing these proteins. However, the effects of different sites of tag insertion on receptor characteristics must be taken into account in assessing the roles played by these receptor proteins. fluorescent tag | receptor expression | Xenopus oocytes | kainate | glutamate

The orphan glutamate-like receptor GluR[delta]2 is predominantly expressed in Purkinje cells of the central nervous system. The classification of GluR[delta]2 to the ionotropic glutamate receptor family is based on sequence similarities, because GluR[delta]2 does not form functional homomeric glutamate-gated ion channels in transfected cells. Studies in GluR[delta][2.sup.-/-] knockout mice as well as in mice with naturally occurring mutations in the GluR[delta]2 gene have demonstrated an essential role of GluR[delta]2 in cerebellar long-term depression, motor learning, motor coordination, and synaptogenesis. However, the lack of a known agonist has hampered investigations on the function of GluR[delta]2. In this study, the ligand-binding core of GluR[delta]2 (GluR[delta]2-S1S2) was found to bind neutral amino acids such as D-serine and glycine, as demonstrated by isothermal titration calorimetry. Direct evidence for binding of D-serine and structural rearrangements in the binding cleft of GluR[delta]2-SIS2 is provided by x-ray structures of GluR[delta]2-SIS2 in its apo form and in complex with D-serine. Functionally, D-serine and glycine were shown to inactivate spontaneous ion-channel conductance in GluR[delta]2 containing the lurcher mutation (E[C.sub.50] values, 182 and [micro]M, respectively). These data demonstrate that the GluR[delta]2 ligand-binding core is capable of binding ligands and that cleft closure of the ligand-binding core can induce conformational changes that alter ion permeation. crystal structure | electrophysiology | isothermal titration calorimetry | ligand-binding core

Viral and synthetic single-stranded RNAs are the ligands for Toll-like receptor (TLR)7 and TLR8. However, single-stranded RNA is rapidly degraded by ubiquitous RNases, and the studies reported to date have used RNA with lipid carriers. To overcome nuclease susceptibility of RNA, we have synthesized several RNAs incorporating a range of chemical modifications. The present study describes one pool of RNA compounds, referred to as stabilized immune modulatory RNA (SIMRA) compounds, in which two RNA segments are attached through their 3' ends. SIMRA compounds showed greater stability in human serum compared with linear RNA and activated human TLR8, but not TLR7, in HEK293 cells without using lipid carriers. Interestingly, another set of SIMRA compounds containing 7-deazaguanosine substituted for natural guanosine activated human TLR7 and TLR8. Additionally, TLR7- and TLR8-activating compounds, but not the compounds that activated only TLR8, stimulated mouse immune cells in vitro and in vivo and produced dose-dependent T helper 1-type cytokines. Both types of compounds activated human peripheral blood mononuclear cells, but only TLR7- and TLR8-activating compounds activated plasmacytoid dendritic cells and produced high levels of IFN-[alpha]. In monkeys, s.c. administration of both types of SIMRA compounds induced transient changes in peripheral blood monocytes and neutrophils, and activated T lymphocytes, monocytes, and NK cells. Both types of compounds induced IFN-[gamma]-inducible protein 10, but only the 7-deazaguanosine-containing compound that activated both TLR7 and TLR8 induced IFN-[alpha] in monkeys. This is a comprehensive study of RNA-based compounds containing structures and synthetic stimulatory motifs in mouse, monkey, and human systems without using lipid carriers. oligoribonucleotides

The TrkC/NT-3 receptor/ligand pair is believed to be part of the classic neurotrophic theory claiming that neuronal death occurs by default when neurotrophic factors become limited, through loss of survival signals. Here, we show that TrkC is a dependence receptor and, as such, induces caspase-dependent apoptotic death in the absence of NT-3 in immortalized cells, a proapoptotic activity inhibited by the presence of NT-3. This proapoptotic activity of TrkC relies on the caspase-mediated cleavage of the intracellular domain of TrkC, which permits the release of a proapoptotic fragment. This fragment induces apoptosis through a caspase-9-dependent mechanism. Finally, we show that the death of dorsal root ganglion (DRG) neurons provoked by NT-3 withdrawal is inhibited when TrkC-proapoptotic activity is antagonized. Thus, the death of neurons upon disappearance of NT-3 is not only due to a loss of survival signals but also to the active proapoptotic activity of the unbound TrkC dependence receptor. neurotrophin-3 | sensory neurons | programmed cell death | tyrosine kinase

Seven-transmembrane receptors are prototypic allosteric proteins with the ability to adopt numerous conformations, many of which interact with cellular partners to initiate cellular biochemical processes. Defining efficacy as the ability of ligands to stabilize some of these conformations (which, in turn, possess physiological activity) presents a wider definition of efficacy beyond simple integrated cellular response; numerous or 'pluridimensional' efficacies are required to describe ligands. Specifically, some agonists might only partially activate the library of potential signaling systems in a cell or some antagonists might actively induce receptor internalization without activation. This article reviews data to demonstrate that there is no longer support for a linear view of efficacy whereby a single receptor activation state triggers all possible receptor interactions with a cell. Instead, a view of collateral efficacy, in which ligands can produce portions of the possible behaviors of receptors, is presented. Concepts related to the molecular mechanism for this effect (discussed in the literature as 'stimulus trafficking', 'biased agonism' or 'functional selectivity') and discussion of the possible therapeutic implications of this mechanism are presented.

Seven-transmembrane receptors (7TMRs), the most common molecular targets of modern drug therapy, are critically regulated by [beta]-arrestins, which both inhibit classic G-protein signaling and initiate distinct [beta]-arrestin signaling. The interplay of G-protein and [beta]-arrestin signals largely determines the cellular consequences of 7TMR-targeted drugs. Until recently, a drug's efficacy for [beta]-arrestin recruitment was believed to be proportional to its efficacy for G-protein activities. This paradigm restricts 7TMR drug effects to a linear spectrum of responses, ranging from inhibition of all responses to stimulation of all responses. However, it is now clear that 'biased ligands' can selectively activate G-protein or [beta]-arrestin functions and thus elicit novel biological effects from even well-studied 7TMRs. Here, we discuss the current state of [beta]-arrestin-biased ligand research and the prospects for [beta]-arrestin bias as a therapeutic target. Consideration of ligand bias might have profound influences on the way scientists approach 7TMR-targeted drug discovery.

Antagonist affinity measurements have traditionally been considered important in characterizing the cell-surface receptors present in a particular cell or tissue. A central assumption has been that antagonist affinity is constant for a given receptor-antagonist interaction, regardless of the agonist used to stimulate that receptor or the downstream response that is measured. As a consequence, changes in antagonist affinity values have been taken as initial evidence for the presence of novel receptor subtypes. Emerging evidence suggests, however, that receptors can possess multiple binding sites and the same receptor can show different antagonist affinity measurements under distinct experimental conditions. Here, we discuss several mechanisms by which antagonists have different affinities for the same receptor as a consequence of allosterism, coupling to different G proteins, multiple (but non-interacting) receptor sites, and signal-pathway-dependent pharmacology (where the pharmacology observed varies depending on the signalling pathway measured).

Members of the Bcl-2 family of proteins regulate apoptosis, with some of their physiological effects mediated by their modulation of endoplasmic reticulum (ER) [Ca.sup.2+] homeostasis. Antiapoptotic Bcl-[x.sub.L] binds to the inositol trisphosphate receptor (Ins[P.sub.3]R) [Ca.sup.2+] release channel to enhance [Ca.sup.2+]- and Ins[P.sub.3]-dependent regulation of channel gating, resulting in reduced ER [[Ca.sup.2+]], increased oscillations of cytoplasmic [Ca.sup.2+] concentration ([[[Ca.sup.2+]].sub.i]), and apoptosis resistance. However, it is controversial which Ins[P.sub.3]R isoforms mediate these effects and whether reduced ER [[Ca.sup.2+]] or enhanced [[[Ca.sup.2+]].sub.i] signaling is most relevant for apoptosis protection. DT40 cell lines engineered to express each of the three mammalian Ins[P.sub.3]R isoforms individually displayed enhanced apoptosis sensitivity compared with cells lacking [InsP.sub.3]R. In contrast, coexpression of each isoform with Bcl-[x.sub.L] conferred enhanced apoptosis resistance. In single-channel recordings of channel gating in native ER membranes, Bcl-[x.sub.L] increased the apparent sensitivity of all three Ins[P.sub.3]R isoforms to subsaturating levels of Ins[P.sub.3]. Expression of Bcl-[x.sub.L] reduced ER [[Ca.sup.2+]] in type 3 but not type 1 or 2 Ins[P.sub.3]R-expressing cells. In contrast, Bcl-[x.sub.L] enhanced spontaneous [[[Ca.sup.2+]].sub.i] signaling in all three Ins[P.sub.3]R isoform-expressing cell lines. These results demonstrate a redundancy among Ins[P.sub.3]R isoforms in their ability to sensitize cells to apoptotic insults and to interact with Bcl-[x.sub.L] to modulate their activities that result in enhanced apoptosis resistance. Furthermore, these data suggest that modulation of ER [[Ca.sup.2+]] is not a specific requirement for ER-dependent antiapoptotic effects of Bd-[x.sub.L]. Rather, apoptosis protection is conferred by enhanced spontaneous [[[Ca.sup.2+]].sub.i] signaling by Bcl-[x.sub.L] interaction with all isoforms of the Ins[P.sub.3]R. Bcl-2 | calcium | endoplasmic reticulum | B-cells

In pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI), plant cell surface receptors sense potential microbial pathogens by recognizing elicitors called PAMPs. Although diverse PAMPs trigger PTI through distinct receptors, the resulting intracellular responses overlap extensively. Despite this, a common component(s) linking signal perception with transduction remains unknown. In this study, we identify SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK)3/brassinosteroid-associated kinase (BAK)1, a receptor-like kinase previously implicated in hormone signaling, as a component of plant PTI. In Arabidopsis thaliana, AtSERK3/BAK1 rapidly enters an elicitor-dependent complex with FLAGELLIN SENSING 2 (FLS2), the receptor for the bacterial PAMP flagellin and its peptide derivative flg22. In the absence of AtSERK3/BAK1, early flg22-dependent responses are greatly reduced in both A. thaliana and Nicotiana benthamiana. Furthermore, N. benthamiana Serk3/Bak1 is required for full responses to unrelated PAMPs and, importantly, for restriction of bacterial and oomycete infections. Thus, SERK3/BAK1 appears to integrate diverse perception events into downstream PAMP responses, leading to immunity against a range of invading microbes. flg22 | Arabidopsis | nicotiana | Flagellin | brassinosteroid

The highly polymorphic S-locus receptor kinase (SRK) is the stigma determinant of specificity in the self-incompatibility response of the Brassicaceae. SRK spans the plasma membrane of stigma epidermal cells, and it is activated in an allele-specific manner on binding of its extracellular region (eSRK) to its cognate pollen coat-localized S-locus cysteine-rich (SCR) ligand. SRK, like several other receptor kinases, forms dimers in the absence of ligand. To identify domains in SRK that mediate ligand-independent dimerization, we assayed eSRK for self-interaction in yeast. We show that SRK dimerization is mediated by two regions in eSRK, primarily by a C-terminal region inferred by homology modeling/fold recognition techniques to assume a PAN_APPLE-like structure, and secondarily by a region containing a signature sequence of the S-domain gene family, which might assume an EGF-like structure. We also show that eSRK exhibits a marked preference for homodimerization over heterodimerization with other eSRK variants and that this preference is mediated by a small, highly variable region within the PAN_APPLE domain. Thus, the extensive polymorphism exhibited by the eSRK not only determines differential affinity toward the SCR ligand, as has been assumed thus far, but also underlies a previously unrecognized allelic specificity in SRK dimerization. We propose that preference for SRK homodimerization explains the codominance exhibited by a majority of SRKs in the typically heterozygous stigmas of self-incompatible plants, whereas an increased propensity for heterodimerization combined with reduced affinity of heterodimers for cognate SCRs might underlie the dominant-recessive or mutual weakening relationships exhibited by some SRK allelic pairs. self-incompatibility | ligand-independent receptor dimerization | yeast two-hybrid

G protein-coupled receptors (GPCRs) have been found as monomers but also as dimers or higher-order oligomers in cells. The relevance of the monomeric or dimeric receptor state for G protein activation is currently under debate for class A rhodopsin-like GPCRs. Clarification of this issue requires the availability of well defined receptor preparations as monomers or dimers and an assessment of their ligand-binding and G protein-coupling properties. We show by pharmacological and hydrodynamic experiments that purified neurotensin receptor NTS1, a class A GPCR, dimerizes in detergent solution in a concentration-dependent manner, with an apparent affinity in the low nanomolar range. At low receptor concentrations, NTS1 binds the agonist neurotensin with a Hill slope of [approximately equal to]1; at higher receptor concentrations, neurotensin binding displays positive cooperativity with a Hill slope of [approximately equal to]2. NTS1 monomers activate G[alpha]q[[beta].sub.1][[gamma].sub.2], whereas receptor dimers catalyze nucleotide exchange with lower affinity. Our results demonstrate that NTS1 dimerization per se is not a prerequisite for G protein activation. dimer | G protein activation | G protein-coupled receptor | monomer

Presynaptic ionotropic glutamate receptors are emerging as key players in the regulation of synaptic transmission. Here we identify GluR7, a kainate receptor (KAR) subunit with no known function in the brain, as an essential subunit of presynaptic autoreceptors that facilitate hippocampal mossy fiber synaptic transmission. [GluR7.sup.-/-] mice display markedly reduced short- and long-term synaptic potentiation. Our data suggest that presynaptic KARs are GluR6/ GluR7 heteromers that coassemble and are localized within synapses. We show that recombinant GluR6/GluR7 KARs exhibit low sensitivity to glutamate, and we provide evidence that presynaptic KARs at mossy fiber synapses are likely activated by high concentrations of glutamate, Overall, from our data, we propose a model whereby presynaptic KARs are localized in the presynaptic active zone close to release sites, display low affinity for glutamate, are likely [Ca.sup.2+]-permeable, are activated by single release events, and operate within a short time window to facilitate the subsequent release of glutamate. kainate receptors | presynaptic glutamate receptors | short-term plasticity | synaptic plasticity

CD6 is a lymphocyte receptor that belongs to the scavenger receptor cysteine-rich superfamily. Because some members of the scavenger receptor cysteine-rich superfamily act as pattern recognition receptors for microbial components, we studied whether CD6 shares this function. We produced a recombinant form of the ectodomain of CD6 (rsCD6), which was indistinguishable (in apparent molecular mass, antibody reactivity, and cell binding properties) from a circulating form of CD6 affinity-purified from human serum, rsCD6 bound to and aggregated several Gram-positive and -negative bacterial strains through the recognition of lipoteichoic acid and LPS, respectively. The [K.sub.d] of the LPS--rsCD6 interaction was 2.69 [+ or -] 0.32 x [10.sup.-8] M, which is similar to that reported for the LPS-CD14 interaction. Further experiments showed that membrane CD6 also retains the LPS-binding ability, and it results in activation of the MAPK signaling cascade. In vivo experiments demonstrated that i.p. administration of rsCD6 before lethal LPS challenge significantly improved mice survival, and this was concomitant with reduced serum levels of the proinflammatory cytokines TNF-[alpha], IL6, and IL-1[beta]. in conclusion, our results illustrate the unprecedented bacterial binding properties of rsCD6 and support its therapeutic potential for the intervention of septic shock syndrome or other inflammatory diseases of infectious origin. bacterial cell component | innate immunity | lymphocyte surface receptor

Neuropeptide signaling requires the presence of G protein-coupled receptors (GPCRs) at the cell surface. Activated GPCRs interact with [beta]-arrestins, which mediate receptor desensitization, endocytosis, and mitogenic signaling, and the peptide-receptor-arrestin complex is sequestered into endosomes. Although dissociation of [beta]-arrestins is required for receptor recycling and resensitization, the critical event that initiates this process is unknown. Here we report that the agonist availability in the endosomes, controlled by the membrane metalloendopeptidase endothelin-converting enzyme 1 (ECE-1), determines stability of the peptide-receptor-arrestin complex and regulates receptor recycling and resensitization. Substance P (SP) binding to the tachykinin neurokinin 1 receptor ([NK.sub.1]R) induced membrane translocation of [beta]-arrestins followed by trafficking of the SP-[NK.sub.1] R-[beta]-arrestin complex to early endosomes containing ECE-1a-d. ECE-1 degraded SP in acidified endosomes, disrupting the complex; [beta]-arrestins returned to the cytosol, and the [NK.sub.1]R, freed from [beta]-arrestins, recycled and resensitized. An ECE-1 inhibitor, by preventing [NK.sub.1]R recycling in endothelial cells, inhibited resensitization of SP-induced inflammation. This mechanism is a general one because ECE-1 similarly regulated [NK.sub.3]R resensitization. Thus, peptide availability in endosomes, here regulated by ECE-1, determines the stability of the peptidereceptor-arrestin complex. This mechanism regulates receptor recycling, which is necessary for sustained signaling, and it may also control [beta]-arrestin-dependent mitogenic signaling of endocytosed receptors. We propose that other endosomal enzymes and transporters may similarly control the availability of transmitters in endosomes to regulate trafficking and signaling of GPCRs. Antagonism of these endosomal processes represents a strategy for inhibiting sustained signaling of receptors, and defects may explain the tachyphylaxis of drugs that are receptor agonists. G protein-coupled receptor trafficking| peptidase | resensitization | substance P | inflammation

High level bacterial expression systems and purification protocols are generated for the extracellular region of receptor for advanced glycation end products (RAGE) to enable biophysical and structural characterization of its tertiary and quaternary structure. The results presents the V and C1 domains are not independent domains but forms an integrated structural unit.

Learning and memory depend on persistent changes in synaptic strength that require neuronal gene expression. An unresolved question concerns the mechanisms by which activity at synapses is transduced into a nuclear transcriptional response. In the prevailing view, N-methyl-o-aspartate (NMDA)- and [alpha]-amino-3-hydroxy5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors have distinct roles in controlling synaptic strength: AMPA receptors effect short-term changes in synaptic strength, whereas NMDA receptors regulate genes that are required for the long-term maintenance of these changes. Here, we review recent data on the roles of these two types of receptor in activity-dependent gene expression. We discuss evidence that signals from NMDA receptors and AMPA receptors are integrated to specify transcriptional responses for particular plasticity related genes.

The structure and dynamics of PDZ of cystic fibrosis transmembrane regulator (CFTR)-associated ligand (CAL) and the complex formed with CFTR employing high-resolution NMR is characterized. It suggested that sites are targeted in the development of PDZ-selective inhibitors that help modulate CFTR function when the side chains make a number of contacts with the PDZ domain and interactions differ from those in the CTFR-EBP50 complex.

The study suggests that annexins play an important role in the endocrytic pathway that involves in the generation localization or fusion of endocrytic compartments. The conclusion states that annexins can play a role of transmembrane receptors when attached to membranes in the calcium presence and can function to initiate calcium-regulated coated pit formation at the cell surface or the intracellular organelles.

The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a cAMP-regulated epithelial [Cl.sup.-] channel that, when defective, causes cystic fibrosis. Screening of a collection of 100,000 diverse small molecules revealed tour novel chemical classes of CFTR inhibitors with [K.sub.i] 10 [micro]M, one of which (glycine hydrazides) had many active structural analogues. Analysis of a series of synthesized glycine hydrazide analogues revealed maximal inhibitory potency for N-(2-naphthalenyl) and 3,5-dibromo-2,4-dihydroxyphenyl substituents. The compound N-(2-naphthalenyl)-[(3,5-dibromo-2,4-dihydroxyphenyl)methylene] glycine hydrazide (GlyH-101) reversibly inhibited CFTR [C1.sup.-] conductance in KEY WORDS: cystic fibrosis * diarrhea * high-throughput screening * patch-clamp * drug discovery