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Extracellular N-terminal Domain (extracellular + n-terminal_domain)
Selected AbstractsReview article: proteinase-activated receptors , novel signals for gastrointestinal pathophysiologyALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 3 2000Vergnolle Proteinase-activated receptors (PARs) have the common property of being activated by the proteolytic cleavage of their extracellular N-terminal domain. The new NH2 -terminus acts as a ,tethered ligand' binding and activating the receptor itself. Four members of this family have been cloned, three of which are activated by thrombin (PAR-1, PAR-3 and PAR-4) while the fourth (PAR-2) is activated by trypsin or mast cell tryptase. In physiological or pathophysiological conditions, the gastrointestinal tract is exposed more than other tissues to proteinases (digestive enzymes, proteinases from pathogens or proteinases from inflammatory cells) that can activate PARs. Since PARs are highly expressed throughout the gastrointestinal tract, the study of the role of PARs in these tissues appears to be particularly important. It has already been shown that PAR-2 activation induces calcium mobilization and eicosanoid production in enterocytes as well as changes in ion transport in jejunal tissue segments. PAR-2 activation also causes calcium mobilization and stimulates amylase release from pancreatic acini. Moreover, both PAR-1 and PAR-2 activation can alter the gastrointestinal motility. In inflammatory or allergic conditions, the proteinases that constitute the major agonists for PARs (thrombin, trypsin and mast cell tryptase) are usually released. The activation of PARs by these proteinases might contribute to the gastrointestinal disorders associated with these pathologies. A complete understanding of the role of PARs in the gastrointestinal tract will require the development of selective receptor antagonists that are not yet available. Nonetheless, the use of PAR agonists has already highlighted new potential functions for proteinases in the gastrointestinal tract, thus the control of PAR activation might represent a promising therapeutic target. [source] Protease-activated receptor-4 (PAR4): a role as inhibitor of visceral pain and hypersensitivityNEUROGASTROENTEROLOGY & MOTILITY, Issue 11 2009C. Augé Abstract, Protease-activated receptor-4 (PAR4) belongs to the family of receptors activated by the proteolytic cleavage of their extracellular N-terminal domain and the subsequent binding of the newly released N-terminus. While largely expressed in the colon, the role of PAR4 in gut functions has not been defined. We have investigated the effects of PAR4 agonist on colonic sensations and sensory neuron signalling, and its role in visceral pain. We observed that a single administration of the PAR4 agonist peptide (AYPGKF-NH2), but not the control peptide (YAPGKF-NH2) into the colon lumen of mice significantly reduced the visceromotor response to colorectal distension at different pressures of distension. Further, intracolonic administration of the PAR4 agonist, but not the control peptide, was able to significantly inhibit PAR2 agonist- and transcient receptor potential vanilloid-4 (TRPV4) agonist-induced allodynia and hyperalgesia in response to colorectal distension. Protease-activated receptor-4 was detected in sensory neurons projecting from the colon, and isolated from the dorsal root ganglia, where it co-expressed with PAR2 and TRPV4. In total sensory neurons, PAR4 agonist exposure inhibited free intracellular calcium mobilization induced by the pro-nociceptive agonists of PAR2 and TRPV4. Finally, PAR4 -deficient mice experienced increased pain behaviour in response to intracolonic administration of mustard oil, compared with wild-type littermates. These results show that PAR4 agonists modulate colonic nociceptive response, inhibit colonic hypersensitivity and primary afferent responses to pro-nociceptive mediators. Endogenous activation of PAR4 also plays a major role in controlling visceral pain. These results identify PAR4 as a previously unknown modulator of visceral nociception. [source] The ,1 and ,6 subunit subtypes of the mammalian GABAA receptor confer distinct channel gating kineticsTHE JOURNAL OF PHYSIOLOGY, Issue 2 2004Janet L. Fisher The GABAA receptors show a large degree of structural heterogeneity, with seven different subunit families, and 16 different subtypes in mammalian species. The , family is the largest, with six different subtypes. The ,1 and ,6 subtypes are among the most diverse within this family and confer distinct pharmacological properties to recombinant and neuronal receptors. To determine whether different single channel and macroscopic kinetic properties were also associated with these subtypes, the ,1 or ,6 subunit was expressed in mammalian cells along with ,3 and ,2L subunits and the kinetic properties examined with outside-out patch recordings. The ,1,3,2L receptors responded to GABA with long-duration openings organized into multi-opening bursts. In contrast, channel openings of the ,6,3,2L receptors were predominately short in duration and occurred as isolated, single openings. The subunit subtype also affected the deactivation rate of the receptor, which was almost 2-fold slower for ,6,3,2L, compared with the ,1,3,2L isoform. Onset of fast desensitization did not differ between the isoforms. To determine the structural domains responsible for these differences in kinetic properties, we constructed six chimeric subunits, combining different regions of the ,1 and ,6 subunits. The properties of the chimeric subunits indicated that structures within the third transmembrane domain (TM3) and the TM3,TM4 intracellular loop conferred differences in single channel gating kinetics that subsequently affected the deactivation rate and GABA EC50. The effect of agonist concentration on the rise time of the current showed that the extracellular N-terminal domain was largely responsible for binding characteristics, while the transmembrane domains determined the activation rate at saturating GABA concentrations. This suggests that subunit structures outside of the agonist binding and pore-lining domains are responsible for the kinetic differences conferred by the ,1 and ,6 subtypes. Structural heterogeneity within these transmembrane and intracellular regions can therefore influence the characteristics of the postsynaptic response of GABAA receptors with different subunit composition. [source] Receptors for calcitonin gene-related peptide and adrenomedullin: implications for skin cell biologyEXPERIMENTAL DERMATOLOGY, Issue 9 2004J. A. Fischer The specificity of a G-protein-coupled calcitonin receptor (CTR) and a CT receptor-like receptor (CLR) for calcitonin gene-related peptide (CGRP), adrenomedullin (AM) and amylin is defined by the heterodimeric non-covalent association with three receptor-activity-modifying proteins (RAMPs). Chemical cross-linking of proteins at the cell surface and immunoprecipitation have identified [125I]CGRP/CLR/RAMP1, [125I]AM/CLR/RAMP2 and -3 as well as [125I]CGRP/CTR/RAMP1, [125I]amylin/CTR/RAMP1 and -RAMP3 complexes. CLR/RAMP1 defines a CGRP receptor. CLR/RAMP2 and -3 correspond to AM1 and AM2 receptor isotypes, respectively. The AM1 receptor cross-reacts with CGRP at high and the AM2 receptor at low concentrations. With the N-terminal deletion of amino acids 14,20 of the mouse, CLR-selective inactivation of AM over CGRP receptor function was obtained. As a result, functional interaction with AM was no longer possible. Overexpression of the CLR in transgenic mice together with the endogenous RAMP2 results in thinning of the hairs during postnatal development (L. M. Ittner et al. conference poster). In conclusion, the extreme N-terminus of the CLR and the extracellular N-terminal domains of RAMP1 and -2 contain amino acid residues that provide AM- or CGRP-binding selectivity of the CLR/RAMP complexes. Hair development is attenuated, resulting in the thinning of the hairs and eventually alopecia during postnatal development. [source] Synthesis of Novel Peptide Inhibitors of Thrombin-induced Platelet ActivationCHEMICAL BIOLOGY & DRUG DESIGN, Issue 5 2006Fernanda M. Burke Inhibitors of the activation of platelet aggregation have promise as important therapeutic agents for the management of acute coronary syndrome (ACS). Platelet activation by thrombin, a serine protease, occurs by binding to and cleavage of the extracellular N-terminal domains of protease-activated receptors 1 and 4 (PAR1 and PAR4). The proteolysis of the PARs exposes new tethered ligands that then signal through transmembrane domains to initiate platelet activation as a downstream effect. A pentapeptide cleavage product of bradykinin with the sequence Arg-Pro-Pro-Gly-Phe serves as a thrombin inhibitor by blocking , - and , -thrombin-induced platelet aggregation. Analogs of RPPGF have been prepared that result in improved inhibition of thrombin activation of platelets. Specific amino acid residues required for activity against platelet aggregation have been identified, and a lead compound, rOicPaPhe(p -Me)-NH2 (FM19), has been developed. FM19, which completely inhibits threshold , -thrombin-induced platelet aggregation at a concentration of 16 ± 4 ,m, represents an important lead compound in the development of inhibitors of thrombin-mediated platelet aggregation for treatment of ACS. [source] | |||||||||||||