35 research outputs found
The design and construction of floating- element skin-friction balances for use at 50 deg to 150 deg F
Design and construction of floating element skin friction balance
Chemotype-selective Modes of Action of Îș-Opioid Receptor Agonists
The crystal structures of opioid receptors provide a novel platform for inquiry into opioid receptor function. The molecular determinants for activation of the Îș-opioid receptor (KOR) were studied using a combination of agonist docking, functional assays, and site-directed mutagenesis. Eighteen positions in the putative agonist binding site of KOR were selected and evaluated for their effects on receptor binding and activation by ligands representing four distinct chemotypes: the peptide dynorphin A(1â17), the arylacetamide U-69593, and the non-charged ligands salvinorin A and the octahydroisoquinolinone carboxamide 1xx. Minimally biased docking of the tested ligands into the antagonist-bound KOR structure generated distinct binding modes, which were then evaluated biochemically and pharmacologically. Our analysis identified two types of mutations: those that affect receptor function primarily via ligand binding and those that primarily affect function. The shared and differential mechanisms of agonist binding and activation in KOR are further discussed. Usually, mutations affecting function more than binding were located at the periphery of the binding site and did not interact strongly with the various ligands. Analysis of the crystal structure along with the present results provide fundamental insights into the activation mechanism of the KOR and suggest that âfunctionalâ residues, along with water molecules detected in the crystal structure, may be directly involved in transduction of the agonist binding event into structural changes at the conserved rotamer switches, thus leading to receptor activation
Single Amino Acid Variation Underlies Species-Specific Sensitivity to Amphibian Skin-Derived Opioid-like Peptides
It has been suggested that the evolution of vertebrate opioid receptors (ORs) follow a vector of increased functionality. Here we test this idea comparing human and frog ORs. Interestingly, some of the most potent opioid peptides known have been isolated from amphibian skin secretions. Here we show that such peptides (dermorphin and deltorphin) are highly potent in the human receptors and inactive in frog ORs. The molecular basis for the insensitivity of the frog ORs to these peptides was studied using chimeras and molecular modeling. Interestingly, the insensitivity of the delta opioid receptor (DOR) to deltorphin was due to variation of a single amino acidâ Trp7.35âwhich is a leucine in mammalian DORs. Notably, Trp7.35 is completely conserved in all known DOR sequences from lamprey, fish and amphibians. The deltorphin-insensitive phenotype was verified in fish. Our results provide a molecular explanation for the species selectivity of skin-derived opioid peptides
Structure of the human Îș-opioid receptor in complex with JDTic
Opioid receptors mediate the actions of endogenous and exogenous opioids on many physiological processes, including the regulation of pain, respiratory drive, mood, andâin the case of Îș-opioid receptor (Îș-OR)âdysphoria and psychotomimesis. Here we report the crystal structure of the human Îș-OR in complex with the selective antagonist JDTic, arranged in parallel dimers, at 2.9âĂ
resolution. The structure reveals important features of the ligand-binding pocket that contribute to the high affinity and subtype selectivity of JDTic for the human Îș-OR. Modelling of other important Îș-OR-selective ligands, including the morphinan-derived antagonists norbinaltorphimine and 5âČ-guanidinonaltrindole, and the diterpene agonist salvinorin A analogue RB-64, reveals both common and distinct features for binding these diverse chemotypes. Analysis of site-directed mutagenesis and ligand structureâactivity relationships confirms the interactions observed in the crystal structure, thereby providing a molecular explanation for Îș-OR subtype selectivity, and essential insights for the design of compounds with new pharmacological properties targeting the human Îș-OR