Palmitoylation and membrane cholesterol stabilize μ-opioid receptor homodimerization and G protein coupling

<p>Abstract</p> <p>Background</p> <p>A cholesterol-palmitoyl interaction has been reported to occur in the dimeric interface of the β₂-adrenergic receptor crystal structure. We sought to investigate whether a similar phenomenon could be observed with μ-opioid receptor (OPRM1), and if so, to assess the role of cholesterol in this class of G protein-coupled receptor (GPCR) signaling.</p> <p>Results</p> <p>C3.55(170) was determined to be the palmitoylation site of OPRM1. Mutation of this Cys to Ala did not affect the binding of agonists, but attenuated receptor signaling and decreased cholesterol associated with the receptor signaling complex. In addition, both attenuation of receptor palmitoylation (by mutation of C3.55[170] to Ala) and inhibition of cholesterol synthesis (by treating the cells with simvastatin, a HMG-CoA reductase inhibitor) impaired receptor signaling, possibly by decreasing receptor homodimerization and Gαi2 coupling; this was demonstrated by co-immunoprecipitation, immunofluorescence colocalization and fluorescence resonance energy transfer (FRET) analyses. A computational model of the OPRM1 homodimer structure indicated that a specific cholesterol-palmitoyl interaction can facilitate OPRM1 homodimerization at the TMH4-TMH4 interface.</p> <p>Conclusions</p> <p>We demonstrate that C3.55(170) is the palmitoylation site of OPRM1 and identify a cholesterol-palmitoyl interaction in the OPRM1 complex. Our findings suggest that this interaction contributes to OPRM1 signaling by facilitating receptor homodimerization and G protein coupling. This conclusion is supported by computational modeling of the OPRM1 homodimer.</p

Identifying the connection between Roman Conceptions of ‘Pure Air’ and Physical and Mental Health in Pompeian Gardens (c. 150 BC-AD 79): A Multi-Sensory Approach to Ancient Medicine

Different genres of Roman literature commented on the relationship between the condition of the environment and physical and mental health. They often refer to clear, pure, or good air as a beneficial aspect of the environment. Yet, unlike fetid air, they provide few descriptions of what constituted healthy air quality. Moreover, aside from pointing out the association between the environment and bodily condition, the writers also did not explain precisely how the link between the two was made. This paper utilizes a comparative study of ancient literature and the archaeological remains of Roman gardens in Pompeii: archaeobotanical samples, fresco paintings, location, and surviving features. Three questions are addressed in this study: First, how did the Romans identify and define pure? Second, how did air connect to the body? Third, what were the qualities of pure air and how did they benefit the body? Not only was inhalation a means of linking air to the body, but the two were also related through sensory perception. I argue that sight, sound, and olfaction were used to identify the qualities of pure air. Through the sensory process of identification, the beneficial properties of pure air were, in accordance with ancient perceptions of sensory function, taken into the body and affected health. Thus, sensory perception acted as the bridge between the environment and health

Antagonist efficacy in MORS196L mutant is affected by the interaction between transmembrane domains of the opioid receptor. J Pharmacol Exp Ther

ABSTRACT In a previous study, we demonstrated that antagonists such as naloxone or naltrexone acted as full agonists at the -opioid receptor (MOR)/␦-opioid receptor (DOR) chimeric receptor (␦2, where the DOR sequence from the first extracellular loop to the carboxyl terminus was spliced to the MOR sequence) when a conserved serine residue in transmembrane 4 (TM4) was mutated to leucine. However, when Ser 196 in the TM4 of MOR was mutated to Leu, antagonists exhibited partial agonistic properties. Since molecular modeling studies suggested transmembrane movement during receptor activation, the observed partial agonistic properties could be due to TM1 and TM7 interaction. Hence, MOR/DOR chimeric mutant receptors with the MOR TM1 and TM7 sequence (␦ 2 7 S196L) or with the MOR TM1 and TM6/7 sequence (␦ 2 67 S196L) were constructed to test such a hypothesis. Using four tests of opioid receptor activation, we found that the opioid antagonists were full agonists in chimeric mutant receptor if the TM1 and TM7 were from different opioid receptors. Additionally, when two of the TM7 amino acid residues of MORS196L receptor mutants were mutated (T327A and C330S), resulting in a mutant receptor with DOR TM7 sequence, opioid antagonist naloxone exhibited full agonistic properties. These data suggest that the efficacy of opioid antagonists in the Ser 196 mutant can be affected by the interaction between TM1 and TM7