beta-Peptides: from structure to function.

Opioid receptors have been targeted for the treatment of pain and related disorders for thousands of years and remain the most widely used analgesics in the clinic. Mu (μ), kappa (κ), and delta (δ) opioid receptors represent the originally classified receptor subtypes, with opioid receptor like-1 (ORL1) being the least characterized. All four receptors are G-protein coupled and activate inhibitory G proteins. These receptors form homo- and heterodimeric complexes and signal to kinase cascades and scaffold a variety of proteins.The authors discuss classic mechanisms and developments in understanding opioid tolerance and opioid receptor signaling and highlight advances in opioid molecular pharmacology, behavioral pharmacology, and human genetics. The authors put into context how opioid receptor signaling leads to the modulation of behavior with the potential for therapeutic intervention. Finally, the authors conclude there is a continued need for more translational work on opioid receptors in vivo.

Molecular mechanisms of opioid receptor-dependent signaling and behavior.

Protein glycosylation is an important post-translational modification. It is a feature that enhances the functional diversity of proteins and influences their biological activity. A wide range of functions for glycans have been described, from structural roles to participation in molecular trafficking, self-recognition and clearance. Understanding the basis of these functions is challenging because the biosynthetic machinery that constructs glycans executes sequential and competitive steps that result in a mixture of glycosylated variants (glycoforms) for each glycoprotein. Additionally, naturally occurring glycoproteins are often present at low levels, putting pressure on the sensitivity of the analytical technologies. No universal method for the rapid and reliable identification of glycan structure is currently available; hence, research goals must dictate the best method or combination of methods. To this end, we introduce some of the major technologies routinely used for structural N- and O-glycan analysis, describing the complementary information that each provides.

A systematic approach to protein glycosylation analysis: a path through the maze

Stress is a complex human experience having both positive and negative motivational properties. When chronic and uncontrollable, the adverse effects of stress on human health are considerable and yet poorly understood. Here, we report that the dysphoric properties of chronic stress are encoded by the endogenous opioid peptide dynorphin acting on specific stress-related neuronal circuits. Using different forms of stress presumed to evoke dysphoria in mice, we found that repeated forced swim and inescapable footshock both produced aversive behaviors that were blocked by a κ-opioid receptor (KOR) antagonist and absent in mice lacking dynorphin. Injection of corticotropin-releasing factor (CRF) or urocortin III, key mediators of the stress response, produced place aversion that was also blocked by dynorphin gene deletion or KOR antagonism. CRF-induced place aversion was blocked by the CRF2 receptor antagonist antisauvigine-30, but not by the CRF1 receptor antagonist antalarmin. In contrast, place aversion induced by the KOR agonist U50,488 was not blocked by antisauvigine-30. These results suggest that the aversive effects of stress were mediated by CRF2 receptor stimulation of dynorphin release and subsequent KOR activation. Using a phospho-selective antibody directed against the activated KOR to image sites of dynorphin action in the brain, we found that stress and CRF each caused dynorphin-dependent KOR activation in the basolateral amygdala, nucleus accumbens, dorsal raphe, and hippocampus. The convergence of stress-induced aversive inputs on the dynorphin system was unexpected, implicates dynorphin as a key mediator of dysphoria, and emphasizes κ-receptor antagonists as promising therapeutics.

https://www.jneurosci.org/content/jneuro/28/2/407.full.pdf

The Dysphoric Component of Stress Is Encoded by Activation of the Dynorphin κ-Opioid System

https://bpspubs.onlinelibrary.wiley.com/doi/pdf/10.1111/bph.12445

The Concise Guide to PHARMACOLOGY 2013/14: G Protein‐Coupled Receptors

Endogenous opioids seem to play a critical role in the regulation of mood states. For example, there is accumulating evidence that stimulation of κ-opioid receptors, upon which the endogenous opioid dynorphin acts, can produce depressive-like behaviors in laboratory animals. Here we examined whether systemic administration of salvinorin A (SalvA), a potent and highly selective κ-opioid agonist, would produce depressive-like effects in the forced swim test (FST) and intracranial self-stimulation (ICSS) test, which are behavioral models often used to study depression in rats. We extracted, isolated, and purified SalvA from Salvia divinorum plant leaves and examined its effects on behavior in the FST and ICSS test across a range of doses (0.125–2.0 mg/kg) after systemic (intraperitoneal) administration. SalvA dose dependently increased immobility in the FST, an effect opposite to that of standard antidepressant drugs. Doses of SalvA that produced these effects in the FST did not affect locomotor activity in an open field. Furthermore, SalvA dose dependently elevated ICSS thresholds, an effect similar to that produced by treatments that cause depressive symptoms in humans. At a dose that caused the depressive-like effects in both the FST and ICSS assays, SalvA decreased extracellular concentrations of dopamine (DA) within the nucleus accumbens (NAc), a critical component of brain reward circuitry, without affecting extracellular concentrations of serotonin (5-HT). These data provide additional support for the hypothesis that stimulation of brain κ-opioid receptors triggers depressive-like signs in rats and raise the possibility that decreases in extracellular concentrations of DA within the NAc contribute to these effects.

http://www.sagewisdom.org/carlezonetal.pdf

Depressive-Like Effects of the κ-Opioid Receptor Agonist Salvinorin A on Behavior and Neurochemistry in Rats

Synthetic protocols and circular dichroism (CD) spectra are reported for a series of oligomers of (R,R)-trans-2-aminocyclopentanecarboxylic acid (trans-ACPC). The two longest oligomers, a hexamer and an octamer, have also been examined crystallographically. Both crystal structures show that the β-peptide backbone adopts a regular helix that is defined by a series of interwoven 12-membered ring hydrogen bonds (“12-helix”). Each hydrogen bond links a carbonyl oxygen to an amide proton three residues toward the C-terminus. CD data suggest that the conformational preference of trans-ACPC oligomers in methanol is strongly length-dependent, which implies that 12-helix formation is a cooperative process, as seen for the α-helix formed by conventional peptides. Previous work has established that oligomers and polymers of β-amino acids can adopt helical conformations, but the 12-helix is an unprecedented β-peptide secondary structure.

Synthesis and Structural Characterization of Helix-Forming β-Peptides: trans-2-Aminocyclopentanecarboxylic Acid Oligomers

The thermodynamically less stable form of galactose-galactofuranose (Galf)-is essential for the viability of several pathogenic species of bacteria and protozoa but absent in this form in mammals, so the biochemical pathways by which Galf-containing glycans are assembled and catabolysed are attractive sites for drug action This potential has led to increasing interest in the synthesis of molecules containing Galf residues, their subsequent use in studies directed towards understanding the enzymes that process these residues and the identification of potential inhibitors of these pathways Major achievements of the past several years have included an in-depth understanding of the mechanism of UDP-galactopyranose mutase (UGM), the enzyme that produces UDP-Galf, which is the donor species for galactofuranosyltransferases A number of methods for the synthesis of galactofuranosides have also been developed, and practitioners in the field now have many options for the initiation of a synthesis of glycoconjugates containing either alpha- or beta-Galf residues UDP-Galf has also been prepared by a number of approaches, and it appears that a chemoenzymatic approach is currently the most viable method for producing multi-milligram amounts of this important intermediate Recent advances both in the understanding of the mechanism of UGM and in the synthesis of galactofuranose and its derivatives are highlighted in this review

Chemistry and biology of galactofuranose-containing polysaccharides.

Conformational analysis of furanoside-containing mono- and oligosaccharides.

Bacterial capsules are surface layers made of long-chain polysaccharides. They are anchored to the outer membrane of many Gram-negative bacteria, including pathogens such as Escherichia coli, Neisseria meningitidis, Haemophilus influenzae, and Pasteurella multocida. Capsules protect pathogens from host defenses including complement-mediated killing and phagocytosis and therefore represent a major virulence factor. Capsular polysaccharides are synthesized by enzymes located in the inner (cytoplasmic) membrane and are then translocated to the cell surface. Whereas the enzymes that synthesize the polysaccharides have been studied in detail, the structure and biosynthesis of the anchoring elements have not been definitively resolved. Here we determine the structure of the glycolipid attached to the reducing terminus of the polysialic acid capsular polysaccharides from E. coli K1 and N. meningitidis group B and the heparosan-like capsular polysaccharide from E. coli K5. All possess the same unique glycolipid terminus consisting of a lyso-phosphatidylglycerol moiety with a β-linked poly-(3-deoxy-d-manno-oct-2-ulosonic acid) (poly-Kdo) linker attached to the reducing terminus of the capsular polysaccharide.

https://www.pnas.org/content/pnas/110/19/7868.full.pdf

Michele R. Richards

Papers

Depressive-Like Effects of the κ-Opioid Receptor Agonist Salvinorin A on Behavior and Neurochemistry in Rats

Synthesis and Structural Characterization of Helix-Forming β-Peptides: trans-2-Aminocyclopentanecarboxylic Acid Oligomers

Chemistry and biology of galactofuranose-containing polysaccharides.

Conformational analysis of furanoside-containing mono- and oligosaccharides.

Conserved glycolipid termini in capsular polysaccharides synthesized by ATP-binding cassette transporter-dependent pathways in Gram-negative pathogens