Quantifying agonist activity at G protein-coupled receptors

When an agonist activates a population of G protein-coupled receptors (GPCRs), it elicits a signaling pathway that culminates in the response of the cell or tissue. This process can be analyzed at the level of a single receptor, a population of receptors, or a downstream response. Here we describe how to analyze the downstream response to obtain an estimate of the agonist affinity constant for the active state of single receptors. Receptors behave as quantal switches that alternate between active and inactive states (Figure 1). The active state interacts with specific G proteins or other signaling partners. In the absence of ligands, the inactive state predominates. The binding of agonist increases the probability that the receptor will switch into the active state because its affinity constant for the active state (K(b)) is much greater than that for the inactive state (K(a)). The summation of the random outputs of all of the receptors in the population yields a constant level of receptor activation in time. The reciprocal of the concentration of agonist eliciting half-maximal receptor activation is equivalent to the observed affinity constant (K(obs)), and the fraction of agonist-receptor complexes in the active state is defined as efficacy (ε) (Figure 2). Methods for analyzing the downstream responses of GPCRs have been developed that enable the estimation of the K(obs) and relative efficacy of an agonist. In this report, we show how to modify this analysis to estimate the agonist K(b) value relative to that of another agonist. For assays that exhibit constitutive activity, we show how to estimate K(b) in absolute units of M(-1). Our method of analyzing agonist concentration-response curves consists of global nonlinear regression using the operational model. We describe a procedure using the software application, Prism (GraphPad Software, Inc., San Diego, CA). The analysis yields an estimate of the product of K(obs) and a parameter proportional to efficacy (τ). The estimate of τK(obs) of one agonist, divided by that of another, is a relative measure of K(b) (RA(i)). For any receptor exhibiting constitutive activity, it is possible to estimate a parameter proportional to the efficacy of the free receptor complex (τ(sys)). In this case, the K(b) value of an agonist is equivalent to τK(obs)/τ(sys). Our method is useful for determining the selectivity of an agonist for receptor subtypes and for quantifying agonist-receptor signaling through different G proteins.     

The genetic profile and molecular diagnosis of thiophanate-methyl resistant strains of Fusarium asiaticum in Japan

Fusarium asiaticum strains resistant to thiophanate-methyl were detected in four prefectures in Japan though their proportion in the total population was low in all instances. The F167Y or F200Y mutation in the β2-tubulin gene (FGSG06611.3) was detected in thiophanate-methyl resistant (TMR) strains. A PCR-based diagnostic method based on these mutations was developed and applied for all 17 TMR strains that have been detected so far in Japan. Three and 14 TMR strains were the F167Y and F200Y mutation types, respectively. Analysis by 11 variable number of tandem repeat markers showed that TMR strains from the same site had an identical genotype, while TMR strains from different sites were dissimilar. This result indicates that TMR strains did not spread clonally to the different sites.     

Flexizymes for genetic code reprogramming

Genetic code reprogramming is a method for the reassignment of arbitrary codons from proteinogenic amino acids to nonproteinogenic ones; thus, specific sequences of nonstandard peptides can be ribosomally expressed according to their mRNA templates. Here we describe a protocol that facilitates genetic code reprogramming using flexizymes integrated with a custom-made in vitro translation apparatus, referred to as the flexible in vitro translation (FIT) system. Flexizymes are flexible tRNA acylation ribozymes that enable the preparation of a diverse array of nonproteinogenic acyl-tRNAs. These acyl-tRNAs read vacant codons created in the FIT system, yielding the desired nonstandard peptides with diverse exotic structures, such as N-methyl amino acids, D-amino acids and physiologically stable macrocyclic scaffolds. The facility of the protocol allows a wide variety of applications in the synthesis of new classes of nonstandard peptides with biological functions. Preparation of flexizymes and tRNA used for genetic code reprogramming, optimization of flexizyme reaction conditions and expression of nonstandard peptides using the FIT system can be completed by one person in approximately 1 week. However, once the flexizymes and tRNAs are in hand and reaction conditions are fixed, synthesis of acyl-tRNAs and peptide expression is generally completed in 1 d, and alteration of a peptide sequence can be achieved by simply changing the corresponding mRNA template.     

Reversing-pulse electric birefringence of poly(γ-benzyl-L-glutamate). III. The temperature dependence of the transient and steady-state behavior in cyclohexanone

The reversing-pulse electric birefringence (RPEB) technique was applied to the study of the temperature effect on the electrooptical and hydrodynamic properties of a fractionated [Glu(OBzl)]_n sample, which is molecularly dissolved in cyclohexanone. The aim was to develop a standard analytical method for thermal denaturation and temperature-induced conformational transitions. The field-on reverse and steady-state signal, and the field-off decay signal, were measured at 535 nm and at a constant low field strength (ca. 3 kV/cm) over a wide temperature range (5–90°C). The steady-state birefringence and the relaxation time in the decay process were also measured at two constant temperatures (5 and 70°C) over a wide field strength range (E ≤ 20 kV/cm). By the combination of these two different sets of RPEB measurements, the unwanted effect of the high pulse field on polymer conformation at elevated temperatures could be minimized. Together with the density and viscosity of cyclohexanone measured between 5 and 95°C, the following quantities could be evaluated: the weight-average permanent dipole moment and polarizability anisotropy, the reduced optical anisotropy factor (Δg/n), the weight-average length, and the degree of polydispersity. All these quantities, except for Δg/n, were found to be almost independent of temperature (5–90°C) and concentration (1.54–4.27 mM).     

Effects of orexins/hypocretins on neuronal activity in the paraventricular nucleus of the thalamus in rats in vitro

Orexin-A (ORX-A) and orexin-B (ORX-B), also called hypocretin-1 and hypocretin-2, respectively, act upon orexin 1 (OX1R) and orexin 2 (OX2R) receptors, and are involved in the regulation of sleep-wakefulness and energy homeostasis. Orexin neurons in the lateral hypothalamic perifornical region project heavily to the paraventricular nucleus of the thalamus (PVT), which is deeply involved in the control of motivated behaviors. In the present study, electrophysiological and cytosolic Ca2+ concentration ([Ca2+]i) imaging studies on the effects of ORX-A and ORX-B on neurons in the PVT were carried out in rat brain slice preparations. ORX-A and/or ORX-B were applied extracellularly in the perfusate. Extracellular recordings showed that about 80% of the PVT neurons were excited dose-dependently by both ORX-A and ORX-B at concentrations of 10(-8) to 10(-6)M, and the increase in firing rate was about three times larger for ORX-B than for ORX-A at 10(-7)M. When both ORX-A and ORX-B were applied simultaneously at 10(-7)M, the increase in firing rate was almost equal to that of ORX-B at 10(-7)M, suggesting that the PVT neurons do not show a high affinity to ORX-A which is expected if they have OX1R receptors. The excitatory effect of ORX-B was seen in low Ca2+ and high Mg2+ ACSF as well as in normal ACSF, and the increase in firing rate was greater in low Ca2+ and high Mg2+ ACSF than in normal ACSF. [Ca2+]i imaging studies demonstrated that [Ca2+]i was increased in about 50% of the PVT neurons by both 10(-7)M ORX-A and ORX-B with a stronger effect for ORX-B, and the increase in [Ca2+]i induced by ORX-B was abolished in Ca2+-free ACSF, suggesting that ORX-B does not release Ca2+ from intracellular Ca2+ stores. Subsequent whole cell patch clamp recordings revealed that an after hyperpolarization seen following each action potential in normal ACSF disappeared in Ca2+-free ACSF, and the mean magnitude of the depolarization induced by ORX-B was same in normal, Ca2+-free and TTX-containing Ca2+-free ACSFs. Furthermore, ORX-B-induced depolarization was reversed to hyperpolarization when membrane potential was lowered to about -97 mV, and an increase of extracellular K+ concentration from 4.25 to 13.25 mM abolished the ORX-B-induced depolarization, indicating that the ORX-B-induced depolarization is associated with an increase in the membrane resistance resulting from a closure of K+ channels. These results suggest that orexins depolarize and excite post-synaptically PVT neurons via OX2R receptors, and that orexin-activated PVT neurons play a role in the integration of sleep-wakefulness and energy homeostasis, and in the control of motivated behaviors.     

Effects of intraplantar injections of nociceptin and its N-terminal fragments on nociceptive and desensitized responses induced by capsaicin in mice

Injection of capsaicin into the hindpaw has been employed as a model of chemogenic nociception in mice. Intraplantar injection of nociceptin (30–240 pmol) produced a significant and dose-dependent antinociceptive activity in the capsaicin test. The nociceptin N-terminal fragments, (1–11) and (1–13), were also active with a potency higher than nociceptin and comparable to nociceptin, respectively. Intraplantar injection of the nociceptin (1–7) fragment had no effect on capsaicin-induced nociception. Antinociception induced by nociceptin or nociceptin (1–13) was reversed significantly by intraplantar co-injection of [Nphe¹]nociceptin (1–13)NH₂, an orphan opioid receptor-like 1 (ORL1) receptor antagonist, whereas local injection of the antagonist did not interfere with the action of nociceptin (1–11). Nociceptin (1–11) was approximately 2.0-fold more potent than naturally occurring peptide nociceptin, and 10-fold more active than intraplantar morphine. Nociceptive licking/biting response to intraplantar injection of capsaicin was desensitized by repeated injections of capsaicin at the interval of 15 min. Desensitization induced by capsaicin was attenuated significantly by co-injection of nociceptin at much lower doses than antinociceptive ED₅₀ for nociceptin. Capsaicin desensitization was also decreased by co-injection of nociceptin (1–11) and (1–13) to a similar extent. The present results indicate that not only nociceptin but also the N-terminal fragment (1–13) possesses a local peripheral antinociceptive action, which may be mediated by peripheral ORL1 receptors. In addition, the difference of the effective doses suggests that the antinociceptive action and inhibition of capsaicin-induced desenitization by nociceptin, nociceptin (1–11) and (1–13), may involve distinct mechanisms at the level of the peripheral nerve terminal.     

Elevation of the Hsp70 chaperone does not effect toxicity in mouse models of familial amyotrophic lateral sclerosis

Mutations in copper/zinc superoxide dismutase (SOD1) account for 10-20% of a familial form of amyotrophic lateral sclerosis (ALS). A common feature of SOD1 mutants is abnormal aggregation of the aberrant SOD1 in neurons and glia. We now report that in ALS transgenic mouse models the constitutively expressed heat shock protein 70 (Hsp70) is mislocalized into aggregates together with mutant SOD1 and ubiquitin. Forcing increased synthesis of Hsp70 ameliorates both aggregate formation and toxicity in primary motor neurons in culture. However, chronic increase in an inducible form of Hsp70 to about 10-fold its normal level is shown here not to affect disease course or pathology developed in mice from accumulation of any of three familial ALS causing SOD1 mutants with different underlying biochemical characteristics. Therefore, increasing Hsp70 to a level that is protective in mouse models of acute ischemic insult and selected neurodegenerative disorders is not sufficient to ameliorate mutant SOD1-mediated toxicity.     

Programmable ribozymes for mischarging tRNA with nonnatural amino acids and their applications to translation

Here we describe a novel technology that allows users to charge nonnatural amino acids onto any tRNA. This technology is based on a resin-immobilized ribozyme system, called Flexiresin. It enables users to readily and rapidly synthesize misacylated tRNAs with a wide variety of phenylalanine analogs. Since Flexiresin is reusable and little effort is necessary for regeneration, it is economical and convenient. Moreover, it can adapt to virtually any tRNA chosen by the user, and can therefore be applied to not only a single site mutation but also multiple sites with designated nonnatural amino acids when both the amber and programmed frame-shift mutations are utilized. The original ribozyme utilized for Flexiresin was artificially generated in vitro, and thus the technology in principle could be broadened from Phe analogues to essentially any amino acid.     

Structural elucidation of A-74528, an inhibitor for 2',5'-phosphodiesterase isolated from Streptomyces sp

A-74528 (1) is a metabolite of Streptomyces sp. discovered in the screening for 2',5'-oligoadenylate phosphodiesterase inhibitors. The planar structure of 1 was mainly elucidated by NMR techniques including natural abundance INADEQUATE, and the relative configuration and the conformation were elucidated by the analyses of NOEs and assessment of dihedral angles predicted by QUANTA/CHARMm computations and coupling constants. It was proved that 1 is a highly fused polyketide with a side-chain branching site that never appeared before from the nature.