A single residue, aspartic acid 95, in the delta opioid receptor specifies selective high affinity agonist binding

The enkephalins, dynorphins, and endorphins are endogenous opioids which function as neurotransmitters, neuromodulators, and hormones and are involved in the perception of pain, modulation of behavior, and regulation of autonomic and neuroendocrine function. Pharmacological studies have defined three classes of opioid receptors, designated as delta, kappa, and mu. To investigate mechanisms by which agonists and antagonists interact with the delta opioid receptor, we have substituted aspartic acid 95 in the transmembrane segment 2 of the cloned mouse delta opioid receptor with an asparagine (D95N). The D95N mutant receptor had reduced affinity for delta receptor-selective agonists such as enkephalin, [D-Pen2,D-Pen5]enkephalin and [D-Ser2,Leu5]enkephalin-Thr6 such that it did not bind these peptides even at micromolar concentrations. The binding of delta-selective non-peptide agonists was also reduced. In contrast, the delta receptor-selective antagonists, such as naltrindole, the benzofuran analog of naltrindole, and 7-benyllidenenaltrexone, bound equally well to the wild-type and mutant receptor. Similarly, non-selective opioid agonists such as bremazocine and buprenorphine, which interact with delta, kappa, and mu opioid receptors, showed no difference in binding to the wild-type and mutant delta receptor. The D95N mutant remained coupled to G proteins, and the receptor was functionally active since it mediated agonist inhibition of cAMP accumulation. These results indicate that selective agonists and antagonists bind differently to the delta receptor and show that Asp-95 contributes to high affinity delta-selective agonist binding. The identification of a key residue involved in selective agonist binding to the delta opioid receptor will facilitate the development of novel therapeutic reagents that can be used for the treatment of chronic pain and other conditions.

Splice variant of the somatostatin receptor 2 subtype, somatostatin receptor 2B, couples to adenylyl cyclase

The diverse biological actions of somatostatin (SRIF) are mediated by a family of receptors, of which five have been cloned and characterized. One of the SRIF receptor subtypes, SSTR2, has been shown to exist in two forms. SSTR2A and SSTR2B are 369 and 346 amino acids in size, respectively, and differ in length and amino acid sequence in their intracellularly located carboxyl termini. SSTR2A and SSTR2B are generated by alternative splicing of SSTR2 mRNA. We previously characterized mouse SSTR2A and showed that it could be distinguished from other cloned SRIF receptor subtypes by its high affinity for MK-678 and its lack of coupling to adenylyl cyclase. To determine whether the properties of mouse SSTR2A and SSTR2B differ, we have expressed both in COS-7 cells and characterized their ligand-binding properties and ability to couple to adenylyl cyclase. The two receptors exhibited similar affinities for a number of SSTR2-selective agonists such as MK-678. Pretreatment with SRIF of COS-7 cells expressing each receptor reduced high affinity agonist binding to both SSTR2A and SSTR2B, indicating that both receptors can be regulated. Furthermore, agonist binding to both receptors was reduced by GTP analogs and Na+, indicating that they both associate with G proteins. As shown previously, SSTR2A could not mediate SRIF inhibition of forskolin-stimulated cAMP formation. In contrast, SSTR2B was coupled to adenylyl cyclase and was able to mediate SRIF inhibition of forskolin-stimulated cAMP formation. Thus, SSTR2A and SSTR2B differ in their ability to couple to adenylyl cyclase. Because SSTR2A and SSTR2B differ only in the length and amino acid sequence of their carboxyl termini, these findings imply that the carboxyl-terminal 15 residues of SSTR2B may be involved in coupling this receptor to adenylyl cyclase.

Mutation of an aspartate at residue 89 in somatostatin receptor subtype 2 prevents Na+ regulation of agonist binding but does not alter receptor-G protein association

Sodium ions have been shown to reduce the binding of agonists to a number of G protein-linked receptors. They are believed to do so by interacting with aspartate residues in the second membrane-spanning region of these receptors to cause G protein uncoupling, resulting in a diminished affinity of the receptors for agonists. To investigate Na+ regulation of agonist binding to somatostatin receptors, Na+ was tested for its effect on the binding of agonists to cloned somatostatin receptor type 1 (SSTR1) and somatostatin receptor type 2 (SSTR2) stably expressed in Chinese hamster ovary cells. Na+ reduced agonist binding to SSTR2 but not to SSTR1. Because high affinity agonist binding to SSTR1 does not depend on G protein coupling but agonist binding to SSTR2 is reduced by guanosine-5'-(beta, gamma-imido)triphosphate and pertussis toxin treatment, the selective Na+ effect on SSTR2 is consistent with previous findings with other receptors showing that Na+ uncouples receptors from G proteins, thereby reducing the affinity of the receptors for agonists. Conversion of Asp89 to Asn89 in SSTR2 resulted in a mutant receptor whose affinity for agonists was not altered by Na+, indicating that Asp89 is involved in mediating the effects of Na+ on agonist binding to SSTR2. However, the affinities of the mutant and wild-type receptors for somatostatin were the same, and both guanosine-5'-O-(gamma-thio)triphosphate and pertussis toxin treatment reduced agonist binding to the mutant and wild-type receptors. These findings differ from the results of similar mutagenesis studies on other G protein-linked receptors, in that the mutant and wild-type SSTR2 forms associate with G proteins in similar ways. These results indicate that Asp89 acts in a novel manner to regulate agonist binding and G protein interaction with SSTR2.

Characterization of cloned somatostatin receptors SSTR4 and SSTR5

The recent molecular cloning of the genes and cDNAs encoding multiple somatostatin (SRIF) receptor subtypes has allowed for the individual expression of these receptors in mammalian cells and characterization of their respective pharmacological profiles. Previously, we fully described and compared the pharmacological properties of the first three SRIF receptor subtypes, SRIF receptor type (SSTR)1, SSTR2, and SSTR3. In the present study, we have investigated the properties of the newly cloned SRIF receptor subtypes SSTR4 and SSTR5 with regard to pharmacological profiles, the regulation of high affinity agonist binding to these receptors by stable GTP analogues, Na+, or prior exposure to agonists, and the inhibition of forskolin-stimulated cAMP accumulation mediated by these receptors. We labeled SSTR4 and SSTR5 expressed in Chinese hamster ovary (CHO-K1) and COS-1 cells, respectively, with the metabolically stable SRIF analogue 125I-CGP 23996. Radioligand binding competition studies were performed using SRIF analogues of differing structures, including hexapeptide analogues similar to MK-678, octapeptide analogues similar to SMS 201-995, pentapeptide analogues similar to c[Ahep-Phe-D-Trp-Lys-Thr(Bzl)], and linear SRIF analogues. SSTR4 bound compounds in all structural classes with high to moderate affinities, and several compounds were identified that are > 100-fold selective for SSTR4, compared with the other cloned SRIF receptors, including the linear SRIF analogue BIM-23052 and the CGP 23996-like SRIF analogue L-362,855. In contrast, SSTR5 bound very few SRIF analogues with high affinity. Both receptors could be regulated by prior exposure to agonist. In addition, agonist binding to SSTR4 was reduced by stable GTP analogues, Na+, and pertussis toxin, but agonist binding to SSTR5 was not affected by these treatments. SSTR4 is efficiently coupled to the inhibition of adenylyl cyclase activity, whereas SSTR5 appears not to couple to this cellular effector system. Such differences between the cloned SRIF receptors provide useful strategies for identifying regions of these receptor subtypes that may be involved in ligand-binding specificities and G protein and cellular effector system coupling. The identification of subtype-selective SRIF analogues may lead to more specific therapeutic interventions.

Cloning and functional comparison of kappa and delta opioid receptors from mouse brain

While trying to identify new members of the somatostatin receptor family of G protein-coupled receptors, we isolated cDNAs from a mouse brain library encoding two related receptor-like proteins, designated msl-1 and msl-2, of 380 and 372 amino acids, respectively. There was 61% identity and 71% similarity between the sequences of msl-1 and msl-2. Among members of the G protein-coupled receptor superfamily, the sequences of both msl-1 and msl-1 were most closely related to those of the somatostatin receptors (SSTRs), having approximately 35% identity with the sequence of SSTR1. Transient expression in COS-1 cells showed that msl-1 and msl-2 did not bind somatostatin. Rather they bound opioids selectively and with high affinity and had the pharmacological properties of kappa and delta opioid receptors, respectively. Indeed, the sequence of msl-2 was identical to that of a delta opioid receptor recently cloned by other workers. Functional characterization of kappa/msl-1 and delta/msl-2 opioid receptors showed that they were coupled to G proteins and mediated opioid receptor class-specific agonist inhibition of forskolin-stimulated cAMP formation. RNA blotting studies and in situ hybridization histochemistry showed that kappa opioid receptor mRNA was expressed at high levels in brain in the neocortex, hippocampus, amygdala, medial habenula, hypothalamus (arcuate and paraventricular nuclei), locus ceruleus, and parabrachial nucleus, suggesting that this receptor may play a role in arousal and regulation of autonomic and neuroendocrine functions.

A unique restriction endonuclease, BcgI, from Bacillus coagulans

We have purified and characterized a new restriction endonuclease, BcgI, which has properties unlike those of the three recognized classes of restriction enzymes. BcgI was isolated from Bacillus coagulans, and it recognizes the sequence CGAN6TGC. BcgI cleaves double stranded DNA on both strands upstream and downstream of the recognition sequence, so that the recognition sequence is released as a 34-base pair fragment with 2-base 3'-extensions. Mg++ and S-adenosylmethionine are required for cleavage. Sinefungin, a structural analogue of AdoMet which generally inhibits methylase activity, can replace AdoMet in the cleavage reaction. The apparent binding constant (Kappd) for AdoMet is about 100 nM, while the KappD for sinefungin is about 500 nM.

Lipoperoxidative damage in experimental rabbits with atherosclerosis

The extent of lipoperoxidation in experimental rabbits with atherosclerosis was determined dynamically during the experimental period of 65 days. Lipoperoxide (LPO) levels and selenium-dependent glutathions peroxidase (SeGSHPx) activities in liver, aorta, heart muscle, plasma erythrocyte (RBC) and platelet were examined on the 65th day. The results showed that the potential anti-lipoperoxidation in the atherosclerotic rabbits was decreased significantly, and the tissues were suffered from lipoperoxidative damage. It seems that there is a close relationship between lipoperoxidative damage and the development of atherosclerosis.

Characterization of a DNA polymerase from the hyperthermophile archaea Thermococcus litoralis. Vent DNA polymerase, steady state kinetics, thermal stability, processivity, strand displacement, and exonuclease activities

We have isolated, cloned, and characterized a DNA polymerase from the hyperthermophile archaea Thermococcus litoralis, the Tli DNA polymerase (also referred to as Vent DNA polymerase). The enzyme is extremely thermostable, having a half-life of 8 h at 95 degrees C and about 2 h at 100 degrees C. Pseudo-first-order kinetics at 70 degrees C reveal an extremely low Km for a primed M13mp18 substrate (0.1 nM), coupled with a relatively high Km for dNTPs (50 microM). Accompanying extension rates are on the order of 1000 nucleotides/min. Synthesis by the polymerase is largely distributive, adding an average of 7 nucleotides/initiation event. This distributive synthesis can generate products of at least 10,000 bases. Tli DNA polymerase contains a 3'-->5' exonuclease activity that enhances the fidelity of replication by the enzyme (Mattila, P., Korpela, J., Tenkanen, T. and Pitkanen, K. (1991) Nucleic Acids Res. 19, 4967-4973). A 2-amino acid substitution within the conserved exonuclease domain abolishes both double and single strand-dependent exonuclease activity, without altering kinetic parameters for polymerization on a primed single-stranded template. Strand displacement activity by the mutated and unmutated forms increases with increasing temperature and is enhanced in the exonuclease-deficient form of the enzyme.

Experimental study of achromatic volume holography with dispersive compensation in barium titanate

We carried out an experimental study to verify a proposed theory for achromatic volume holography using dispersive compensation in photorefractive barium titanate crystals. Compensation of the phase mismatch was observed and was consistent with the theory.

Femtosecond temporal encoding in barium titanate

We describe two-beam coupling and temporal encoding experiments in barium titanate. Volume gratings are created in the photorefractive material by 50-fs optical pulses. Information in the writing pulses may be encoded as spatially distributed volume gratings in the crystal. Femtosecond temporal waveform reconstruction is demonstrated.

Photorefractive two-beam coupling with reduced spatiotemporal coherence

Photorefractive two-beam coupling with reduced spatiotemporal coherence is investigated both theoretically and experimentally. Limited spatiotemporal coherence results in spatially limited grating regions. Theoretical predictions of the beam-coupling behavior in two symmetries are supported by experimental results.

Identification of a new type II restriction endonuclease, BsaAI

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Female gene expression in the seminal vesicle of mice after prenatal exposure to diethylstilbestrol

Previous studies from our laboratory on the feminization of the male mouse reproductive tract after prenatal exposure to diethylstilbestrol (DES) showed that the mRNA for the major estrogen-inducible uterine secretory protein, lactoferrin (LF), was constitutively expressed in the seminal vesicle of male mice exposed prenatally to DES, but not in the seminal vesicle of control mice. After castration, treatment with 17 beta-estradiol (20 micrograms/kg.day) for 3 days induced the LF mRNA in the seminal vesicle of both control and prenatally DES-exposed mice; however, the levels in DES-treated tissues were approximately 6-fold higher than those in control tissue. This report describes the presence of LF in seminal vesicle tissues and secretions of prenatally DES-exposed mice, as determined by immunohistochemistry and Western blot analysis. Further, these data are correlated with immunolocalization of the estrogen receptor in the seminal vesicle tissue. We conclude that the seminal vesicle of prenatally DES-exposed male mice has acquired two key characteristics of female tissues, namely LF production/regulation and estrogen receptor localization/distribution similar to that in uterine tissues.

Photorefractive phase conjugation with orthogonally polarized pumping beams

We solve the undepleted-pumps photorefractive four-wave mixing equations for the case of orthogonally polarized pump beams. Advantages over the parallel-polarized-pumps case include the potential for reflectivity enhancement and easy isolation of the conjugator from the source. The phase-conjugate reflectivities for both the parallel and orthogonally polarized pump beam cases were measured with a BaTiO3 crystal, and the results support our theoretical predictions.

Photorefractive time differentiation of coherent optical images

Two-beam coupling in photorefractive BaTiO(3) is used to perform time differentiation of time-varying coherent phase and amplitude images. Differentiation of one-dimensional signals and two-dimensional images is performed.