Receptor最新文献

The role of protein kinase C (PKC) in the signaling mechanism that stimulates the release of mediators from rat mast cells, for which the RBL-2H3 cell line is a model, is at present unresolved. Current evidence suggests that PKC activation alone is an insufficient stimulus, although it can modulate mast cell exocytosis induced by other agents. In this article we characterize a variant of the RBL-2H3 cell line that has a reduced capacity for mediator secretion in response to an IgE-mediated antigen-induced stimulation. The outcome of our study suggests that at least two PKC isotypes are active in RBL-2H3 cells, and affect the positive and negative modulation of the secretory response.

Parallel synthesis and testing procedures are being investigated to shorten the drug design and discovery process. These procedures have focused on peptides and nucleotides, although these compounds are unlikely to be useful therapeutics because of their low bioavailability and sensitivity to enzymatic degradation. More recently, the use of other modular systems with distinct linking chemistries have been explored. Structural data combined with computational screens of compound databases provides an alternative method to identify novel nonpeptide pharmaceuticals. When structural information is not available, homology-based models have proved to be sufficient to identify nonpeptide inhibitors active at low micromolar concentrations against important enzymes in parasite life cycles.

A growing body of literature exists documenting the nonnuclear effects of steroid hormones, and in particular, binding of the lipophillic ligands to specific plasmalemmal recognition sites. This review compiles evidence supporting the presence of membrane receptors for extradiol 17 beta, progesterone, corticosteroids, thyroid hormone, and 1,25-dihydroxyvitamin D3. In addition, 1,25-dihydroxyvitamin D3-mediated nonnuclear signal transduction mechanisms and physiological responses are discussed.

The proto-oncogenic and oncogenic forms of the rat neu receptors were expressed in the baculovirus system to characterize their structural and enzymatic differences. The epitopes of their extracellular domains, their molecular weights, and kinase activities were similar to rat neu receptors expressed in fibroblasts. The receptors were partially purified using a phospho-agarose column and were analyzed to compare kinetic parameters using ATP as a substrate. The oncogenic form of the receptor showed a significant increase in Vmax (56%) over the proto-oncogenic form. Structural analysis of these proteins using sucrose gradients showed the oncogenic receptors to have a 62.6% increase in aggregated receptors when compared to the proto-oncogenic receptors. These studies are the first to link enzymatic activation and the physical form of the receptor using isolated receptor species.

Protein kinase C (pKC) activity has been studied in rat liver after subjecting animals to heat shocking. Nuclear pKC activity was stimulated owing to heat shocking without any change in the cytosolic enzyme activity. The nuclear diacylglycerol levels were raised owing to heat stress along with the stimulation of polarhead phospholipid hydrolysis. Kinetically, the Vmax of nuclear pKC was enhanced as a result of heat shocking, with no change in apparent Km and with concomitant phosphorylation of nuclear lamin B2. Western blot analysis as well as phorbol dibutyrate binding indicate that pKC protein levels did not change because of heat shocking. The stimulation of nuclear pKC under heat stress conditions represents an in vivo phenomenon and the enzymes stimulation precedes Hsp70 mRNA expression.

The beta-adrenergic receptor kinases, beta ARK1 and beta ARK2, are two recently cloned members of the G protein-coupled receptor kinase family. To further characterize these kinases, bovine beta ARK1 and beta ARK2 have been overexpressed in Sf9 insect cells using the baculovirus expression system. High yields (5-7 mg/L cells) of purified kinase preparations were obtained by sequential chromatography of infected Sf9 cell supernatant fractions on S-Sepharose and Heparin-Sepharose. The expressed kinases were fully active as evidenced by their ability to specifically phosphorylate the agonist-occupied beta 2-adrenergic receptor (beta 2AR) and light-activated rhodopsin. Similar initial rates and maximal stoichiometries of beta 2AR phosphorylation were observed for both beta ARK1 and beta ARK2. Moreover, G protein beta gamma subunits enhanced the initial rates of both beta ARK1 and beta ARK2 mediated beta 2AR phosphorylation by approximately tenfold. In the presence of beta gamma subunits the maximal stoichiometry of beta 2AR phosphorylation was increased from approximately 4 mol phosphate/mol receptor to approximately 10 mol/mol. Detailed kinetic analysis of rhodopsin phosphorylation suggests that both kinases follow a sequential mechanistic pathway and have similar Kms for rhodopsin (approximately 14 microM) and MgATP (60-90 microM). Peptide phosphorylation studies demonstrate that both kinases prefer acidic amino acids amino terminal to a serine. Heparin was found to be the most potent inhibitor for both kinases with IC50s of 1.4 and 1.1 microM for beta ARK1 and beta ARK2, respectively. These studies demonstrate that beta ARK1 and beta ARK2 share very similar kinetic properties and suggest that they may have a similar substrate specificity in vivo.

An analysis of the stereochemistry of hydrogen bonding and metal binding to some nitrogen-containing heterocycles found in crystal structure determinations has shown that the interacting atom will generally lie in the plane of the heterocyclic ring system in a direction that approximately bisects the C-N-C angle of the heterocycle. The Cambridge Structural Database (CSD) of crystal structures of small molecules was used for this analysis because stereochemical data are available at high resolution and are amendable to comparative analysis. It was found that, for hydrogen bonding, a slight out-of-plane deviation of the binding atom is marginally more likely than an in-plane deviation. Metal ions appear to bind in a manner that is similar to that of hydrogen bonding to a protonated heterocycle, no matter what the chemical identity of the metal. The binding is more rigid, with less in-plane or out-of-plane deviation of the metal ion compared to the interaction with a hydrogen-bonding group. Some ab initio molecular orbital energy calculations give a measure of the energies involved when metal ions or hydrogen-bonding groups deviate from the plane of the ring system or from the line bisecting the C-N-C angle of the heterocycle. These results are compared with reported structural data (at lower resolution) for some acridine-oligonucleotide complexes and the surroundings of histidine rings in some protein crystal structures.

Congenital adrenal hyperplasia (CAH) results from enzymatic blocks in the synthesis of cortisol. All enzyme defects causing CAH are autosomal recessive traits. It is a relatively common disease, occurring in 1 in 5000 to 1 in 15,000 births in most populations. Since the isolation of the gene responsible for steroid 21-hydroxylase deficiency (involved in about 90% of the cases of CAH) in 1984, knowledge of the specific mutations that cause the different forms of CAH has grown rapidly. Mutations in the encoding gene have been confirmed as the basis of endocrine disease in the case of all of the adrenal steroidogenic enzymes required for synthesis of cortisol but one (cholesterol desmolase). The clinical expression of endocrine disease is not always correlated with the mutations of the primary structural gene. Clinicians cannot accurately predict the course of the disease or make therapeutic decisions based on the genotype alone. We will review the various forms of clinical presentation of CAH, their etiology, diagnosis, molecular genetics, and treatment.

The relationships between parasites and hosts are complex, with many of these interactions involving an amazing degree of biochemical coevolution and communication. Hormones, neurohormones, and growth factors figure prominently in these relationships. In vertebrate hosts, many parasites secrete hormones, neuropeptides, or cytokine-like molecules that influence the host's physiological and immunological responses. Alternatively, the parasites secrete factors that alter the host's hormone levels. Simultaneously, molecules emanating from the host strongly influence the parasites' success. In some cases the host's hormones directly influence the parasites; in others, effects are mediated indirectly via the host's immune system. In invertebrates, the presence of parasites likewise has a major influence on the host's endocrine status and the normal suite of processes governed by hormones, including host development, metamorphosis, and reproduction. In insects, interactions involving juvenile hormone and ecdysteroids are especially well-documented, and recent evidence suggests that neuropeptides may also be affected by parasitism. Moreover, recent data suggest that in some species, such as snails, the host's nervous, neuroendocrine, and immune systems are functionally linked, similar to the complex interactions seen in vertebrates.

Although steroid hormone receptors constitute an intensively studied family of ligand-regulated transcription factors, the mechanism by which these receptors activate transcription has not been defined. Evidence has accumulated from prokaryotic and eukaryotic systems that many transcription factors are capable of binding to their cognate recognition sequences and causing DNA to bend. Therefore, it has been hypothesized that DNA bending and transcription activation may be functionally coupled. We have utilized circular permutation analysis to examine the ability of the estrogen receptor DNA binding domain and the intact estrogen receptor to bend DNA fragments containing estrogen response elements (EREs). The DNA binding domain, which is a less potent activator of transcription, bent ERE containing DNA fragments less (34 degrees) than the intact estrogen receptor (56 degrees), which is a more potent activator of transcription. In addition, when two EREs were present in a DNA fragment, the degree of DNA bending observed was greater than when one ERE was present. These data suggest that DNA bending may play a role in transcription activation of estrogen responsive genes.