Mapping the human membrane proteome: a majority of the human membrane proteins can be classified according to function and evolutionary origin

Background  

Membrane proteins form key nodes in mediating the cell's interaction with the surroundings, which is one of the main reasons why the majority of drug targets are membrane proteins.     

Pharmacologic properties of CDB(VA)-2914

CDB(VA)-2914 (17alpha-acetoxy-11beta-(4-N,N-dimethylaminophenyl)-19-norpregna-4,9-diene-3,20-dione) is a synthetic steroid that demonstrates potent progesterone antagonist activity in vitro and in vivo. Its binding and antagonist potency with respect to the glucocorticoid receptor is significantly reduced compared to that of mifepristone, indicating that CDB(VA)-2914 belongs to a new class of dissociated progesterone receptor modulators that have reduced antiglucorticoid activity. The pharmacological effects of CDB(VA)-2914 have been examined in a variety of animal models, the results of which are reviewed in this paper. CDB(VA)-2914 inhibits ovulation in rats in a dose-dependent manner upon single-dose oral administration and exhibits antifertility activity during continuous low-dose administration. CDB(VA)-2914 is also effective in animal models of postcoital contraception. This paper also presents the results of metabolism studies undertaken to link the results of the animal models to potential human applications. Because of its unique pharmacological profile, CDB(VA)-2914 is a promising candidate for use in contraception as well as treatment of uterine fibroids and endometriosis.     

EGFP-Tagged Vasopressin Precursor Protein Sorting Into Large Dense Core Vesicles and Secretion From PC12 Cells

1. Hypothalamic magnocellular neurons synthesize, store, and secrete large quantities of the neuropeptides, vasopressin (VP) and oxytocin (OT), which are synthesized as protein precursors also containing proteins called neurophysins. These protein precursors are sorted through the regulated secretory pathway (RSP), packaged into large dense core vesicles LDCVs, and their peptide products are secreted from nerve terminals in the posterior pituitary.2. It has been hypothesized that this efficient packaging is dependent on the interaction of the peptide with neurophysin in a complex that forms the granule core. To test this, PC12 cells were transfected with vasopressin precursor DNA constructs that either contained or deleted the neurophysin moiety and tagged with enhanced green fluorescent protein (EGFP) as reporters. The intracellular routing and secretion of the EGFP-tagged VP precursor proteins were studied by in differentiated PC12 cells by fluorescence microscopy, electron microscopic immunocytochemistry, and fluorescent imaging techniques.3. The data showed that only when the neurophysin was present in the VP precursor construct did the fluorescent fusion protein become routed to the RSP and get efficiently packaged into LDCVs and secreted. These data are consistent with the view that routing of the precursor to LDCVs requires the amino acids that encode the intravesicular chaperone, neurophysin.     

Covalent coupling of microorganisms to a cellulosic support

Methods for the covalent coupling of microorganisms to a solid support were investigated. Both bacteria and yeast were attached to cellulose particles using cyanuric chloride as the coupling agent, although different experimental procedures were needed for the two types of microbes. This general technique for whole-cell immobilization offers an advantage over entrapment methods in that the cells are attached to the outer surface of the solid, thus eliminating the resistance of a gel to the transfer of nutrients and products. There are also indications that such immobilized cells show high productivities.     

Purification and characterization of a paired basic residue-specific prohormone-converting enzyme from bovine pituitary neural lobe secretory vesicles

The neuropeptides arginine vasopressin and oxytocin are generated from their prohormones in the hypothalamoneurohypophysial system by enzymatic cleavages at paired basic residues (i.e. Lys-Arg). This study describes the purification of an enzyme from bovine neural lobe secretory vesicles, the putative site of this processing, which is capable of cleaving several prohormones at paired basic residues. The enzyme is a glycoprotein of Mr approximately 70,000 and has an acidic pH maximum. It processes the heterologous precursors pro-opiomelanocortin and insulin at paired basic residues in a manner similar to a pro-opiomelanocortin-converting enzyme derived from bovine intermediate lobe secretory vesicles which has been described previously. In addition, the neural lobe-derived converting enzyme cleaves the human vasopressin prohormone in vitro to yield arginine vasopressin-Gly10-Lys11-Arg12 as the major vasopressin cleavage product. This indicates that the enzymatic cleavage in the vasopressin precursor occurred primarily on the carboxyl side of the arginine in the pair of Lys-Arg basic residues separating the vasopressin peptide from the neurophysin moiety in the precursor. The properties of the neural and intermediate lobe-derived enzymes are virtually identical, raising the possibility that a family of similar enzymes may be responsible for cleaving a number of prohormones at paired basic residues in different tissues.     

In situ extraction versus the use of an external column in fermentation

Summary Organic extraction of 2,3-butanediol produced by Klebsiella oxytoca fermentation was studied to determine if the use of an external column offered advantages over in situ extractive fermentation. Dodecanol was chosen from 24 tested solvents, 11 of which were non-toxic to K. oxytoca. Although growth occurred in all shakeflask experiments containing dodecanol, growth was never observed when dodecanol was used in an in situ arrangement in a fermentor. Using dodecanol in an external column, however, resulted in a cell yield of 0.10 g/g d-xylose, and a 2,3-butanediol yield of 0.32 g/g d-xylose, similar to results obtained in control (solventless) experiments. Although the partitioning of 2,3-butanediol in the organic phase was low, this study suggests that external columns, with recycling to the fermentor, can offer substantial advantages over in situ extraction.     

Differential effects of estrogen on luteinizing hormone-releasing hormone gene expression in slice explant cultures prepared from specific rat forebrain regions

Five serially sectioned tissue slices (400 microns) from the preoptic area/hypothalamus of postnatal day 4 rats were cultured using a slice explant roller culture technique. After 18 days in culture, these slices thinned sufficiently to allow immunocytochemical and in situ hybridization histochemical assays for LHRH peptide and LHRH mRNA, respectively. Large numbers of neurons containing mRNA encoding LHRH were detected in these slices using in situ hybridization histochemistry (ISHH). These 35S-labeled cells were distributed in the cultured slices in a pattern similar to that found with LHRH immunocytochemistry and ISHH in vivo, indicating that LHRH neurons were maintained in these cultures in an organotypic manner. Densitometric single cell analyses after ISHH of the culture slices were performed using a Loats image analysis system, so as to provide a density value per cell (density/cell). Comparisons of these density values from the slice explants cultured in presence or absence of 10(-7) M estradiol found that: 1) under basal (control) culture conditions there were no consistent differences in the frequency distributions of the density/cell values between all the five slices derived from either male or female rats, 2) mean density/culture values under control conditions did not differ significantly between slices and sexes, 3) the presence of estradiol in the culture media resulted in an overall decrease in density/cell values, with the most significant decrease occurring in slice 3 which is comparable to the level of the organum vasculosum lamina terminalis/rostral preoptic area (OVLT/rPOA) in vivo, and 4) this decrease in density/cell values in slice 3 due to estradiol treatment, was greater in cultures derived from female vs. male tissues.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular Diversity in Neurosecretion: Reflections on the Hypothalamo-Neurohypophysial System

1. The diversity of molecules involved in various aspects of neurosecretion, such asproprotein processing, axonal transport of large dense core vesicles (LDCVs), and regulated secretion, is discussed in the context of the hypothalamo-neurohypophysial system (HNS).2. Recent studies have uncovered a family of at least seven processing enzymes known as proprotein convertases (PCs) which are involved in proteolytically cleaving protein precursors at paired basic amino acid motifs to yield biologically active peptides. Three of these, PC1(3), 2, and 5, are found in neurons and are involved in producing regulatedsecretory peptide products.3. The axonal transport of LDCVs occurs on microtubule tracks by still unknown mechanisms. There are over 11 distinct kinesin-related molecules that have now beenidentified as possible microtubule motor candidates.4. Calcium channels in the nervous system are known to be derived from at leastfive -subunit and four -subunit genes with multiple alternatively spliced isoforms in each case. These could account, in part, for the varied calcium currents found in the HNS.5. The large number of proteins and isoforms now demonstrated to be involved inregulated secretion are discussed, with a focus on LDCV compositions and the synaptotag-min gene family.     

Effect of dehydration on the endogenous opiate content of the art neuro-intermediate lobe

The relationship of endogenous opiate peptides of rat neuro-intermediate lobe to the release of neurohypophysial peptides has been investigated. Both dehydrated rats, with increased oxytocin and vasopressin release, as well as rats homozygous for hypothalamic diabetes insipidus (DI) of the Brattleboro strain, with increased oxytocin release, showed significantly decreased levels of pituitary opiate peptides. We suggest that neuro-intermediate lobe opiate peptides may modulate the release of neurohypophysial antidiuretic peptides.     

Onset of neurophysin self-association upon neurophysin/neuropeptide hormone precursor biosynthesis

32P-Labelled washed rabbit platelets were incubated with 0.6 nM platelet activating factor (PAF-acether), giving a full aggregation and release response within 30-60 s. The major phospholipid changes observed under these conditions were: (1) An increased labelling of phosphatidic acid (PA) within 10 s and of phosphatidylinositol (MPI) at 30 s, reflecting the activation of the MPI cycle via the cytosolic phospholipase C; (2) an enhancement of phosphatidylinositol-4-phosphate (DPI) and phosphatidylinositol-4,5-bisphosphate (TPI) labelling at later incubation times; (3) an early degradation of TPI with a counterbalancing formation of DPI. The latter changes suggest a receptor-mediated stimulation of TPI-phosphomonoesterase, the role of which in the mechanism of platelet activation is discussed.