Homology modelling of two subtilisin-like proteases from the hyperthermophilic archaea Pyrococcus furiosus and Thermococcus stetteri

The hyperthermophilic archaeon Pyrococcus furiosus produces an extracellular, glycosylated hyperthermostable subtilisin-like serine protease, termed pyrolysin (Voorhorst,W.G.B., Eggen,R.I.L., Geerling,A.C.M., Platteeuw,C., Siezen,R.J. and de Vos,W.M. (1996) J. Biol. Chem., 271, 20426-20431). Based on the pyrolysin coding sequence, a pyrolysin-like gene fragment was cloned and characterized from the extreme thermophilic archaeon Thermococcus stetteri. Like pyrolysin, the deduced sequence of this serine protease, designated stetterlysin, contains a catalytic domain with high homology with other subtilases, allowing homology modelling starting from known crystal structures. Comparison of the predicted three-dimensional models of the catalytic domain of stetterlysin and pyrolysin with the crystal structure of subtilases from mesophilic and thermophilic origin, i.e. subtilisin BPN' and thermitase, and the homology model of subtilisin S41 from psychrophilic origin, led to the identification of features that could be related to protein stabilization. Higher thermostability was found to be correlated with an increased number of residues involved in pairs and networks of charge-charge and aromatic-aromatic interactions. These highly thermostable proteases have several extra surface loops and inserts with a relatively high frequency of aromatic residues and Asn residues. The latter are often present in putative N-glycosylation sites. Results from modelling of known substrates in the substrate- binding region support the broad substrate range and the autocatalytic activation previously suggested for pyrolysin.      

Sila-haloperidol, a silicon analogue of the dopamine (D2) receptor antagonist haloperidol: synthesis, pharmacological properties, and metabolic fate

Haloperidol (1 a), a dopamine (D(2)) receptor antagonist, is in clinical use as an antipsychotic agent. Carbon/silicon exchange (sila-substitution) at the 4-position of the piperidine ring of 1 a (R(3)COH --> R(3)SiOH) leads to sila-haloperidol (1 b). Sila-haloperidol was synthesized in a new multistep synthesis, starting from tetramethoxysilane and taking advantage of the properties of the 2,4,6-trimethoxyphenyl unit as a unique protecting group for silicon. The pharmacological profiles of the C/Si analogues 1 a and 1 b were studied in competitive receptor binding assays at D(1)-D(5), sigma(1), and sigma(2) receptors. Sila-haloperidol (1 b) exhibits significantly different receptor subtype selectivities from haloperidol (1 a) at both receptor families. The C/Si analogues 1 a and 1 b were also studied for 1) their physicochemical properties (log D, pK(a), solubility in HBSS buffer (pH 7.4)), 2) their permeability in a human Caco-2 model, 3) their pharmacokinetic profiles in human and rat liver microsomes, and 4) their inhibition of the five major cytochrome P450 isoforms. In addition, the major in vitro metabolites of sila-haloperidol (1 b) in human liver microsomes were identified using mass-spectrometric techniques. Due to the special chemical properties of silicon, the metabolic fates of the C/Si analogues 1 a and 1 b are totally different.     

Pornography and Sexist Attitudes Among Heterosexuals

Using a probability‐based sample of young Danish adults and a randomized experimental design, this study investigated effects of past pornography consumption, experimental exposure to nonviolent pornography, perceived realism of pornography, and personality (i.e., agreeableness) on sexist attitudes (i.e., attitudes toward women, hostile and benevolent sexism). Further, sexual arousal mediation was assessed. Results showed that, among men, an increased past pornography consumption was significantly associated with less egalitarian attitudes toward women and more hostile sexism. Further, lower agreeableness was found to significantly predict higher sexist attitudes. Significant effects of experimental exposure to pornography were found for hostile sexism among low in agreeableness participants and for benevolent sexism among women. These experimental exposure effects were found to be mediated by sexual arousal.     

Reconstruction of graphs based on random walks

The analysis of complex networks is of major interest in various fields of science. In many applications we face the challenge that the exact topology of a network is unknown but we are instead given information about distances within this network. The theoretical approaches to this problem have so far been focusing on the reconstruction of graphs from shortest path distance matrices. Often, however, movements in networks do not follow shortest paths but occur in a random fashion. In these cases an appropriate distance measure can be defined as the mean length of a random walk between two nodes — a quantity known as the mean first hitting time.In this contribution we investigate whether a graph can be reconstructed from its mean first hitting time matrix and put forward an algorithm for solving this problem. A heuristic method to reduce the computational effort is described and analyzed. In the case of trees we can even give an algorithm for reconstructing graphs from incomplete random walk distance matrices.     

Blood-brain barrier carrier-mediated transport and brain metabolism of amino acids

We have examined the effects of the macrocyclic lactone protein kinase C (PKC) activator bryostatin 1 on taxol-induced apoptosis and inhibition of clonogenicity in the human monocytic leukemia cell line U937. Exposure of cells to bryostatin 1 (10 nM; 15 hr) after (but not before) a 6-hr incubation with 0.5 microM taxol significantly increased apoptosis and resulted in an approximately 3 log reduction in clonogenicity. Cell cycle analysis revealed that the increase in apoptotic cells following bryostatin 1 treatment occurred primarily in the population undergoing taxol-mediated G2M arrest. The actions of bryostatin 1 were not attributable to potentiation of taxol-induced tubulin stabilization or to a reduction in the intracellular retention of taxol. Following exposure of cells to taxol, the Bcl-2 protein displayed an alteration in mobility that was not modified appreciably by bryostatin 1 treatment. The mobility shift in Bcl-2 protein from cells exposed to taxol followed by bryostatin 1 was eliminated by treatment of lysates with the protein phosphatase 2A (PP2A); the latter effect was blocked by okadaic acid. Treatment of cells with taxol followed by bryostatin 1 did not increase the amount of total Bax (compared with treatment with taxol alone), but did increase the amount of free Bax in the supernatant fraction. Finally, the ability of bryostatin 1 to potentiate taxol-induced apoptosis in U937 cells was mimicked closely by 2'-amino-3'-methoxyflavone (PD98059), a specific inhibitor of the mitogen-activated protein kinase (MAPK) kinase (MEK). Collectively, these findings indicate that bryostatin 1 increases the susceptibility of U937 cells to taxol-induced apoptosis and inhibition of clonogenicity. They also raise the possibility that this phenomenon may involve functional alterations in Bcl-2 and/or other proteins involved in regulation of the cell death pathway.     

Analogues of the thrombin receptor tethered-ligand enhance mesangial cell proliferation

Thrombin stimulates cytosolic calcium mobilization and tritiated thymidine incorporation in rat glomerular mesangial cells. This effect may be mediated by a thrombin receptor similar to the receptor found in human platelets. In order to test this possibility, a series of analogues of the thrombin receptor peptide, SFLL-RNPNDKYEPF, was evaluated for their effects on mesangial cells. Analogues of the thrombin receptor peptide containing five, six, seven and 14 amino acids were as efficacious as thrombin with respect to calcium mobilization and thymidine incorporation, although they were significantly less potent. The dissimilarity in potency between thrombin and the thrombin receptor peptides is consistent with the kinetics of the proposed mechanism of action of the enzyme, since the cleavage by thrombin of its receptor results in a tethered ligand which is at a relatively high concentration compared to the free peptides in solution. Those thrombin receptor peptide analogues which showed decreased activity in platelets were tested in mesangial cells. Removal of serine at position one, N-acetylation, or replacement of the phenylalanine at position two with alanine resulted in analogues which were inactive in stimulating mesangial cell proliferation or calcium mobilization. In addition, those analogues which had no stimulatory effects in mesangial cells were not antagonists of SFLLRN-mediated calcium mobilization and thymidine incorporation in mesangial cells.     

The ultrastructure of an olfactory sensillum on the maxillary palps of locusta migratoria (L.)

The olfactory sensilla on the maxillary palp tip of Locusta migratoria (L.) resemble the surrounding contact chemoreceptors in general morphology. The perforated peg has a thicker wall than is commonly found in olfactory sensilla. The form and position of the sensilla are considered in relation of the olfactory function. The fine structure of the dendrites is discussed in relation to that described in other olfactory sensilla.