Bicyclic peptidomimetic tetrahydrofuro[3,2-b]pyrrol-3-one and hexahydrofuro[3,2-b]pyridine-3-one based scaffolds: synthesis and cysteinyl proteinase inhibition

A stereoselective synthesis of (3aS,6aR)-tetrahydrofuro[3,2-b]pyrrol-3-ones and (3aS,7aR)-hexahydrofuro[3,2-b]pyridine-3-ones has been developed through Fmoc protected scaffolds 12 and 13. A key design element within these novel bicyclic scaffolds, in particular the 5,5-fused system, was the inherent stability of the cis-fused geometry in comparison to that of the corresponding trans-fused. Since the bridgehead stereocentre situated beta to the ketone was of a fixed and stable configuration, the fact that cis ring fusion is both kinetically and thermodynamically stable with respect to trans ring fusion provides chiral stability to the bridgehead stereocentre that is situated alpha to the ketone. To exemplify this principle, building blocks 12 and 13 were designed, prepared and utilised in a solid phase combinatorial synthesis of peptidomimetic inhibitors 10, 45a-e, 11 and 46. Both series were chirally stable with 5,5-series 10 and 45a-e exhibiting potent in vitro activity against a range of CAC1 cysteinyl proteinases. Compound 10, a potent and selective inhibitor of cathepsin K, possessed good primary DMPK properties along with promising activity in an in vitro cell-based human osteoclast assay of bone resorption.     

A historical perspective of the glycosphingolipids and sphingolipidoses

Glycosphingolipids are a polysaccharide chain between 1 and 40 carbohydrate residues long glycosidically linked to ceramide (a long-chain aliphatic amino-alcohol or sphingoid) that is embedded in the cell plasma membrane with the carbohydrate moiety on the outside. The sphingoid imparts rigidity to the membrane and the carbohydrate tails protect the cell surface and have functions in relation to cell adhesion, growth, regulation, differentiation, cell interaction, recognition and signalling. They provide adhesion sites for pathogens and change during oncogenic transformation. Ceramide is also a component of sphingomyelin. Glycosphingolipids are degraded by lysosomal hydrolysis. The sphingolipidoses are a series of diseases in which mutations affecting the enzymes catalysing the last 11 steps of this process causing abnormal compounds proximal to the metabolic block to accumulate intralysosomally. Thus, they are a sub-group of the lysosomal storage diseases. The degradation of sphingolipids containing three or less carbohydrate residues requires a sphingolipid activator protein and mutations affecting these proteins also cause abnormal glycosphingolipid storage. With one exception (Fabry disease, which is X linked) the sphingolipidoses are inherited autosomally. The phenotypic manifestations of the individual sphingolipidoses are variable although the more severe variants are usually the better known. They have generally been regarded as untreatable but notable therapeutic advances are being made by enzyme replacement therapy and regulating the rate of glycosphingolipid synthesis by inhibiting UDP-glucose-N-acylsphingosine D-glucosyl transferase (CerGlcT), which is the first reaction on the pathway of glycosphingolipid synthesis. The compounds used are N-alkylated iminosugars whose glucose and galactose stereochemistries inhibit CerGlcT. Prenatal and carrier state diagnosis, genetic counselling and the abortion of affected foetuses are reducing the incidence of some of the most severe sphingolipidoses in certain high-incidence populations.     

Identification of novel ERK2 substrates through use of an engineered kinase and ATP analogs

The mitogen-activated protein kinases are key regulators of cellular organization and function. To understand the mechanisms(s) by which these ubiquitous kinases affect specific cellular changes, it is necessary to identify their diverse and numerous substrates in different cell contexts and compartments. As a first step in achieving this goal, we engineered a mutant ERK2 in which a bulky amino acid residue in the ATP binding site (glutamine 103) is changed to glycine, allowing this mutant to utilize an analog of ATP (cyclopentyl ATP) that cannot be used by wild-type ERK2 or other cellular kinases. The mutation did not inhibit ERK2 kinase activity or substrate specificity in vitro or in vivo. This method allowed us to detect only ERK2-specific phosphorylations within a mixture of proteins. Using this ERK2 mutant/analog pair to phosphorylate ERK2-associated proteins in COS-1 cells, we identified the ubiquitin ligase EDD (E3 identified by differential display) and the nucleoporin Tpr (translocated promoter region) as two novel substrates of ERK2, in addition to the known ERK2 substrate Rsk1. To further validate the method, we present data that confirm that ERK2 phosphorylates EDD in vitro and in vivo. These results not only identify two novel ERK2 substrates but also provide a framework for the future identification of numerous cellular targets of this important signaling cascade.     

Conformational similarities in the beta-ionone ring region of the rhodopsin chromophore in its ground state and after photoactivation to the metarhodopsin-I intermediate

High-resolution solid-state NMR methods have been used to analyze the conformation of the chromophore in the late photointermediate metarhodopsin-I, from observation of (13)C nuclei introduced into the beta-ionone ring (at the C16, C17, and C18 methyl groups) and into the adjoining segment of the polyene chain (at C8). Bovine rhodopsin in its native membrane was also regenerated with retinal that was (13)C-labeled close to the 11-Z bond (C20 methyl group) to provide a reporter for optimizing and quantifying the photoconversion to metarhodopsin-I. Indirect photoconversion via the primary intermediate, bathorhodopin, was adopted as the preferred method since approximately 44% conversion to the metarhodopsin-I component could be achieved, with only low levels (approximately 18%) of ground-state rhodopsin remaining. The additional photoproduct, isorhodopsin, was resolved in (13)C spectra from C8 in the chain, at levels of approximately 38%, and was shown using rotational resonance NMR to adopt the 6-s-cis conformation between the ring and the polyene chain. The C8 resonance was not shifted in the metarhodopsin-I spectral component but was strongly broadened, revealing that the local conformation had become less well defined in this segment of the chain. This line broadening slowed rotational resonance exchange with the C17 and C18 ring methyl groups but was accounted for to show that, despite the chain being more relaxed in metarhodopsin-I, its average conformation with respect to the ring was similar to that in the ground state protein. Conformational restraints are also retained for the C16 and C17 methyl groups on photoactivation, which, together with the largely preserved conformation in the chain, argues convincingly that the ring remains with strong contacts in its binding pocket prior to activation of the receptor. Previous conclusions based on photocrosslinking studies are considered in view of the current findings.     

Interfacial anchor properties of tryptophan residues in transmembrane peptides can dominate over hydrophobic matching effects in peptide-lipid interactions

Membrane model systems consisting of phosphatidylcholines and hydrophobic alpha-helical peptides with tryptophan flanking residues, a characteristic motif for transmembrane protein segments, were used to investigate the contribution of tryptophans to peptide-lipid interactions. Peptides of different lengths and with the flanking tryptophans at different positions in the sequence were incorporated in relatively thick or thin lipid bilayers. The organization of the systems was assessed by NMR methods and by hydrogen/deuterium exchange in combination with mass spectrometry. Previously, it was found that relatively short peptides induce nonlamellar phases and that relatively long analogues order the lipid acyl chains in response to peptide-bilayer mismatch. Here it is shown that these effects do not correlate with the total hydrophobic peptide length, but instead with the length of the stretch between the flanking tryptophan residues. The tryptophan indole ring was consistently found to be positioned near the lipid carbonyl moieties, regardless of the peptide-lipid combination, as indicated by magic angle spinning NMR measurements. These observations suggest that the lipid adaptations are not primarily directed to avoid a peptide-lipid hydrophobic mismatch, but instead to prevent displacement of the tryptophan side chains from the polar-apolar interface. In contrast, long lysine-flanked analogues fully associate with a bilayer without significant lipid adaptations, and hydrogen/deuterium exchange experiments indicate that this is achieved by simply exposing more (hydrophobic) residues to the lipid headgroup region. The results highlight the specific properties that are imposed on transmembrane protein segments by flanking tryptophan residues.     

Effects of the eukaryotic pore-forming cytolysin Equinatoxin II on lipid membranes and the role of sphingomyelin

Equinatoxin II (EqtII), a protein toxin from the sea anemone Actinia equina, readily creates pores in sphingomyelin-containing lipid membranes. The perturbation by EqtII of model lipid membranes composed of dimyristoylphosphatidycholine and sphingomyelin (10 mol %) was investigated using wideline phosphorus-31 and deuterium NMR. The preferential interaction between EqtII (0.1 and 0.4 mol %) and the individual bilayer lipids was studied by (31)P magic angle spinning NMR, and toxin-induced changes in bilayer morphology were examined by freeze-fracture electron microscopy. Both NMR and EM showed the formation of an additional lipid phase in sphingomyelin-containing mixed lipid multilamellar suspensions with 0.4 mol % EqtII. The new toxin-induced phase consisted of small unilamellar vesicles 20-40 nm in diameter. Deuterium NMR showed that the new lipid phase contains both dimyristoylphosphatidycholine and sphingomyelin. Solid-state (31)P NMR showed an increase in spin-lattice and a decrease in spin-spin relaxation times in mixed-lipid model membranes in the presence of EqtII, consistent with an increase in the intensity of low frequency motions. The (2)H and (31)P spectral intensity distributions confirmed a change in lipid mobility and showed the creation of an isotropic lipid phase, which was identified as the small vesicle structures visible by electron microscopy in the EqtII-lipid suspensions. The toxin appears to enhance slow motions in the membrane lipids and destabilize the membrane. This effect was greatly enhanced in sphingomyelin-containing mixed lipid membranes compared with pure phosphatidylcholine bilayers, suggesting a preferential interaction between the toxin and bilayer sphingomyelin.     

Detection and Phylogenetic Analysis of Novel Crenarchaeote and Euryarchaeote 16S Ribosomal RNA Gene Sequences from a Great Barrier Reef Sponge

The presence of Archaea in the Great Barrier Reef marine sponge Rhopaloeides odorabile was investigated by 16S ribosomal RNA community analysis of total DNA extracted from the sponge tissue. The 16S rRNA gene sequences corresponding to group I crenarchaeotes and group II euryarchaeotes were recovered from R. odorabile tissue. The location of archaeal cells within the sponge tissue was investigated using fluorescently labeled oligonucleotide probes. The presence of Archaea was confirmed within all regions of the sponge tissue from R. odorabile, with a significantly higher number of archaeal cells located in the pinacoderm than the mesohyl region. This is the first report of euryarchaeaotes associated with marine sponges. Received April 16, 2001; accepted June 27, 2001     

4-1BB ligand-mediated costimulation of human T cells induces CD4 and CD8 T cell expansion, cytokine production, and the development of cytolytic effector function

4-1BB (CD137) is a costimulatory member of the TNFR family expressed on activated T cells. Its ligand, 4-1BBL, is expressed on activated APC. In the mouse, CD8 T cells are preferentially activated by agonistic anti-murine 4-1BB Abs. However, murine 4-1BBL can stimulate both CD4 and CD8 T cells. To date, there are only limited data on the effects of 4-1BBL on human T cell responses. To further understand the role of 4-1BBL in human T cell responses, we compared human CD4 and CD8 T cell responses to transfected human 4-1BBL plus TCR-mediated stimulation. Both human CD4 and CD8 T cells responded to 4-1BBL. The presence of 4-1BBL on the APC led to increased expansion, cytokine production, and the development of cytolytic effector function by human T cells. In unfractionated T cell cultures, CD4 and CD8 T cells could expand to a similar extent in response to signals through the TCR and 4-1BB, as measured by CFSE labeling and by quantitating T cell numbers in the cultures. In contrast to the results with total T cells, isolated CD8 T cells produced less IL-2 and expanded to a lesser extent than isolated CD4 T cells responding to 4-1BBL. Thus, 4-1BBL is most effective when both CD4 and CD8 T cells are included in the cultures. CD28 and 4-1BB were found to synergize in the induction of IL-2 by human T cells, and CTLA-Ig partially blocked 4-1BBL-dependent IL-2 production. However, a portion of the 4-1BBL-mediated effects were independent of CD28-B7 interaction.     

New mutations of CIAS1 that are responsible for Muckle-Wells syndrome and familial cold urticaria: a novel mutation underlies both syndromes

Mutations of CIAS1 have recently been shown to underlie familial cold urticaria (FCU) and Muckle-Wells syndrome (MWS), in three families and one family, respectively. These rare autosomal dominant diseases are both characterized by recurrent inflammatory crises that start in childhood and that are generally associated with fever, arthralgia, and urticaria. The presence of sensorineural deafness that occurs later in life is characteristic of MWS. Amyloidosis of the amyloidosis-associated type is the main complication of MWS and is sometimes associated with FCU. In FCU, cold exposure is the triggering factor of the inflammatory crisis. We identified CIAS1 mutations, all located in exon 3, in nine unrelated families with MWS and in three unrelated families with FCU, originating from France, England, and Algeria. Five mutations--namely, R260W, D303N, T348M, A439T, and G569R--were novel. The R260W mutation was identified in two families with MWS and in two families with FCU, of different ethnic origins, thereby demonstrating that a single CIAS1 mutation may cause both syndromes. This result indicates that modifier genes are involved in determining either a MWS or a FCU phenotype. The finding of the G569R mutation in an asymptomatic individual further emphasizes the importance of such modifier a gene (or genes) in determining the disease phenotype. Identification of this gene (or these genes) is likely to have significant therapeutic implications for these severe diseases.