A vestige of a prebiotic bonding machine is functioning within the contemporary ribosome

Based on the presumed capability of a prebiotic pocket-like entity to accommodate substrates whose stereochemistry enables the creation of chemical bonds, it is suggested that a universal symmetrical region identified within all contemporary ribosomes originated from an entity that we term the 'proto-ribosome'. This 'proto-ribosome' could have evolved from an earlier machine that was capable of performing essential tasks in the RNA world, called here the 'pre-proto-ribosome', which was adapted for producing proteins.     

Robust control of nitrogen assimilation by a bifunctional enzyme in E. coli

Bacteria regulate the assimilation of multiple nutrients to enable growth. How is balanced utilization achieved, despite fluctuations in the concentrations of the enzymes that make up the regulatory circuitry? Here we address this question by studying the nitrogen system of E. coli. A mechanism based on the avidity of a bifunctional enzyme, adenylyltransferase (AT/AR), to its multimeric substrate, glutamine synthetase, is proposed to maintain a robust ratio between two key metabolites, glutamine and α-ketoglutarate. This ratio is predicted to be insensitive to variations in protein levels of the core circuit and to the rate of nitrogen utilization. We find using mass spectrometry that the metabolite ratio is robust to variations in protein levels and that this robustness depends on the bifunctional enzyme. Moreover, robustness carries through to the bacteria growth rate. Interrupting avidity by adding a monofunctional AT/AR mutant to the native system abolishes robustness, as predicted by the proposed mechanism.     

Whole-genome immunoinformatic analysis of F. tularensis: predicted CTL epitopes clustered in hotspots are prone to elicit a T-cell response

The cellular arm of the immune response plays a central role in the defense against intracellular pathogens, such as F. tularensis. To date, whole genome immunoinformatic analyses were limited either to relatively small genomes (e.g. viral) or to preselected subsets of proteins in complex pathogens. Here we present, for the first time, an unbiased bacterial global immunoinformatic screen of the 1740 proteins of F. tularensis subs. holarctica (LVS), aiming at identification of immunogenic peptides eliciting a CTL response. The very large number of predicted MHC class I binders (about 100,000, IC(50) of 1000 nM or less) required the design of a strategy for further down selection of CTL candidates. The approach developed focused on mapping clusters rich in overlapping predicted epitopes, and ranking these "hotspot" regions according to the density of putative binding epitopes. Limited by the experimental load, we selected to screen a library of 1240 putative MHC binders derived from 104 top-ranking highly dense clusters. Peptides were tested for their ability to stimulate IFNγ secretion from splenocytes isolated from LVS vaccinated C57BL/6 mice. The majority of the clusters contained one or more CTL responder peptides and altogether 127 novel epitopes were identified, of which 82 are non-redundant. Accordingly, the level of success in identification of positive CTL responders was 17-25 fold higher than that found for a randomly selected library of 500 predicted MHC binders (IC(50) of 500 nM or less). Most proteins (ca. 2/3) harboring the highly dense hotspots are membrane-associated. The approach for enrichment of true positive CTL epitopes described in this study, which allowed for over 50% increase in the dataset of known T-cell epitopes of F. tularensis, could be applied in immunoinformatic analyses of many other complex pathogen genomes.     

Modeling of human prokineticin receptors: interactions with novel small-molecule binders and potential off-target drugs

BACKGROUND AND MOTIVATION: The Prokineticin receptor (PKR) 1 and 2 subtypes are novel members of family A GPCRs, which exhibit an unusually high degree of sequence similarity. Prokineticins (PKs), their cognate ligands, are small secreted proteins of ～80 amino acids; however, non-peptidic low-molecular weight antagonists have also been identified. PKs and their receptors play important roles under various physiological conditions such as maintaining circadian rhythm and pain perception, as well as regulating angiogenesis and modulating immunity. Identifying binding sites for known antagonists and for additional potential binders will facilitate studying and regulating these novel receptors. Blocking PKRs may serve as a therapeutic tool for various diseases, including acute pain, inflammation and cancer. METHODS AND RESULTS: Ligand-based pharmacophore models were derived from known antagonists, and virtual screening performed on the DrugBank dataset identified potential human PKR (hPKR) ligands with novel scaffolds. Interestingly, these included several HIV protease inhibitors for which endothelial cell dysfunction is a documented side effect. Our results suggest that the side effects might be due to inhibition of the PKR signaling pathway. Docking of known binders to a 3D homology model of hPKR1 is in agreement with the well-established canonical TM-bundle binding site of family A GPCRs. Furthermore, the docking results highlight residues that may form specific contacts with the ligands. These contacts provide structural explanation for the importance of several chemical features that were obtained from the structure-activity analysis of known binders. With the exception of a single loop residue that might be perused in the future for obtaining subtype-specific regulation, the results suggest an identical TM-bundle binding site for hPKR1 and hPKR2. In addition, analysis of the intracellular regions highlights variable regions that may provide subtype specificity.     

Lineage-specific restraint of pituitary gonadotroph cell adenoma growth

Although pituitary adenomas are usually benign, unique trophic mechanisms restraining cell proliferation are unclear. As GH-secreting adenomas are associated with p53/p21-dependent senescence, we tested mechanisms constraining non-functioning pituitary adenoma growth. Thirty six gonadotroph-derived non-functioning pituitary adenomas all exhibited DNA damage, but undetectable p21 expression. However, these adenomas all expressed p16, and >90% abundantly expressed cytoplasmic clusterin associated with induction of the Cdk inhibitor p15 in 70% of gonadotroph and in 26% of somatotroph lineage adenomas (p = 0.006). Murine LβT2 and αT3 gonadotroph pituitary cells, and αGSU.PTTG transgenic mice with targeted gonadotroph cell adenomas also abundantly expressed clusterin and exhibited features of oncogene-induced senescence as evidenced by C/EBPβ and C/EBPδ induction. In turn, C/EBPs activated the clusterin promoter ～5 fold, and elevated clusterin subsequently elicited p15 and p16 expression, acting to arrest murine gonadotroph cell proliferation. In contrast, specific clusterin suppression by RNAis enhanced gonadotroph proliferation. FOXL2, a tissue-specific gonadotroph lineage factor, also induced the clusterin promoter ～3 fold in αT3 pituitary cells. As nine of 12 pituitary carcinomas were devoid of clusterin expression, this protein may limit proliferation of benign adenomatous pituitary cells. These results point to lineage-specific pathways restricting uncontrolled murine and human pituitary gonadotroph adenoma cell growth.     

Requirement of cognate CD4+ T-cell recognition for the regulation of allospecific CTL by human CD4+ CD127- CD25+ FOXP3+ cells generated in MLR

Although immunoregulation of alloreactive human CTLs has been described, the direct influence of CD4(+) Tregs on CD8(+) cytotoxicity and the interactive mechanisms have not been well clarified. Therefore, human CD4(+)CD127(-)CD25(+)FOXP3(+) Tregs were generated in MLR, immunoselected and their allospecific regulatory functions and associated mechanisms were then tested using modified (51)Chromium release assays (Micro-CML), MLRs and CFSE-based multi-fluorochrome flow cytometry proliferation assays. It was observed that increased numbers of CD4(+)CD127(-)CD25(+)FOXP3(+) cells were generated after a 7 day MLR. After immunoselection for CD4(+)CD127(-)CD25(+) cells, they were designated as MLR-Tregs. When added as third component modulators, MLR-Tregs inhibited the alloreactive proliferation of autologous PBMC in a concentration dependent manner. The inhibition was quasi-antigen specific, in that the inhibition was non-specific at higher MLR-Treg modulator doses, but non-specificity disappeared with lower numbers at which specific inhibition was still significant. When tested in micro-CML assays CTL inhibition occurred with PBMC and purified CD8(+) responders. However, antigen specificity of CTL inhibition was observed only with unpurified PBMC responders and not with purified CD8(+) responders or even with CD8(+) responders plus Non-T "APC". However, allospecificity of CTL regulation was restored when autologous purified CD4(+) T cells were added to the CD8(+) responders. Proliferation of CD8(+) cells was suppressed by MLR-Tregs in the presence or absence of IL-2. Inhibition by MLR-Tregs was mediated through down-regulation of intracellular perforin, granzyme B and membrane-bound CD25 molecules on the responding CD8(+) cells. Therefore, it was concluded that human CD4(+)CD127(-)CD25(+)FOXP3(+) MLR-Tregs down-regulate alloreactive cytotoxic responses. Regulatory allospecificity, however, requires the presence of cognate responding CD4(+) T cells. CD8(+) CTL regulatory mechanisms include impaired proliferation, reduced expression of cytolytic molecules and CD25(+) activation epitopes.     

High-nitrogen compost as a medium for organic container-grown crops

Compost was tested as a medium for organic container-grown crops. Nitrogen (N) loss during composting of separated cow manure (SCM) was minimized using high C/N (wheat straw, WS; grape marc, GM) or a slightly acidic (orange peels, OP) additives. N conservation values in the resultant composts were 82%, 95% and 98% for GM-SCM, OP-SCM and WS-SCM, respectively. Physical characteristics of the composts were compatible with use as growing media. The nutritional contribution of the composts was assessed using cherry tomato (Lycopersicon esculantum Mill.) and by means of incubation experiments. Media were either unfertilized or fertilized with guano (sea-bird manure). Plant responses suggest that N availability is the main variable affecting growth. Unfertilized OP-SCM and WS-SCM supplied the N needed for at least 4 months of plant growth. Root-galling index (GI) of tomato roots and number of eggs of the nematode Meloidogyne javanica were reduced by the composts, with the highest reduction obtained by OP-SCM and WS-SCM, at 50% concentrations. These composts, but not peat, reduced the incidence of crown and root-rot disease in tomato as well as the population size of the causal pathogen, Fusarium oxysporum f. sp. radicis-lycopersici.     

A novel protease from Entamoeba histolytica homologous to members of the family S28 of serine proteases

Serine proteases are one of the biologically most important and widely distributed enzyme families. A protease capable of degrading the substrate Suc-AAF-AMC was isolated from axenically grown trophozoites of Entamoeba histolytica. The enzyme was purified by ion-exchange chromatography and electroelution, and appeared on 2D-PAGE as a spot of 60 kDa and pI of 4.65. Data obtained from zymogram suggest the active protease is present either as homodimer (130 kDa) or homotetramer (250 kDa). The optimal temperature of the enzyme was 37 degrees C, and it exhibited activity over a broad pH range. The protease was strongly inhibited by TPCK and chelating agents. The enzymatic activity was restored upon addition of calcium. BLAST analysis with the sequence of internal peptides of the protein revealed two open reading frames within the genome of E. histolytica, homologous to members of the family S28, clan SC of serine proteases.     

Positively charged peptides can interact with each other, as revealed by solid phase binding assays

Solid phase assay systems such as enzyme-linked immunosorbent assay (ELISA), surface plasmon resonance (SPR), and overlay gels are used to study processes of protein-protein interactions. The common principle of all these methods is that they monitor the binding between soluble and surface-immobilized molecules. Following the use of bovine serum albumin (BSA)-peptide conjugates or isolated synthetic peptides and the above-mentioned solid phase assay systems, the results of the current work demonstrate that positively charged peptides can interact with each other. Both the ELISA and SPR methods demonstrated that the binding process reached saturation with K(d) values ranging between 1 and 14 nM. No interaction was observed between BSA conjugates bearing positively charged peptides and conjugates bearing negatively charged peptides or with pure BSA molecules, strengthening the view that interaction occurs only between positively charged peptides. However, interactions between peptides in solution were not observed by nuclear magnetic resonance (NMR) or by native gel electrophoresis. It appears that for positively charged molecules to interact, one of the binding partners must be immobilized to a surface, a process that may lead to the exposure of otherwise masked groups or atoms. We discuss the relevance of our findings for the use of solid phase assay systems to study interactions between biomolecules.