Immune response of horses to vaccination with the recombinant Hc domain of botulinum neurotoxin types C and D

Botulinum neurotoxins, predominantly serotypes C and D, cause equine botulism through forage poisoning. The C-terminal part of the heavy chain of botulinum neurotoxin types C and D (HcBoNT/C and D) was expressed in Escherichia coli and evaluated as a recombinant mono- and bivalent vaccine in twelve horses in comparison to a commercially available toxoid vaccine. A three-dose subcutaneous immunization of adult horses elicited robust serum antibody response in an ELISA using the immunogen as a capture antigen. Immune sera showed dose-dependent high potency in neutralizing specifically the active BoNT/C and D in the mouse protection assay. The aluminium hydroxide based mono- and bivalent recombinant HcBoNT/C and D vaccines were characterized by good compatibility and the ability to elicit protective antibody titers similar or superior to the commercially available toxoid vaccine.

Quantification of global DNA methylation with infrared fluorescence in liver and muscle tissues of differentially fed boars

Methylation of cytosine residues at CpG sites is involved in various biological processes to control gene regulation and gene expression. Global DNA methylation is changed in different tumors and in cloned animals. Global DNA methylation can be accurately quantified by dot blot analysis with infrared (IR) fluorophores. Methylated lambda DNA was used as model DNA to develop and validate an immunochemical assay with IR fluorescence detection. Two different IR fluorophores were used, one to detect 5-methylcytosine and another to account for DNA loading. A sensitive infrared detection method was established which is suitable for accurate and reproducible quantification of global DNA methylation across a wide dynamic range. This method was subsequently employed to quantify global DNA methylation in liver and in muscle tissues of boars which have received either a control diet or a methyl supplemented diet in an ongoing study. A significant difference in global DNA methylation is indicated in muscle but not in liver tissue between the two groups of boars.

The Bcl-2 Protein Family Member Bok Binds to the Coupling Domain of Inositol 1,4,5-Trisphosphate Receptors and Protects Them from Proteolytic Cleavage

Bok is a member of the Bcl-2 protein family that controls intrinsic apoptosis. Bok is most closely related to the pro-apoptotic proteins Bak and Bax, but in contrast to Bak and Bax, very little is known about its cellular role. Here we report that Bok binds strongly and constitutively to inositol 1,4,5-trisphosphate receptors (IP3Rs), proteins that form tetrameric calcium channels in the endoplasmic reticulum (ER) membrane and govern the release of ER calcium stores. Bok binds most strongly to IP3R1 and IP3R2, and barely to IP3R3, and essentially all cellular Bok is IP3R bound in cells that express substantial amounts of IP3Rs. Binding to IP3Rs appears to be mediated by the putative BH4 domain of Bok and the docking site localizes to a small region within the coupling domain of IP3Rs (amino acids 1895–1903 of IP3R1) that is adjacent to numerous regulatory sites, including sites for proteolysis. With regard to the possible role of Bok-IP3R binding, the following was observed: (i) Bok does not appear to control the ability of IP3Rs to release ER calcium stores, (ii) Bok regulates IP3R expression, (iii) persistent activation of inositol 1,4,5-trisphosphate-dependent cell signaling causes Bok degradation by the ubiquitin-proteasome pathway, in a manner that parallels IP3R degradation, and (iv) Bok protects IP3Rs from proteolysis, either by chymotrypsin in vitro or by caspase-3 in vivo during apoptosis. Overall, these data show that Bok binds strongly and constitutively to IP3Rs and that the most significant consequence of this binding appears to be protection of IP3Rs from proteolysis. Thus, Bok may govern IP3R cleavage and activity during apoptosis.

Gas-phase Dissociation of homo-DNA Oligonucleotides

Synthetic modified oligonucleotides are of interest for diagnostic and therapeutic applications, as their biological stability, pairing selectivity, and binding strength can be considerably increased by the incorporation of unnatural structural elements. Homo-DNA is an oligonucleotide homologue based on dideoxy-hexopyranosyl sugar moieties, which follows the Watson-Crick A-T and G-C base pairing system, but does not hybridize with complementary natural DNA and RNA. Homo-DNA has found application as a bioorthogonal element in templated chemistry applications. The gas-phase dissociation of homo-DNA has been investigated by ESI-MS/MS and MALDI-MS/MS, and mechanistic aspects of its gas-phase dissociation are discussed. Experiments revealed a charge state dependent preference for the loss of nucleobases, which are released either as neutrals or as anions. In contrast to DNA, nucleobase loss from homo-DNA was found to be decoupled from backbone cleavage, thus resulting in stable products. This renders an additional stage of ion activation necessary in order to generate sequence-defining fragment ions. Upon MS(3) of the primary base-loss ion, homo-DNA was found to exhibit unspecific backbone dissociation resulting in a balanced distribution of all fragment ion series.

Hypoxia refines plasticity of mitochondrial respiration to repeated muscle work.

PURPOSE We explored whether altered expression of factors tuning mitochondrial metabolism contributes to muscular adaptations with endurance training in the condition of lowered ambient oxygen concentration (hypoxia) and whether these adaptations relate to oxygen transfer as reflected by subsarcolemmal mitochondria and oxygen metabolism in muscle. METHODS Male volunteers completed 30 bicycle exercise sessions in normoxia or normobaric hypoxia (4,000 m above sea level) at 65% of the respective peak aerobic power output. Myoglobin content, basal oxygen consumption, and re-oxygenation rates upon reperfusion after 8 min of arterial occlusion were measured in vastus muscles by magnetic resonance spectroscopy. Biopsies from vastus lateralis muscle, collected pre and post a single exercise bout, and training, were assessed for levels of transcripts and proteins being associated with mitochondrial metabolism. RESULTS Hypoxia specifically lowered the training-induced expression of markers of respiratory complex II and IV (i.e. SDHA and isoform 1 of COX-4; COX4I1) and preserved fibre cross-sectional area. Concomitantly, trends (p < 0.10) were found for a hypoxia-specific reduction in the basal oxygen consumption rate, and improvements in oxygen repletion, and aerobic performance in hypoxia. Repeated exercise in hypoxia promoted the biogenesis of subsarcolemmal mitochondria and this was co-related to expression of isoform 2 of COX-4 with higher oxygen affinity after single exercise, de-oxygenation time and myoglobin content (r ≥ 0.75). Conversely, expression in COX4I1 with training correlated negatively with changes of subsarcolemmal mitochondria (r < -0.82). CONCLUSION Hypoxia-modulated adjustments of aerobic performance with repeated muscle work are reflected by expressional adaptations within the respiratory chain and modified muscle oxygen metabolism.

AMPA RECEPTOR ALLOSTERISM: MEASUREMENT OF THE CONFORMATIONAL CHANGES IN THE LIGAND BINDING DOMAIN OF A FUNCTIONAL RECEPTOR

Ionotropic glutamate receptors are important excitatory neurotransmitter receptors in the mammalian central nervous system that have been implicated in a number of neuropathologies such as epilepsy, ischemia, and amyotrophic lateral sclerosis. Glutamate binding to an extracellular ligand binding domain initiates a series of structural changes that leads to the formation of a cation selective transmembrane channel, which consequently closes due to desensitization of the receptor. The crystal structures of the AMPA subtype of the glutamate receptor have been particularly useful in providing initial insight into the conformational changes in the ligand binding domain; however, these structures are limited by crystallographic constraint. To gain a clear picture of how agonist binding is coupled to channel activation and desensitization, it is essential to study changes in the ligand binding domain in a dynamic, physiological state. In this dissertation, a technique called Luminescence Resonance Energy Transfer was used to determine the conformational changes associated with activation and desensitization in a functional AMPA receptor (ÄN*-AMPA) that contains the ligand binding domain and transmembrane segments; ÄN*-AMPA has been modified such that fluorophores can be introduced at specific sites to serve as a readout of cleft closure or to establish intersubunit distances. Previous structural studies of cleft closure of the isolated ligand binding domain in conjunction with functional studies of the full receptor suggest that extent of cleft closure correlates with extent of activation. Here, LRET has been used to show that a similar relationship between cleft closure and activation is observed in the “full length” receptor showing that the isolated ligand binding domain is a good model of the domain in the full length receptor for changes within a subunit. Similar LRET investigations were used to study intersubunit distances specifically to probe conformational changes between subunits within a dimer in the tetrameric receptor. These studies show that the dimer interface is coupled in the open state, and decoupled in the desensitized state, similar to the isolated ligand binding domain crystal structure studies. However, we show that the apo state dimer interface is not pre-formed as in the crystal structure, hence suggesting a mechanism for functional transitions within the receptor based on LRET distances obtained.

Polymorphisms of the DNA repair gene MGMT and risk and progression of head and neck cancer.

Methylating agents are involved in carcinogenesis, and the DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT) removes methyl group from O(6)-methylguanine. Genetic variation in DNA repair genes has been shown to contribute to susceptibility to squamous cell carcinoma of the head and neck (SCCHN). We hypothesize that MGMT polymorphisms are associated with risk of SCCHN. In a hospital-based case-control study of 721 patients with SCCHN and 1234 cancer-free controls frequency-matched by age, sex and ethnicity, we genotyped four MGMT polymorphisms, two in exon 3, 16195C>T and 16286C>T and two in the promoter region, 45996G>T and 46346C>A. We found that none of these polymorphisms alone had a significant effect on risk of SCCHN. However, when these four polymorphisms were evaluated together by the number of putative risk genotypes (i.e. 16195CC, 16286CC, 45996GT+TT, and 46346CA+AA), a statistically significantly increased risk of SCCHN was associated with the combined genotypes with three to four risk genotypes, compared with those with zero to two risk genotypes (adjusted odds ratio (OR)=1.27; 95% confidence interval (CI)=1.05-1.53). This increased risk was also more pronounced among young subjects (OR=1.81; 95% CI=1.11-2.96), men (OR=1.24; 95% CI=1.00-1.55), ever smokers (OR=1.25; 95%=1.01-1.56), ever drinkers (OR=1.29; 95% CI=1.04-1.60), patients with oropharyngeal cancer (OR=1.45; 95% CI=1.12-1.87), and oropharyngeal cancer with regional lymph node metastasis (OR=1.52; 95% CI=1.16-1.89). In conclusion, our results suggest that any one of MGMT variants may not have a substantial effect on SCCHN risk, but a joint effect of several MGMT variants may contribute to risk and progression of SCCHN, particularly for oropharyngeal cancer, in non-Hispanic whites.

The C-terminal domain of MinC inhibits assembly of the Z ring in Escherichia coli.

In Escherichia coli, the Min system, consisting of three proteins, MinC, MinD, and MinE, negatively regulates FtsZ assembly at the cell poles, helping to ensure that the Z ring will assemble only at midcell. Of the three Min proteins, MinC is sufficient to inhibit Z-ring assembly. By binding to MinD, which is mostly localized at the membrane near the cell poles, MinC is sequestered away from the cell midpoint, increasing the probability of Z-ring assembly there. Previously, it has been shown that the two halves of MinC have two distinct functions. The N-terminal half is sufficient for inhibition of FtsZ assembly, whereas the C-terminal half of the protein is required for binding to MinD as well as to a component of the division septum. In this study, we discovered that overproduction of the C-terminal half of MinC (MinC(122-231)) could also inhibit cell division and that this inhibition was at the level of Z-ring disassembly and dependent on MinD. We also found that fusing green fluorescent protein to either the N-terminal end of MinC(122-231), the C terminus of full-length MinC, or the C terminus of MinC(122-231) perturbed MinC function, which may explain why cell division inhibition by MinC(122-231) was not detected previously. These results suggest that the C-terminal half of MinC has an additional function in the regulation of Z-ring assembly.

CONFORMATIONAL CHANGES IN THE EXTRACELLULAR DOMAIN OF GLUTAMATE RECEPTORS

The family of membrane protein called glutamate receptors play an important role in the central nervous system in mediating signaling between neurons. Glutamate receptors are involved in the elaborate game that nerve cells play with each other in order to control movement, memory, and learning. Neurons achieve this communication by rapidly converting electrical signals into chemical signals and then converting them back into electrical signals. To propagate an electrical impulse, neurons in the brain launch bursts of neurotransmitter molecules like glutamate at the junction between neurons, called the synapse. Glutamate receptors are found lodged in the membranes of the post-synaptic neuron. They receive the burst of neurotransmitters and respond by fielding the neurotransmitters and opening ion channels. Glutamate receptors have been implicated in a number of neuropathologies like ischemia, stroke and amyotrophic lateral sclerosis. Specifically, the NMDA subtype of glutamate receptors has been linked to the onset of Alzheimer’s disease and the subsequent degeneration of neuronal cells. While crystal structures of AMPA and kainate subtypes of glutamate receptors have provided valuable information regarding the assembly and mechanism of activation; little is known about the NMDA receptors. Even the basic question of receptor assembly still remains unanswered. Therefore, to gain a clear understanding of how the receptors are assembled and how agonist binding gets translated to channel opening, I have used a technique called Luminescence Resonance Energy Transfer (LRET). LRET offers the unique advantage of tracking large scale conformational changes associated with receptor activation and desensitization. In this dissertation, LRET, in combination with biochemical and electrophysiological studies, were performed on the NMDA receptors to draw a correlation between structure and function. NMDA receptor subtypes GluN1 and GluN2A were modified such that fluorophores could be introduced at specific sites to determine their pattern of assembly. The results indicated that the GluN1 subunits assembled across each other in a diagonal manner to form a functional receptor. Once the subunit arrangement was established, this was used as a model to further examine the mechanism of activation in this subtype of glutamate receptor. Using LRET, the correlation between cleft closure and activation was tested for both the GluN1 and GluN2A subunit of the NMDA receptor in response to agonists of varying efficacies. These investigations revealed that cleft closure plays a major role in the mechanism of activation in the NMDA receptor, similar to the AMPA and kainate subtypes. Therefore, suggesting that the mechanism of activation is conserved across the different subtypes of glutamate receptors.

Structural studies of cytochrome P4501A1: Identification of substrate and cumene hydroperoxide binding regions in the active site of P4501A1 and characterization of the P4501A1 interaction with cytochrome P450 reductase

Cytochromes P450 are a superfamily of heme-thiolate proteins that function in a concert with another protein, cytochrome P450 reductase, as terminal oxidases of an enzymatic system catalyzing the metabolism of a variety of foreign compounds and endogenous substrates. In order to better understand P450s catalytic mechanism and substrate specificity, information about the structure of the active site is necessary. Given the lack of a crystal structure of mammalian P450, other methods have been used to elucidate the substrate recognition and binding site structure in the active center. In this project I utilized the photoaffinity labeling technique and site-directed mutagenesis approach to gain further structural insight into the active site of mammalian cytochrome P4501AI and examine the role of surface residues in the interaction of P4501A1 with the reductase. ^ Four crosslinked peptides were identified by photoaffinity labeling using diazido benzphetamine as a substrate analog. Alignment of the primary structure of cytochrome P4501A1 with that of bacterial cytochrome P450102 (the crystal structure of which is known) revealed that two of the isolated crosslinked peptides can be placed in the vicinity of heme (in the L helix region and β10-β11 sheet region of cytochrome P450102) and could be involved in substrate binding. The other two peptides were located on the surface of the protein with the label bound specifically to Lys residues that were proposed to be involved in reductase-P450 interaction. ^ Alternatively, it has been shown that some of the organic hydroperoxides can support P450 catalyzed reactions in the absence of NADPH, O2 and reductase. By means of photoaffinity labeling the cumene hydroperoxide binding region was identified. Using azidocumene as the photoaffinity label, the tripeptide T501-L502-K503 was shown to be the site where azidocumene covalently binds to P4501A1. The sequence alignment of cytochrome P4501A1 with cytochrome P450102 predicts that this region might correspond to β-sheet structure localized on the distal side of the heme ring near the I helix and the oxygen binding pocket. The role of Thr501 in the cumene hydroperoxide binding was confirmed by mutations of this residue and kinetic analysis of the effects of the mutations. ^ In addition, the role of two lysine residues, Lys271 and Lys279, in the interaction with reductase was examined by means of site-directed mutagenesis. The lysine residues were substituted with isoleucine and enzymatic activity of the wild type and the mutants were compared in reductase- and cumene hydroperoxide-supported systems. The lysine 279 residue has been shown to play a critical role in the P4501A1-reductase interaction. ^

AN ANALYSIS OF THE DNA DAMAGE INDUCED BY NICKEL COMPOUNDS IN CHINESE HAMSTER OVARY CELLS (CARCINOGENESIS, HETEROCHROMATIN, CYTOTOXICITY, REPLICATION, PROTEIN CROSSLINKING)

The carcinogenic activity of water-insoluble crystalline nickel sulfide requires phagocytosis and lysosome-mediated intracellular dissolution of the particles to yield Ni('2+). This study investigated the extent and nature of the DNA damage in Chinese hamster ovary cells treated with various nickel compounds using the technique of alkaline elution. Crystalline NiS and water-soluble NiCl(,2) induced single strand breaks that were repaired quickly and DNA-protein crosslinks that persisted up to 24 hr after exposure to nickel. The induction of single strand breaks was concentration dependent at both noncytotoxic and lethal amounts of nickel. The induction of DNA-protein crosslinks was concentration dependent but was absent at lethal amounts of nickel. The cytoplasmic and nuclear uptake of nickel was concentration dependent even at the toxic level of nickel. However, the induction of DNA-protein crosslinks by nickel required active cell cycling and occurred predominantly in mid-late S phase of the cell cycle, suggesting that the lethal amounts of nickel inhibited DNA-protein crosslinking by inhibiting active cell cycling. Since the DNA-protein crosslinking induced by nickel was resistant to DNA repair, the nature of this lesion was investigated using various methods of DNA isolation and chromatin fractionation in combination with SDS-polyacrylamide gel electrophoresis. High molecular weight, non-histone chromosomal proteins and possibly histone 1 were preferentially crosslinked to DNA by nickel. The crosslinked proteins were concentrated in a magnesium-insoluble fraction of sonicated chromatin (5% of the total) that was similar to heterochromatin in solubility and protein composition. Alterations in DNA structure and function, brought about by the effect of nickel on protein-DNA interactions, may be related to the carcinogenicity of nickel compounds. ^

CHROMOSOMAL ORIGIN OF DM-DNA

Double minutes (dm) are small chromatin particles of 0.3 microns diameter found only in the metaphase cells of human and murine tumors. Dm are unique cytogenetic structures since their numbers per cell show wide variation. At cell division, dm are retained despite the lack of centromeres. In squash preparations, dm show clustering often in association with chromosomes. Human carcinoma cell line SW613-S18 was found to have large numbers of dm and biological characteristics favorable for mitotic synchronization and chromosome isolation experiments.^ S18 cells were synchronized to mitosis with metabolic and mitotic blocking compounds. Mitotic cells were lysed to release chromosomes and dm from the mitotic spindle and the resulting suspensions were fractionated to enrich for dm. The DNA in enriched fractions was characterized. The reassociation kinetics of dm-DNA driven with placental human DNA was similar to the reassociation curve of labeled placental DNA under similar conditions. In situ hybridization of dm-DNA to tumor and normal metaphase cells showed grain localization over the entire karyotype. Dm-DNA was shown by pulse chase DNA replication experiments to replicate during early and mid S-phase of the cell cycle, but not in late S-phase. In addition, BrdUrd incorporation studies showed that dm-DNA replicates only once during the S-phase. Premature chromosome condensation studies suggest the basis of numerical heterogeneity of dm is nondisjunction, not anomalous or unscheduled DNA replication.^ These data and previous cytochemical banding studies of dm in SW613-S18 indicate that dm-DNA is chromosomal in origin. No evidence of gene amplification was found in the DNA reassociation data. It is likely that dm-DNA represents the pale-staining G-band regions of the human karyotype in this cell line. ^