Effects of adsorption to aluminum salt adjuvants on the structure and stability of model protein antigens

The effect of adsorption onto aluminum salt adjuvants on the structure and stability of three model protein antigens was studied using fluorescence and Fourier transform infrared spectroscopies, as well as isothermal titration and differential scanning calorimetric techniques. Lysozyme was preferentially adsorbed to aluminum phosphate (Adju-Phos), whereas ovalbumin and bovine serum albumin were better adsorbed to aluminum hydroxide (Alhydrogel). A linearized Langmuir adsorption isotherm was used to obtain information regarding the binding interactions between proteins and adjuvants. Binding energetics and stoichiometry data obtained from isothermal titration calorimetry measurements were complex. Based on the spectroscopic and differential scanning calorimetry studies, the structure of all three proteins, when adsorbed to the surface of an aluminum salt, was altered in such a way as to render the proteins less thermally stable. Besides the pharmaceutical significance of this destabilization, we consider the possibility that this phenomenon may facilitate the presentation of antigens and thus contribute to the adjuvant activity of the aluminum salts.     

Expressed Sequences from Conidial, Mycelial, and Sexual Stages ofNeurospora crassa

In theNeurosporaGenome Project at the University of New Mexico, expressed sequence tags (ESTs) corresponding to three stages of the life cycle of the filamentous fungusNeurospora crassaare being analyzed. The results of a pilot project to identify expressed genes and determine their patterns of expression are presented. 1,865 partial complementary DNA (cDNA) sequences for 1,409 clones were determined using single-pass sequencing. Contig analysis allowed the identification of 838 unique ESTs and 156 ESTs present in multiple cDNA clones. For about 34% of the sequences, highly or moderately significant matches to sequences (of known and unknown function) in the NCBI database were detected. Approximately 56% of the ESTs showed no similarity to previously identified genes. Among genes with assigned function, about 43.3% were involved in metabolism, 32.9% in protein synthesis and 8.4% in RNA synthesis. Fewer were involved in defense (6%), cell signalling (3.4%), cell structure (3.4%) and cell division (2.6%).     

Polyanions and the proteome

The behavior of the proteome reflects spatial and temporal organization both within and without cells. We propose that various macromolecular entities possessing polyanionic character such as proteoglycans, lipid bilayer surfaces, microtubules, microfilaments, and polynucleotides may provide a functional network that mediates a variety of cellular phenomena. The interaction of proteins with this array of polyanions is characterized by a lower degree of specificity than seen with most commonly recognized macromolecular interactions. In this commentary, potential roles for this polyanion network in diverse functions such as protein/protein interactions, protein folding and stabilization, macromolecular transport, and various disease processes are all considered, as well as the use of polyanions as therapeutic agents. The role of small polyanions in the regulation of protein/polyanion interactions is also postulated. We provide preliminary experimental analysis of the extent to which proteins interact with polyanions inside cells using a combination of two-dimensional chromatographic and electrophoretic methods and antibody arrays. We conclude that many hundreds to thousands of such interactions are present in cells and argue that future understanding of the proteome will require that the "polyanion world" be taken into account.     

Glucose deprivation stimulates O-GlcNAc modification of proteins through up-regulation of O-linked N-acetylglucosaminyltransferase

O-Linked N-acetylglucosamine (O-GlcNAc) is a post-translational modification of proteins that functions as a nutrient sensing mechanism. Here we report on regulation of O-GlcNAcylation over a broad range of glucose concentrations. We have discovered a significant induction of O-GlcNAc modification of a limited number of proteins under conditions of glucose deprivation. Beginning 12 h after treatment, glucose-deprived human hepatocellular carcinoma (HepG2) cells demonstrate a 7.8-fold increase in total O-GlcNAc modification compared with cells cultured in normal glucose (5 mm; p = 0.008). Some of the targets of glucose deprivation-induced O-GlcNAcylation are distinct from those modified in response to high glucose (20 mm) or glucosamine (10 mm) treatment, suggesting differential targeting with glucose deprivation and glucose excess. O-GlcNAcylation of glycogen synthase is significantly increased with glucose deprivation, and this O-GlcNAc increase contributes to a 60% decrease (p = 0.004) in glycogen synthase activity. Increased O-GlcNAc modification is not mediated by increased UDP-GlcNAc, the rate-limiting substrate for O-GlcNAcylation. Rather, the mRNA for nucleocytoplasmic O-linked N-acetylglucosaminyltransferase (OGT) increases 3.4-fold within 6 h of glucose deprivation (p = 0.006). Within 12 h, OGT protein increases 1.7-fold (p = 0.01) compared with normal glucose-treated cells. In addition, 12-h glucose deprivation leads to a 49% decrease in O-GlcNAcase protein levels (p = 0.03). We conclude that increased O-GlcNAc modification stimulated by glucose deprivation results from increased OGT and decreased O-GlcNAcase levels and that these changes affect cell metabolism, thus inactivating glycogen synthase.     

Ultrastructural damage in chromium picolinate-treated cells: a TEM study

Chromium picolinate (CrPic) is a human dietary supplement that provides a bioavailable form of chromium(III). Its mechanism of action is unknown, and a number of toxic endpoints have been attributed to its use. Understanding the cellular effects of CrPic is important for confirmation or dismissal of these potential toxic effects. The purpose of this work was to characterize morphological damage caused by CrPic, picolinic acid, and chromic chloride in Chinese hamster ovary AA8 cells. A 48-h exposure to 80 micro g/cm(2) CrPic (0.44 mg/mL CrPic) produced 45% survival by colony formation. Transmission electron microscopy (TEM) showed 83% of analyzed cells having swollen mitochondria with degraded cristae. Apoptosis was identified by nuclear convolution and fragmentation, and cytoplasmic blebbing. Apoptosis was quantified by fluorescence microscopy with acridine orange/ethidium bromide staining. At the 80 micro g/cm(2) dose of CrPic, 37% of the cells were apoptotic cells at 48 h. An equivalent dose of picolinate, 3 mM, was much more cytotoxic and thus there was an inadequate cell number for TEM analysis. However, a lower dose of 1.5 mM induced 49% cell survival, and damaged 86% of the mitochondria, with 51% of the cells undergoing apoptosis. A dose of 1 mM chromic chloride produced 71% cell survival, and damaged 86% of the mitochondria, with 22% of the cells undergoing apoptosis. The amount of apoptosis correlated with overall cell survival by colony formation, but not with the amount of mitochondrial damage. The coordination of Cr(III) by picolinate ligands may alter the cellular chemistry of Cr(III) to make chromium picolinate a toxic form of Cr(III).