Mechanics of a mosquito bite with applications to microneedle design

The mechanics of a fascicle insertion into the skin by a mosquito of the type aedes aegypti has been studied experimentally using high-speed video (HSV) imaging, and analytically using a mathematical model. The fascicle is a polymeric microneedle composed of a ductile material, chitin. It has been proposed that the mosquito applies a non-conservative follower force component in addition to the Euler compressive load in order to prevent buckling and penetrate the skin. In addition, the protective sheath surrounding the fascicle (labium) provides lateral support during insertion. The mechanics model presented approximates the fascicle as a slender column supported on an elastic foundation (labium) subjected to non-conservative (Beck) and conservative Euler loads simultaneously at the end. Results show that the lateral support of the fascicle provided by the labium is essential for successful penetration by increasing the critical buckling load by a factor of 5. The non-conservative follower force application increases the buckling load by an additional 20% and may or may not be necessary for successful penetration. Experimental results showing the importance of the labium have been cited to validate the model predictions, in addition to the video observations presented in this work. This understanding may be useful in designing painless needle insertion systems as opposed to miniaturized hypodermic needles.

Differential recognition of phosphorylated transactivation domains of p53 by different p300 domains

Histone acetyltransferases form crucial links in transducing extrinsic signals to actual initiation of transcription. A multitude of stress signal integrations occur through the interaction of p300 with p53 phosphorylated at different residues of the transactivation domain. How such interactions activate different gene expression programs remains largely unknown. p300 contains at least five domains that are known to interact with p53, but their role in transcription regulation is not known. We measured the binding affinity of various phosphorylated transactivation domains towards several p53 binding domains of p300 by fluorescence anisotropy. The binding affinities of different phosphorylated transactivation domains of p53 towards different domains of p300 vary by several orders of magnitude, indicating that interactions of different post-translationally modified forms of p53 may occur through different domains of p300. Thus, different post-translationally modified p53 fragments may form transcription-initiating complexes of different configurations, leading to the activation of different promoters and pathways.

Specific inhibition of p300-HAT alters global gene expression and represses HIV replication

Reversible acetylation of histone and nonhistone proteins plays pivotal role in cellular homeostasis. Dysfunction of histone acetyltransferases (HATs) leads to several diseases including cancer, neurodegenaration, asthma, diabetes, AIDS, and cardiac hypertrophy. We describe the synthesis and characterization of a set of p300-HAT-specific small-molecule inhibitors from a natural nonspecific HAT inhibitor, garcinol, which is highly toxic to cells. We show that the specific inhibitor selectively represses the p300-mediated acetylation of p53 in vivo. Furthermore, inhibition of p300-HAT down regulates several genes but significantly a few important genes are also upregulated. Remarkably, these inhibitors were found to be nontoxic to T cells, inhibit histone acetylation of HIV infected cells, and consequently inhibit the multiplication of HIV.

Histone chaperones in chromatin dynamics: implications in disease manifestation

Histone chaperones are the histone interacting factors that stimulate histone transfer reaction without being a part of the final product. They are involved in the histone storage, histone translocation to the nucleus, and histone exchange and histone deposition onto the DNA for replication dependent chromatin assembly. Interestingly, they have also been demonstrated to possess the histone removal activity. While the involvement of the histone chaperones in chromatin transcription is undisputed, the question of their local versus global involvement is under scrutiny. This review enumerates the role played by various histone chaperones in the establishment of chromatin structure and regulation of chromatin transcription. The role of histone chaperones in disease manifestation is not very clear, preliminary results with few histone chaperones suggest that expression and function of these factors dramatically alters in carcinogenesis. This review will also focus on the possible role of histone chaperones in cancer diagnosis and progression

Small molecule modulators in epigenetics: implications in gene expression and therapeutics

Altered gene expression resulting from changes in the post-translational modification patterns of the histones and DNA is collectively termed epigenetics. Such changes are inherited albeit there are no alterations in the DNA sequence. Epigenetic regulation of gene expression is implemented by a wide repertoire of histone and DNA modifying enzymes including the acetyltransferases and deacetylases, the methyltransferases and kinases among others. Therefore, a regulation of these enzyme activities affords a tighter regulation of gene expression. Conversely, aberrant enzymatic activities lead to unregulated gene expression, resulting in several diseases such as RTS (loss of CBP HAT activity) and Spinal and Bulbar muscular atrophy (HATs and HMTases), apart from several forms of cancers, particularly myeloid leukemia (RAR-PML or RAR-PLZF fusion proteins resulting in the mistargeting of HDACs). Thus these enzymes have emerged as novel targets for the design of therapeutics. In this direction, several small molecule modulators (activators and inhibitors) of HATs, HDACs and HMTases are being reported in literature. This chapter introduces the different histone modifying enzymes involved in gene regulation, their connection to disease manifestation and focuses on the role of small molecule modulators in understanding enzyme function and also the design and the evolution of chromatin therapeutics

Human histone chaperone nucleophosmin enhances acetylation-dependent chromatin transcription

Histone chaperones are a group of proteins that aid in the dynamic chromatin organization during different cellular processes. Here, we report that the human histone chaperone nucleophosmin interacts with the core histones H3, H2B, and H4 but that this histone interaction is not sufficient to confer the chaperone activity. Significantly, nucleophosmin enhances the acetylation-dependent chromatin transcription and it becomes acetylated both in vitro and in vivo. Acetylation of nucleophosmin and the core histones was found to be essential for the enhancement of chromatin transcription. The acetylated NPM1 not only shows an increased affinity toward acetylated histones but also shows enhanced histone transfer ability. Presumably, nucleophosmin disrupts the nucleosomal structure in an acetylation-dependent manner, resulting in the transcriptional activation. These results establish nucleophosmin (NPM1) as a human histone chaperone that becomes acetylated, resulting in the enhancement of chromatin transcription.

Implications of small molecule activators and inhibitors of histone acetyltransferases in chromatin therapy

Histone acetylation is a diagnostic feature of transcriptionally active chromatin. The group of enzymes, histone acetyltransferases (HATs), involved in this crucial step of gene regulation, covalently modifies the N-terminal lysine residues of histones by the addition of an acetyl group from acetyl coenzyme A. Dysfunction of these enzymes is often associated with several diseases, ranging from neurodegenerative disorders to cancer. These enzymes thus are potential new targets for therapeutics. We have discovered few small molecule compounds, which target HATs and either activate or inhibit the enzyme potently. These compounds would be useful as biological switching molecules for probing into the role of HATs in gene regulation and cell cycle and may be useful as new chemical entities for the development of new drugs.

Polyisoprenylated benzophenone, garcinol, a natural histone acetyltransferase inhibitor, represses chromatin transcription and alters global gene expression

Histone acetylation is a diagnostic feature of transcriptionally active genes. The proper recruitment and function of histone acetyltransferases (HATs) and deacetylases (HDACs) are key regulatory steps for gene expression and cell cycle. Functional defects of either of these enzymes may lead to several diseases, including cancer. HATs and HDACs thus are potential therapeutic targets. Here we report that garcinol, a polyisoprenylated benzophenone derivative from Garcinia indica fruit rind, is a potent inhibitor of histone acetyltransferases p300 (IC50 approximately 7 microm) and PCAF (IC50 approximately 5 microm) both in vitro and in vivo. The kinetic analysis shows that it is a mixed type of inhibitor with an increased affinity for PCAF compared with p300. HAT activity-dependent chromatin transcription was strongly inhibited by garcinol, whereas transcription from DNA template was not affected. Furthermore, it was found to be a potent inducer of apoptosis, and it alters (predominantly down-regulates) the global gene expression in HeLa cells.

Small molecule modulators of histone acetyltransferase p300

Histone acetyltransferases (HATs) are a group of enzymes that play a significant role in the regulation of gene expression. These enzymes covalently modify the N-terminal lysine residues of histones by the addition of acetyl groups from acetyl-CoA. Dysfunction of these enzymes is often associated with the manifestation of several diseases, predominantly cancer. Here we report that anacardic acid from cashew nut shell liquid is a potent inhibitor of p300 and p300/CBP-associated factor histone acetyltranferase activities. Although it does not affect DNA transcription, HAT-dependent transcription from a chromatin template was strongly inhibited by anacardic acid. Furthermore, we describe the design and synthesis of an amide derivative N-(4-chloro-3-trifluoromethyl-phenyl)-2-ethoxy-6-pentadecyl-benzamide (CTPB) using anacardic acid as a synthon, which remarkably activates p300 HAT activity but not that of p300/CBP-associated factor. Although CTPB does not affect DNA transcription, it enhances the p300 HAT-dependent transcriptional activation from in vitro assembled chromatin template. However, it has no effect on histone deacetylase activity. These compounds would be useful as biological switching molecules for probing into the role of p300 in transcriptional studies and may also be useful as new chemical entities for the development of anticancer drugs.

Effect of phosphorylation on the structure and fold of transactivation domain of p53

Several phosphorylations are known to occur in the N-terminal transactivation domain of human p53. To explore the structural effects of these phosphorylations, we have chemically synthesized the unphosphorylated p53-(1-39) and its three phosphorylated analogs, phosphorylated at Ser-15, Thr-18, and Ser-20. p53-(1-39) and its Ser-15 and Thr-18 phosphorylated analogs were tested for interaction with p300. The order of binding affinities was similar to that derived from biochemical experiments with the whole protein, indicating functional integrity of the domain. Differences in chemical shifts and coupling constants indicate significant structural changes upon phosphorylations. The single tryptophan in the unphosphorylated domain has an emission maximum and a Stern-Volmer constant that are characteristics of tryptophans situated in protein interiors. The diffusion constant is monomer-like, with an axial ratio of 1:7.5, indicating a significant degree of compaction. Upon phosphorylations, the emission maximum and diffusion constant change significantly toward values that indicate more open conformations. Binding of the hydrophobic probe bis-1-anilino-8-naphthalenesulfonate to the unphosphorylated and one of the phosphorylated domains is also significantly different, suggesting different conformations. We propose that phosphorylations switch the largely folded transactivation domain to more open conformations that interact with transcription factors such as p300/cAMP- responsive element-binding protein-binding protein, leading to enhancement of gene expression.

An examination of the moisture sorption characteristics of commercial magnesium stearate

The objective of this study was to characterize the moisture sorption of magnesium stearate and the morphological changes, if any, resulting from moisture sorption. Six samples of commercial magnesium stearate USP were examined. Moisture sorption isotherms were obtained at 25 degrees C and 5% to 98% relative humidity (RH) using a moisture balance. Changes in crystal form resulting from moisture sorption were determined by x-ray diffraction. There were differences in the shape of the isotherm, reversibility of moisture uptake, and shape of the hysteresis loop in the isotherms of crystalline and amorphous magnesium stearates. The isotherm of crystalline magnesium stearate was almost parallel to the pressure axis until an RH of ~80% was reached, when there was desorption of practically all of the adsorbed water. The isotherm of the amorphous sample was characterized by continuous uptake of water over the entire range of RH. Exposure of amorphous magnesium stearate to RH greater than 70% resulted in the formation of the trihydrate. The trihydrate was converted into the anhydrous form when heated to a temperature of 100 degrees C to 105 degrees C. The trihydrate could be generated by exposing the anhydrate to RH higher than 70%.

p300-mediated acetylation of human transcriptional coactivator PC4 is inhibited by phosphorylation

The human positive coactivator 4 (PC4) acts as a general coactivator for activator-dependent transcription, the activity of which is regulated negatively by phosphorylation. We report here that PC4 can be acetylated specifically by another coactivator, p300. Interestingly, phosphorylation of PC4 by casein kinase II inhibits the p300-mediated acetylation. Mass spectral analysis revealed that there are at least two lysine residues acetylated in PC4, as a result of which its DNA binding activity is stimulated.

The effect of particle morphology on the physical stability of pharmaceutical powder mixtures: the effect of surface roughness of the carrier on the stability of ordered mixtures

The effect of particle morphology of the components on the physical stability of ordered mixtures was determined for a model system comprised of a mixture of micronized aspirin and a monodisperse carrier. Spray-dried lactose, crystallized lactose, microcrystalline cellulose, and dextrate were used as carriers. The surface texture of the carriers was quantified in terms of the ratio of the perimeter of the particles to that of an idealized shape at a constant magnification. Mixtures containing highly textured carriers segregated to a lesser extent than those containing smoother textured carriers. This was postulated to be due to the presence of a higher concentration of surface asperities on the coarse carriers that can constitute potentially strong adhesion sites for the fine component because of their higher energy relative to adjacent areas on the surface. The effect of the addition of a ternary component, magnesium stearate, on the stability of the above mixtures was studied. The observed differences in the segregation response were attributed to electrostatic charge effects.

Beta-globin gene haplotype in Hb SC disease

We asked the question, is the haplotype found with the sickle hemoglobin gene associated with different hematological characteristics in patients who were combined heterozygotes for sickle hemoglobin and hemoglobin C (Hb SC disease)? In 73 adults with Hb SC disease, a Benin haplotype chromosome was present in 56%, and Bantu (or Central African Republic; CAR), Senegal, and atypical haplotype chromosomes were found in 25%, 6%, and 12%, respectively. No significant difference were found in hematological characteristics or fetal hemoglobin levels of patients with Benin/C, CAR/C, Senegal/C, and atypical/C haplotypes. There were 71% C I, 18% C II, and 11% other beta(c) haplotypes. Fetal hemoglobin levels are lower in Hb SC disease than in sickle-cell anemia. Perhaps because haplotype has no discernible effect on fetal hemoglobin level in Hb SC disease, it does not modulate its hematological features.

Crystal and molecular structure of the antibiotic blasticidin S hydrochloride pentahydrate

The three-dimensional structure of blasticidin S hydrochloride pentahydrate, a member of the cytosine amino nucleoside antibiotics, has been solved using diffractometer data and refined to an R value of 0.115. The crystal data are a = 13.500(5), b = 20.387(7), c = 4.824 A, beta = 98.66(3) degrees, Z = 2, Dc = 1.389 g .cm-3, space group P21. The nucleoside base conformation is anti(chi = 86 degrees) and the 2',3'-unsaturated pyranosyl sugar exhibits a half-chair (degree H5) conformation. The amide plane is twisted from the trans position by about 10 degrees. The guanidium group and the amino group of the amino acid chain are positively charged, while the carboxyl group of the sugar is ionized. The chloride ion is surrounded by water molecules only, in a trigonal prismatic arrangement. The molecule has an extended conformation and there is an intramolecular hydrogen bond between the ammonium group and the carboxyl group. A striking feature of blasticidin is that all the hydrophilic groups lie on one side of the molecule and the hydrophobic groups on the other. Amicetin also shows a similar feature and this might be linked to the commonality of their antibiotic functions. Hydrogen bonds link the hydrophilic sides of adjacent molecules forming double chains parallel to the b-axis. The hydrophobic sides of adjacent double chains are separated by a water layer.