Enzyme precipitate coatings of lipase on polymer nanofibers

Lipase (LP) was immobilized on electrospun and ethanol-dispersed polystyrene–poly(styrene-co-maleic anhydride) (PS–PSMA) nanofibers (EtOH-NF) in the form of enzyme precipitate coatings (EPCs). LP precipitate coatings (EPCs-LP) were prepared in a three-step process, consisting of covalent attachment, LP precipitation, and crosslinking of precipitated LPs onto the covalently attached LPs via glutaraldehyde treatment. The LP precipitation was performed by adding various concentrations of ammonium sulfate (20–50%, w/v). EPCs-LP improved the LP activity and stability when compared to covalently attached LPs (CA-LP) and the enzyme coatings of LPs (EC-LP) without the LP precipitation. For example, the use of 40% (w/v) ammonium sulfate resulted in EPC40-LP with the highest activity, which was 4.0 and 3.6 times higher than those of CA-LP and EC-LP, respectively. After 165-day incubation under rigorous shaking at 200 rpm, the residual activities of EPC50-LP were 0.5 μM/min mg of EtOH-NF, representing 113 and 75 times higher than those of CA-LP and EC-LP, respectively. When LP was partially purified via a simple ammonium sulfate precipitation and dialysis, both activities and stabilities of EC-LP and EPC-LP could be marginally improved. It is anticipated that the improved LP activity and stability in the form of EPCs would allow for their potential applications in various bioconversion processes such as biodiesel production and ibuprofen resolution.     

Selective tumor targeting by enhanced permeability and retention effect. Synthesis and antitumor activity of polyphosphazene-platinum (II) conjugates

Nanosized polyphosphazene-platinum (II) conjugates with a wide range of molecular weight from 24,000 to 115,000 were synthesized to study their tumor selectivity by enhanced permeability and retention (EPR) effect and their antitumor activity. It has been found from biodistribution study that the present polyphosphazene-Pt(II) conjugates exhibit high tumor selectivity by EPR effect with the tumor to tissue ratio (TTR) from 3.6 to 13 depending on the molecular size. These polymer conjugates have shown excellent in vivo antitumor activity against both murine and human cancer cell lines. In particular, xenograft trials of the conjugates have shown outstanding tumor inhibition effect on the stomach cancer cell line, YCC-3, which is one of the least responsive to the anticancer agents currently in clinical use, although the reason is not clearly explainable yet. The high in vivo activity seems to be attributed to the controlled-release of the antitumor active platinum (II) moiety, [GlyGluPt(dach] (dach=trans-(+/-)-1,2-diaminocyclohexane) from the phosphazene backbone by degradation in aqueous solution.     

Synthesis, characterization, and pharmacokinetic studies of PEGylated glucagon-like peptide-1

Glucagon-like peptide-1-(7-36) (GLP-1) is a hormone derived from the proglucagon molecule, which is considered a highly desirable antidiabetic agent mainly due to its unique glucose-dependent stimulation of insulin secretion profiles. However, the development of a GLP-1-based pharmaceutical agent has a severe limitation due to its very short half-life in plasma, being primarily degraded by dipeptidyl peptidase IV (DPP-IV) enzyme. To overcome this limitation, in this article we propose a novel and potent DPP-IV-resistant form of a poly(ethylene glycol)-conjugated GLP-1 preparation and its pharmacokinetic evaluation in rats. Two series of mono-PEGylated GLP-1, (i) N-terminally modified PEG(2k)-N(ter)-GLP-1 and (ii) isomers of Lys(26), Lys(34) modified PEG(2k)-Lys-GLP-1, were prepared by using mPEG-aldehyde and mPEG-succinimidyl propionate, respectively. To determine the optimized condition for PEGylation, the reactions were monitored at different pH buffer and time intervals by RP-HPLC and MALDI-TOF-MS. The in vitro insulinotropic effect of PEG(2k)-Lys-GLP-1 showed comparable biological activity with native GLP-1 (P = 0.11) in stimulating insulin secretion in isolated rat pancreatic islet and was significantly more potent than the PEG(2k)-N(ter)-GLP-1 (P < 0.05) that showed a marked reduced potency. Furthermore, PEG(2k)-Lys-GLP-1 was clearly resistant to purified DPP-IV in buffer with 50-fold increased half-life compared to unmodified GLP-1. When PEG(2k)-Lys-GLP-1 was administered intravenously and subcutaneously into rats, PEGylation improved the half-life, which resulted in substantial improvement of the mean plasma residence time as a 16-fold increase for iv and a 3.2-fold increase for sc. These preliminary results suggest a site specifically mono-PEGylated GLP-1 greatly improved the pharmacological profiles; thus, we anticipated that it could serve as potential candidate as an antidiabetic agent for the treatment of non-insulin-dependent diabetes patients.     

Mammalian PIG-X and yeast Pbn1p are the essential components of glycosylphosphatidylinositol-mannosyltransferase I

Within the endoplasmic reticulum (ER), mannoses and glucoses, donated from dolichol-phosphate-mannose and -glucose, are transferred to N-glycan and GPI-anchor precursors, and serine/threonine residues in many proteins. Glycosyltransferases that mediate these reactions are ER-resident multitransmembrane proteins with common characteristics, forming a superfamily of >10 enzymes. Here, we report an essential component of glycosylphosphatidylinositol-mannosyltransferase I (GPI-MT-I), which transfers the first of the four mannoses in the GPI-anchor precursors. We isolated a Chinese hamster ovary (CHO) cell mutant defective in GPI-MT-I but not its catalytic component PIG-M. The mutant gene, termed phosphatidylinositolglycan-class X (PIG-X), encoded a 252-amino acid ER-resident type I transmembrane protein with a large lumenal domain. PIG-X and PIG-M formed a complex, and PIG-M expression was <10% in the absence of PIG-X, indicating that PIG-X stabilizes PIG-M. We found that Saccharomyces cerevisiae Pbn1p/YCL052Cp, which was previously reported to be involved in autoprocessing of proproteinase B, is the functional homologue of PIG-X; Pbn1p is critical for Gpi14p/YJR013Wp function, the yeast homologue of PIG-M. This is the first report of an essential subcomponent of glycosyltransferases using dolichol-phosphate-monosaccharide.     

Up-regulation of PI3K/Akt signaling by 17beta-estradiol through activation of estrogen receptor-alpha, but not estrogen receptor-beta, and stimulates cell growth in breast cancer cells

Estrogen stimulates cell proliferation in breast cancer. The biological effects of estrogen are mediated through two intracellular receptors, estrogen receptor-alpha (ERalpha) and estrogen receptor-beta (ERbeta). However, the role of ERs in the proliferative action of estrogen is not well established. Recently, it has been known that ER activates phosphatidylinositol-3-OH kinase (PI3K) through binding with the p85 regulatory subunit of PI3K. Therefore, possible mechanisms may include ER-mediated phosphoinositide metabolism with subsequent formation of phosphatidylinositol-3,4,5-trisphosphate (PIP(3)), which is generated from phosphatidylinositol 4,5-bisphosphate via PI3K activation. The present study demonstrates that 17beta-estradiol (E2) up-regulates PI3K in an ERalpha-dependent manner, but not ERbeta, and stimulates cell growth in breast cancer cells. In order to study this phenomenon, we have treated ERalpha-positive MCF-7 cells and ERalpha-negative MDA-MB-231 cells with 10nM E2. Treatment of MCF-7 cells with E2 resulted in a marked increase in PI3K (p85) expression, which paralleled an increase in phospho-Akt (Ser-473) and PIP(3) level. These observations also correlated with an increased activity to E2-induced cell proliferation. However, these effects of E2 on breast cancer cells were not observed in the MDA-MB-231 cell line, indicating that the E2-mediated up-regulation of PI3K/Akt pathway is ERalpha-dependent. These results suggest that estrogen activates PI3K/Akt signaling through ERalpha-dependent mechanism in MCF-7 cells.     

Endogenous N-cadherin in a subpopulation of MDCK cells: distribution and catenin complex composition

Epithelial (E)-cadherin plays a critical role in developing a normal epithelial phenotype but neural (N)-cadherin can disrupt epithelial shape, at least in carcinoma-derived cells. Here the normal epithelial cell line MDCK was used to select for a trypsin-sensitive (TS-MDCK) subpopulation that expresses low levels of endogenous N-cadherin. Similar amounts of E-cadherin and all catenins are found in both TS-MDCK and trypsin-resistant cells (TR-MDCK), but TS-MDCK are less phenotypically epithelioid and more motile, and junctional proteins are more detergent soluble. In TS-MDCK, N-cadherin is largely nonjunctional; a similar N-cadherin distribution and mesenchymal phenotype are found in TR-MDCK transfected to express low levels of exogenous N-cadherin. Little N-cadherin was attracted to junctions between TS-MDCK and hTERT-RPE1 cells, a retinal pigment epithelium-derived line that expresses dominantly N-cadherin. No differences were seen in E-cadherin-catenin complexes in TS- and TR-MDCK, but N-cadherin-catenin complexes in TS-MDCK have more abundant p120 catenin. Overall, the results indicate that E- and N-cadherin assemble stoichiometrically different complexes with p120 in the same cells. Further, N-cadherin does not participate with E-cadherin in a zonular epithelial junction in normal MDCK epithelial cells. Rather, even low levels of endogenous N-cadherin contribute to a disrupted epithelial phenotype, resembling the effect of N-cadherin on carcinoma-derived epithelial cells.     

Bcl-2 expression suppresses mismatch repair activity through inhibition of E2F transcriptional activity

Bcl-2 stimulates mutagenesis after the exposure of cells to DNA-damaging agents. However, the biological mechanisms of Bcl-2-mediated mutagenesis have remained largely obscure. Here we demonstrate that the Bcl-2-mediated suppression of hMSH2 expression results in a reduced cellular capacity to repair mismatches. The pathway linking Bcl-2 expression to the suppression of mismatch repair (MMR) activity involves the hypophosphorylation of pRb, and then the enhancement of the E2F-pRb complex. This is followed by a decrease in hMSH2 expression. MMR has a key role in protection against deleterious mutation accumulation and in maintaining genomic stability. Therefore, the decreased MMR activity by Bcl-2 may be an underlying mechanism for Bcl-2-promoted oncogenesis.     

A set of epitope-tagging integration vectors for functional analysis in Saccharomyces cerevisiae

Functional analysis of genes from Saccharomyces cerevisiae has been the major goal after determination of genome sequences. Even though several tools for molecular-genetic analyses have been developed, only a limited number of reliable genetic tools are available to support functional assay at protein level. Epitope tagging is a powerful tool for detecting, purifying, and functional studying of proteins. But systematic tagging systems developed with integration vectors are not available. Here, we have constructed a set of integration vectors allowing a translational fusion of interested proteins to the four different epitope tags (HA, Myc, Flag, and GFP). To confirm function and expression of C-terminal-tagged proteins, we used Cdc11, a component of the septin filament that encircles the mother bud neck and consists of five major proteins: Cdc3, Cdc10, Cdc11, Cdc12, and Sep7. The tagged version of Cdc11 expressed under its endogenous promoter was found to be physiologically functional, as evidenced by localization at the neck and suppression of the growth defect associated with the temperature-sensitive mutation of cdc11-6. The expressed proteins were efficiently detected with antibodies against Cdc11 or the epitopes. When immunoprecipitated with anti-Myc antibody, each septin protein tagged with Myc was effectively copurified with other septin components, indicating formation of a stable septin complex. Because the modules of the tags were located under the same array of eighteen restriction sites on integration vectors containing four different markers (HIS3, TRP1, LEU2, or URA3), this tagging system provides efficient multiple tagging and stable expression of a gene of interest.     

Eutectic formation analysis of amino acid mixtures using molecular dynamics simulations

The mechanism of eutectic formation was investigated via computer-aided molecular dynamics techniques based on experimental results. The CBZ group mixtures CBZ-l-Asp/d-AlaNH2 x HCl/methanol, CBZ-l-Asp/l-PheOMe x HCl/methanol, and CBZ-l-Tyr/l-ArgNH2 x 2HCl/methanol formed transparent eutectic melts. The non-CBZ group mixtures l-Asp/d-AlaNH2 x HCl/methanol, l-Asp/l-PheOMe x HCl/methanol, and l-Tyr/l-ArgNH2 x 2HCl/methanol did not form eutectic melts. According to molecular dynamics simulation results, increase in the kinetic energy values of eutectic forming mixtures was much larger than the increase in potential energy over a temperature shift from 298 to 333 K. However, the results for non-eutectic forming mixtures were reversed. The Coulomb interaction energies of eutectic forming mixtures significantly decreased, because eutectic melting can increase the mobility of molecules in the mixtures. The enhancement of molecular mobility was confirmed by increased self-diffusion constant values, and the change of solid-to-liquid phase was detected by radial distribution function results. The periodic boundary conditions for calculation of molecular dynamics were found to be reliable.     

Crystal structures of apo-form and binary/ternary complexes of Podophyllum secoisolariciresinol dehydrogenase, an enzyme involved in formation of health-protecting and plant defense lignans

(-)-Matairesinol is a central biosynthetic intermediate to numerous 8-8'-lignans, including the antiviral agent podophyllotoxin in Podophyllum species and its semi-synthetic anticancer derivatives teniposide, etoposide, and Etopophos. It is formed by action of an enantiospecific secoisolariciresinol dehydrogenase, an NAD(H)-dependent oxidoreductase that catalyzes the conversion of (-)-secoisolariciresinol. Matairesinol is also a plant-derived precursor of the cancer-preventative "mammalian" lignan or "phytoestrogen" enterolactone, formed in the gut following ingestion of high fiber dietary foodstuffs, for example. Additionally, secoisolariciresinol dehydrogenase is involved in pathways to important plant defense molecules, such as plicatic acid in the western red cedar (Thuja plicata) heartwood. To understand the molecular and enantiospecific basis of Podophyllum secoisolariciresinol dehydrogenase, crystal structures of the apo-form and binary/ternary complexes were determined at 1.6, 2.8, and 2.0 angstrom resolution, respectively. The enzyme is a homotetramer, consisting of an alpha/beta single domain monomer containing seven parallel beta-strands flanked by eight alpha-helices on both sides. Its overall monomeric structure is similar to that of NAD(H)-dependent short-chain dehydrogenases/reductases, with a conserved Asp47 forming a hydrogen bond with both hydroxyl groups of the adenine ribose of NAD(H), and thus specificity toward NAD(H) instead of NADP(H). The highly conserved catalytic triad (Ser153, Tyr167, and Lys171) is adjacent to both NAD(+) and substrate molecules, where Tyr167 functions as a general base. Following analysis of high resolution structures of the apo-form and two complex forms, the molecular basis for both the enantio-specificity and the reaction mechanism of secoisolariciresinol dehydrogenase is discussed and compared with that of pinoresinol-lariciresinol reductase.