Identification of major proteins in maize egg cells

In most flowering plants, the female gametophyte develops in an ovule deeply embedded in the ovary. Through double fertilization, the egg cell fuses with the sperm cell, resulting in a zygote, which develops into the embryo. In the present study, we analyzed egg cell lysates by polyacrylamide gel electrophoresis and subsequent mass spectrometry-based proteomics technology, and identified major protein components expressed in the egg cell. The identified proteins included three cytosolic enzymes of the glycolytic pathway, glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase and triosephosphate isomerase, two mitochondrial proteins, the ATP synthase beta-subunit and an adenine nucleotide transporter, and annexin p35. In addition, expression levels of these proteins in the egg cell were compared with those in the early embryo, the central cell and the suspension cell. Annexin p35 was highly expressed only in the egg cell, and glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase and the adenine nucleotide transporter were expressed at higher levels in egg cells than in central and cultured cells. These results indicate that annexin p35 in the egg cell and zygote is involved in the exocytosis of cell wall materials, which is induced by a fertilization-triggered increase in cytosolic Ca2+ levels, and that the egg cell is rich in an enzyme subset for the energy metabolism.     

Quantitative filtration-blotting of protein in the presence of sodium dodecyl sulfate and its use for protein assay

It is thought that sodium dodecyl sulfate (SDS), an anionic detergent, binds to hydrophobic moieties of peptide to destroy the conformational structure of protein. Because of this property, it is involved in many biochemical procedures such as separations of protein and proteolytic digestion. In the course of our study on a solid-phase protein assay, we found that SDS acts as an effective reagent for protein blotting onto a hydrophobic membrane of polyvinylidene difluoride with a manifold dot-blot apparatus. At least 0.1% SDS in an acid-ethanol blotting solution, while reducing the bias of pronounced interferers for protein assay to protein-membrane interaction, quantitatively retains protein on the membrane. Presumably, protein denatures by SDS to become an unfolded state and adsorbs into the membrane by hydrophobic interaction, even in the presence of excess SDS. Therefore, bolts stained with a pyrogallol red-molybdate complex (Pyromolex) reagent unreactive to the membrane allowed a precise protein determination without significant interference of materials, especially detergents in the sample solution. The filtration-blotting with SDS would be a crucial procedure for quantitative analyses such as immunoblotting in detergent-containing samples, together with the solid-phase protein assay with limited sample volumes, such as 20 microL or less.     

Proteasome inhibition induces inclusion bodies associated with intermediate filaments and fragmentation of the Golgi apparatus

The ubiquitin-proteasome system is involved in a variety of biological processes. Inclusion bodies associated with intermediate filaments (IFs) and ubiquitin are observed in various diseases; however, the precise mechanisms of formation and the pathological significance of inclusion bodies have not been fully understood. We examined the effect of proteasome inhibitors on the structure of IF using anti-cytokeratin antibodies or transfection of green fluorescent protein-fused cytokeratin 18 in a hepatoma cell line, Huh7. Intracellular organelles were visualized by immunofluorescent and electron microscopies. Proteasome inhibitors induced IF inclusions associated with ubiquitin. Electron microscopic examination revealed inclusion bodies surrounded by filamentous structures. Autophagic vacuoles and lysosomes were frequently observed, and the organization of the Golgi apparatus was disrupted in these cells. After the removal of the proteasome inhibitors, the IF network and organization of the Golgi apparatus were restored. The IF inclusions could be induced by inhibition of the proteasome function. IF inclusions induced fragmentation of the Golgi apparatus and might inhibit the function of this important station of membrane traffic. The IF inclusions disappeared by restoring proteasome function, and autophagy and lysosomal degradation might be, at least in part, associated with the elimination of inclusion bodies.     

Solution structure of the DFF-C domain of DFF45/ICAD. A structural basis for the regulation of apoptotic DNA fragmentation

DFF45/ICAD has dual functions in the final stage of apoptosis, by acting as both a folding chaperone and a DNase inhibitor of DFF40/CAD. Here, we present the solution structure of the C-terminal domain of DFF45, which is essential for its chaperone-like activity. The structure of this domain (DFF-C) consists of four alpha helices, which are folded in a novel helix-packing arrangement. The 3D structure reveals a large cluster of negatively charged residues on the molecular surface of DFF-C. This observation suggests that charge complementation plays an important role in the interaction of DFF-C with the positively charged catalytic domain of DFF40, and thus for the chaperone activity of DFF45. The structure of DFF-C also provides a rationale for the loss of the chaperone activity in DFF35, a short isoform of DFF45. Indeed, in DFF35, the amino acid sequence is truncated in the middle of the second alpha helix constituting the structure of DFF-C, and thus both the hydrophobic core and the cluster of negative charges are disrupted.     

Structure and thermodynamics of the extraordinarily stable molten globule state of canine milk lysozyme

Here, we show that an unfolded intermediate of canine milk lysozyme is extraordinarily stable compared with that of the other members of the lysozyme-alpha-lactalbumin superfamily, which has been studied previously. The stability of the intermediate of this protein was investigated using calorimetry, CD spectroscopy, and NMR spectroscopy, and the results were interpreted in terms of the structure revealed by X-ray crystallography at a resolution of 1.85 A to an R-factor of 17.8%. On the basis of the results of the thermal unfolding, this protein unfolds in two clear cooperative stages, and the melting temperature from the intermediate to the unfolded states is about 20 degrees C higher than that of equine milk lysozyme. Furthermore, the (1)H NMR spectra of canine milk lysozyme at 60 degrees C, essentially 100% of which exists in the intermediate, showed that small resonance peaks that arise from ring-current shifts of aliphatic protons are still present in the upfield region from 0 to -1 ppm. The protein at this temperature (60 degrees C) and pH 4.5 has been found to bind 1-anilino-naphthalene-8-sulfonate (ANS) with enhancement of the fluorescence intensity compared with that of native and thermally unfolded states. We interpret that the extraordinarily stable intermediate is a molten globule state, and the extraordinary stabilization of the molten globule state comes from stronger protection around the C- and D-helix of the aromatic cluster region due to the His-21 residue. The conclusion helps to explain how the molten globule state acquires its structure and stability.