Changes in the reactivity of proteins of rat liver ribosomes against [C]iodoacetamide depending on their organization in ribosomal subparticles, 80S ribosomes and on the attachment of poly-(U)

(1) The isolated mixtures of ribosomal proteins can be substituted by [¹⁴C]-iodoacetamide up to an average of about 2 equivalents per 20 000 dalton. The extent of substitution of single proteins measured after two-dimensional polyacrylamide gel electrophoresis shows that all proteins are reactive.

(2) Also in the subunits, all proteins are accessible to substitution. Compared with isolated proteins, however, the reactivity is decreased and the amount of labelling for most proteins ranges as low as 5 to 20%.

(3) Reassociation of ribosomal subunits decreases the reactivity of 12 proteins of the small subunit and that of 20 proteins of the large subunit.

(4) The presence of messenger inhibits the substitution of 10 proteins of the small subunit and of 6 proteins of the large one.

(5) Seven proteins of the small subunit and 3 proteins of the large one are influenced both by the other subunit and by messenger-RNA.     

Synthesis of Proteins Enriched in Li+- Induced Vegetalized Embryos of Sea Urchin during Early Development

Sea urchin embryos were vegetalized by a pulse treatment with 60 mM Li⁺ between 2.5 hr and 6 hr after fertilization at 20°C. Normal and Li⁺ -treated embryos were exposed to [³⁵S]-methionine for 2 hr at various stages and [³⁵S]-labeled proteins were analyzed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). On fluorograph of 2D-PAGE at the pre-hatching blastula stage, significant difference of labeled proteins between normal and vegetalized embryos was not observed in the range from neutral to acidic pH, but pls of several proteins were found to be shifted toward alkaline pH. At the mesechyme blastula stage, five major proteins [M.W. 36 K, 43 K (two species), 71 K and 150 K] were enriched in Li⁺-treated embryos among a few hundreds of synthesized proteins. At the late gastrula stage, the labeling intensities of these proteins except for one of 43 K proteins increased remarkably in Li⁺-treated embryos. Furthermore, two proteins (M.W. 105 K and 135 K) were also enriched in Li⁺-treated embryos at this stage. At the prism stage, these proteins enriched in Li⁺-treated embryos became hardly detectable, and the synthesis of at least four proteins (M.W. about 20 K, 41 K, 43 K and 200 K<) appeared to increase in normal embryos, but not in Li⁺-treated embryos. Synthesis of proteins eniched in Li⁺-treated embryos probably support endodermal cell differentiation.     

Ultrastructural localization of highly variable 185/333 immune response proteins in the coelomocytes of the sea urchin, Heliocidaris erythrogramma

The 185/333 proteins of sea urchins represent a family of highly variable immune response molecules with unknown functions. In this study, we show that 185/333 proteins are expressed by three cell types: amoebocytes, colourless spherule cells and gut-associated amoebocytes. A sub-population of amoebocytes express 185/333 proteins on the membranes of vesicles emanating from the trans-Golgi and which later fuse with the plasma membranes of the cells. The previously uncharacterized gut-associated amoebocytes also show a high level of 185/333 protein expression on their internal vesicles and plasma membranes. Colourless spherule cells contain 185/333 proteins within large spherules (specialized intracellular vesicles). In the presence of bacteria and yeast, the ultrastucture of colourless spherule cells changes and 185/333 proteins disappear. In contrast, 185/333 proteins were not found in the phagosomes of coelomocytes. The 185/333-positive gut amoebocytes were often associated with anuclear bodies, which appeared to incorporate material of microbial origin that was surrounded by 185/333 proteins. The association between 185/333 proteins on gut amoebocytes and anuclear bodies suggests that these proteins may be involved in the phagocytosis of microbes in the gut epithelium.     

RGS17/RGSZ2 and the RZ/A family of regulators of G-protein signaling

Regulators of G-protein signaling (RGS proteins) comprise over 20 different proteins that have been classified into subfamilies on the basis of structural homology. The RZ/A family includes RGSZ2/RGS17 (the most recently discovered member of this family), GAIP/RGS19, RGSZ1/RGS20, and the RGSZ1 variant Ret-RGS. The RGS proteins are GTPase activating proteins (GAPs) that turn off G-proteins and thus negatively regulate the signaling of G-protein coupled receptors (GPCRs). In addition, some RZ/A family RGS proteins are able to modify signaling through interactions with adapter proteins (such as GIPC and GIPN). The RZ/A proteins have a simple structure that includes a conserved amino-terminal cysteine string motif, RGS box and short carboxyl-terminal, which confer GAP activity (RGS box) and the ability to undergo covalent modification and interact with other proteins (amino-terminal). This review focuses on RGS17 and its RZ/A sibling proteins and discusses the similarities and differences among these proteins in terms of their palmitoylation, phosphorylation, intracellular localization and interactions with GPCRs and adapter proteins. The specificity of these RGS protein for different Galpha proteins and receptors, and the consequences for signaling are discussed. The tissue and brain distribution, and the evolving understanding of the roles of this family of RGS proteins in receptor signaling and brain function are highlighted.     

Analysis of the Formation of the Animal-Vegetal Axis during Xenopus Oogenesis Using Monoclonal Antibodies

Maternally accumulated materials in Xenopus oocytes, in particular mRNAs and proteins, are considered to participate in the determination of the developmental specification of embryonic cells. In this study, a large number of monoclonal antibodies was raised against bulk oocyte antigens to examine patterns of intracellular distribution of oocyte proteins. Immunohistochemical experiments with mature oocytes showed that there are five different patterns of distribution of oocyte proteins, with enrichment on the animal side (type A₁, and A₂ ptoteins), vegetal side (type V₁ and V₂ proteins), and in the peripheral cytoplasm (type P proteins). Clear localization of type A and V antigen proteins occurred at Dumont's stages IV-VI. However, at the preceding stages, the distributions of these antigen proteins appeared to be homogeneous. By contrast, the pattern of distribution of type P protenis did not change markedly throughout oogenesis. The presence of type A and type V antigen proteins reflected the animal-vegetal axis in the cytoplasm of the mature oocyte. Furthermore, there were two boundaries of the distributions of proteins at the equatorial region, excluding or including the cytoplasm around the germinal vesicle. Thus, the cytoplasm of mature oocytes was multilayered with respect to the different proteins distributed along the animal-vegetal axis.     

A large complement of the predicted Arabidopsis ARM repeat proteins are members of the U-box E3 ubiquitin ligase family

The Arabidopsis genome was searched to identify predicted proteins containing armadillo (ARM) repeats, a motif known to mediate protein-protein interactions in a number of different animal proteins. Using domain database predictions and models generated in this study, 108 Arabidopsis proteins were identified that contained a minimum of two ARM repeats with the majority of proteins containing four to eight ARM repeats. Clustering analysis showed that the 108 predicted Arabidopsis ARM repeat proteins could be divided into multiple groups with wide differences in their domain compositions and organizations. Interestingly, 41 of the 108 Arabidopsis ARM repeat proteins contained a U-box, a motif present in a family of E3 ligases, and these proteins represented the largest class of Arabidopsis ARM repeat proteins. In 14 of these U-box/ARM repeat proteins, there was also a novel conserved domain identified in the N-terminal region. Based on the phylogenetic tree, representative U-box/ARM repeat proteins were selected for further study. RNA-blot analyses revealed that these U-box/ARM proteins are expressed in a variety of tissues in Arabidopsis. In addition, the selected U-box/ARM proteins were found to be functional E3 ubiquitin ligases. Thus, these U-box/ARM proteins represent a new family of E3 ligases in Arabidopsis.     

Comparative study between prokaryotes and eukaryotes by chemical iodination of ribosomal proteins.

Escherichia coli and Saccharomyces cerevisiae ribosomal proteins were chemically iodinated with 125I by chloramine T under conditions in which the proteins were denatured. The labelled proteins were subsequently separated by two-dimensional gel electrophoresis with an excess of untreated ribosomal proteins from the same species. The iodination did not change the electrophoretic mobility of the proteins as shown by the pattern of spots in the stained gel slabs and their autoradiography. The 125I radioactivity incorporated in the proteins was estimated by cutting out the gel spots from the two-dimensional electrophoresis gel slabs. The highest content of 125I was found in the ribosomal proteins L2, L11, L13, L20/S12, S4 and S9 from E. coli, and L2/L3, L4/L6/S7, L5, L19/L20, L22/S17, L29/S27, L35/L37 and S14/S15 from S. cerevisiae. Comparisons between the electrophoretic patterns of E. coli and S. cerevisiae ribosomal proteins were carried out by coelectrophoresis of labelled and unlabelled proteins from both species. E. coli ribosomal proteins L5, L11, L20, S2, S3 and S15/S16 were found to overlap with L15, L11/L16, L36/L37, S3, S10 and S33 from S. cerevisiae, respectively. Similar coelectrophoresis of E. coli 125I-labelled proteins with unlabelled rat liver and wheat germ ribosomal proteins showed the former to overlap with proteins L1, L11, L14, L16, L19, L20 and the latter with L2, L5, L6, L15, L17 from E. coli.     

The essential role of mitochondria in the biogenesis of cellular iron-sulfur proteins

Iron-sulfur (Fe/S) proteins play an important role in electron transfer processes and in various enzymatic reactions. In eukaryotic cells, known Fe/S proteins are localised in mitochondria, the cytosol and the nucleus. The biogenesis of these proteins has only recently become the focus of investigations. Mitochondria are the major site of Fe/S cluster biosynthesis in the cell. The organelles contain an Fe/S cluster biosynthesis apparatus that resembles that of prokaryotic cells. This apparatus consists of some ten proteins including a cysteine desulfurase producing elemental sulfur for biogenesis, a ferredoxin involved in reduction, and two chaperones. The mitochondrial Fe/S cluster synthesis apparatus not only assembles mitochondrial Fe/S proteins, but also initiates formation of extra-mitochondrial Fe/S proteins. This involves the export of sulfur and possibly iron from mitochondria to the cytosol, a reaction performed by the ABC transporter Atm1p of the mitochondrial inner membrane. A possible substrate of Atm1p is an Fe/S cluster that may be stabilised for transport. Constituents of the cytosol involved in the incorporation of the Fe/S cluster into apoproteins have not been described yet. Many of the mitochondrial proteins involved in Fe/S cluster formation are essential, illustrating the central importance of Fe/S proteins for life. Defects in Fe/S protein biogenesis are associated with the abnormal accumulation of iron within mitochondria and are the cause of an iron storage disease.     

Negative regulation of fibroblast motility by Ena/VASP proteins

Ena/VASP proteins have been implicated in cell motility through regulation of the actin cytoskeleton and are found at focal adhesions and the leading edge. Using overexpression, loss-of-function, and inhibitory approaches, we find that Ena/VASP proteins negatively regulate fibroblast motility. A dose-dependent decrease in movement is observed when Ena/VASP proteins are overexpressed in fibroblasts. Neutralization or deletion of all Ena/VASP proteins results in increased cell movement. Selective depletion of Ena/VASP proteins from focal adhesions, but not the leading edge, has no effect on motility. Constitutive membrane targeting of Ena/VASP proteins inhibits motility. These results are in marked contrast to current models for Ena/VASP function derived mainly from their role in the actin-driven movement of Listeria monocytogenes.     

Secretion and Uptake of 14C Proteins by Fat Body of Calpodes ethlius Stoll. (Lepidoptera, Hesperiidae)

Insect fat body from larvae of Calpodes ethlius synthesised proteins in vitro , some of which were secreted into the medium. ¹⁴C leucine was incorporated into fat-body proteins and the released proteins were characterised by electrophoresis and immunodiffusion. The released proteins included the three main proteins normally found in larval hemolymph and fat body. Larval fat body in the main synthetic phase of development did not sequester these ¹⁴C-labelled proteins when incubated with them in vitro or when they were injected into mid-instar larvae. In contrast, these proteins were sequestered by fat-body cells undergoing pupation.
The conclusion is that larval fat-body cells in the main synthetic phase selectively exclude proteins synthesised in vitro by fat body of the same age. During pupal development the fat body absorbs proteins it secreted at an earlier age.     

Proteomics analysis of the excretory/secretory component of the blood-feeding stage of the hookworm, Ancylostoma caninum

Hookworms are blood-feeding intestinal parasites of mammalian hosts and are one of the major human ailments affecting approximately 600 million people worldwide. These parasites form an intimate association with the host and are able to avoid vigorous immune responses in many ways including skewing of the response phenotype to promote parasite survival and longevity. The primary interface between the parasite and the host is the excretory/secretory component, a complex mixture of proteins, carbohydrates, and lipids secreted from the surface or oral openings of the parasite. The composition of this complex mixture is for the most part unknown but is likely to contain proteins important for the parasitic lifestyle and hence suitable as drug or vaccine targets. Using a strategy combining the traditional technology of one-dimensional SDS-PAGE and the newer fractionation technology of OFFGEL electrophoresis we identified 105 proteins from the excretory/secretory products of the blood-feeding stage of the dog hookworm, Ancylostoma caninum. Highly represented among the identified proteins were lectins, including three C-type lectins and three beta-galactoside-specific S-type galectins, as well as a number of proteases belonging to the three major classes found in nematodes, aspartic, cysteine, and metalloproteases. Interestingly 28% of the identified proteins were homologous to activation-associated secreted proteins, a family of cysteine-rich secreted proteins belonging to the sterol carrier protein/Tpx-1/Ag5/PR-1/Sc-7 (TAPS) superfamily. Thirty-four of these proteins were identified suggesting an important role in host-parasite interactions. Other protein families identified included hyaluronidases, lysozyme-like proteins, and transthyretin-like proteins. This work identified a suite of proteins important for the parasitic lifestyle and provides new insight into the biology of hookworm infection.     

Identification of flooding stress responsible cascades in root and hypocotyl of soybean using proteome analysis

Flooding inducible proteins were analyzed using a proteomic technique to understand the mechanism of soybean response to immersion in water. Soybeans were germinated for 2 days, and then subjected to flooding for 2 days. Proteins were extracted from root and hypocotyl, separated by two-dimensional polyacrylamide gel electrophoresis, stained by Coomassie brilliant blue, and analyzed by protein sequencing and mass spectrometry. Out of 803 proteins, 21 proteins were significantly up-regulated, and seven proteins were down-regulated by flooding stress. Of the total, 11 up-regulated proteins were classified as related to protein destination/storage and three proteins to energy, while four down-regulated proteins were related to protein destination/storage and three proteins to disease/defense. The expression of 22 proteins significantly changed within 1 day after flooding stress. The effects of flooding, nitrogen substitution without flooding, or flooding with aeration were analyzed for 1–4 days. The expression of alcohol dehydrogenase increased remarkably by nitrogen substitution compared to flooding. The expression of many proteins that changed due to flooding showed the same tendencies observed for nitrogen substitution; however, the expression of proteins classified into protein destination/storage did not.     

Characterization of eukaryotic cell surfaces prior to and after serum protein adsorption by X-ray photoelectron spectroscopy

Elemental surface concentration ratios N/C, O/C, and P/C of fibroblasts, HELA epithelial cells, and smooth muscle cells, prior to and after washing in the absence or presence of serum proteins, were determined by X-ray photoelectron spectroscopy. Cell surfaces appeared to adsorb hardly any serum proteins, and the relatively high P/C, as compared to N/C and O/C, elemental surface concentration ratio indicated that the cell surfaces consisted mainly of the phospholipid bilayer, with little or no proteins present. The lack of adsorption of serum proteins to the cell surfaces seems at odds with the common notion that cells require adhesive proteins in order to adhere and spread. However, the adsorption behavior of cellularly produced proteins may be completely different, particularly since they seem to be able to displace adsorbed serum proteins from biomaterials surfaces. Interestingly, only HELA epithelial cells (a tumor cell line) appeared to adsorb a very small amount of proteins.     

Dataset of the plasma membrane proteome of nasopharyngeal carcinoma cell line HNE1 for uncovering protein function

Nasopharyngeal carcinoma （NPC） is a commonly occurring tumor in southern China and Southeast Asia. The current study focused on developing an extensive analysis method for the peripheral and integral proteins of NPC cell line HNE1. The peripheral membrane proteins were extracted by biotinylated enrichment, 0.1 M Na2CO3, and H20. Integral or total plasma membrane fractions were prepared using 30% Percoll density grade centrifugation with or without 0.1 M Na2CO3 treatment and evaluated by Western blot analysis. The proteins were subjected to two-dimensional electrophoresis combined with tandem mass spectrometry, sodium dodecyl sulfate-polyacrylamide gel electrophoresis combined with tandem mass spectrometry, and shotgun analysis. We identified 371, 180, and 702 proteins from peripheral, integral, and total plasma membrane fractions, respectively. In all, 848 non-redundant proteins （534 groups） were identified. Binding, catalytic, and structural molecules were the major classes. In addition to the known cell surface markers of NPC cells, the analysis revealed 311 proteins involved in multiple cell-signaling pathways and 25 proteins in disease pathways that are characteristic of cancer cells. By searching the Differentially Expressed Protein Database（http：//protchem.hunnu.edu.cn/depd/index.jsp） ,199 proteins were found to be differentially expressed in previous cancer proteome research. A 671 protein-protein interaction network was obtained, including 178 identified proteins in this work. The plasma membrane localization of five proteins was confirmed by immunological techniques, validating this proteomic strategy. Our study could offer some help for understanding the molecular mechanism of NPC.     

Binding of [3H]Nitrendipine to Proteins in the Plasma Membrane of Sea Urchin Sperm

The plasma membrane fractions of the sperm of four species of sea urchin, obtained by the method by Podell et al. (24), gave similar electrophoretic profiles of proteins. Several proteins in the membrane fraction from Hemicentrotus pulcherrimus bound [³H]nitrendipine, a specific antagonist of voltage-dependent Ca²⁺channels, added at concentration of about 10⁴times those reported to be effective in muscle and nerve cells. Nifedipine, a close analogue of nitrendipine, decreased the bindings of [³H]nitrendipine to 210, 140, 130 and 110 kDa and increased its bindings to several other proteins. Diltiazem, another type of Ca²⁺channel blocker, enhanced the bindings of [³H]nitrendipine to proteins of 210, 140, 130 and 110 kDa, and decreased its bindings to the other proteins. This effect of diltiazem on the binding of [³H]nitrendipine to proteins in the membrane fraction was similar to its effect on the mammalian excitable membrane fraction. The proteins whose binding to [³H]nitrendipine was blocked by nifedipine and enhanced by diltiazem are Ca²⁺channels.