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At least 1,063 records · Page 59Linked to original sources
PubMed1991

Structural requirements of the cytoplasmic domains of the human macrophage Fc gamma receptor IIa and B cell Fc gamma receptor IIb2 for the endocytosis of immune complexes.

Two isotypes of the monocyte/macrophage as well as B cell Fc gamma receptor type II (FcRIIa and FcRIIb2, respectively) mainly differ in the length (76 vs. 44 amino acids) and amino acid sequence of their cytoplasmic domains. Only the eight amino acids just behind the putative transmembrane region are identical. Despite this marked difference, both FcRII mediate endocytosis of immune complexes. To determine the functional significance of the cytoplasmic domains, we expressed truncated FcRIIa and FcRIIb2 in FcR- BHK-21 cells. Mutants of both receptors containing only one amino acid (tail-minus) of the cytoplasmic domain failed to mediate immune complex uptake. The significance of the cytoplasmic domain of the receptors could be further demonstrated using a chimeric FcRIII-FcRIIa construct. Therefore we expressed an FcRIII lacking the hydrophobic carboxyl terminus (containing the putative phosphatidyl - inositol - glycan anchor site) fused inframe to the transmembrane and cytoplasmic domain of the FcRIIa in BHK-21 cells. In contrast to the wild type FcRIII, this chimeric receptor mediated immune complex uptake indistinguishable from that mediated by the FcRIIa. Receptor mutants with relatively short cytoplasmic domains (FcRIIb2: 13, and FcRIIa: 16 amino acids) revealed, that these short amino acid stretches are sufficient to allow reduced receptor-mediated endocytosis of bound ligand. Furthermore, using FcRIIa deletion mutants with a cytoplasmic domain consisting of 62, 46, and 28 amino acids, respectively, we found that the capability of these mutants to mediate immune complex uptake decreased gradually with the truncation of the cytoplasmic tails. Thus, only short amino acid sequences of the cytoplasmic domain are sufficient to enable an, albeit reduced, receptor-mediated endocytosis.

Animals↗
PubMed1987

Subcellular localization of enzymes in Streptomyces aureofaciens and its alteration by benzyl thiocyanate. I. Phosphatases and ATP-glucokinase.

Mycelia of a low- and a high-production strain of Streptomyces aureofaciens were converted into protoplasts and divided into five subcellular fractions in order to localize exopolyphosphatases (EC 3.6.1.11), triphosphatase (EC 3.6.1.25), inorganic diphosphatase (EC 3.6.1.1), apyrase (EC 3.6.1.5) and glucokinase (EC 2.7.1.2). The highest specific activity of enzymes hydrolyzing polyphosphates was found in cytoplasmic vesicles and membranes. Triphosphatase was detected in the periplasmic fraction. Periplasmic vesicles and cytoplasm exhibited a high activity of diphosphatase. Apyrase was found mainly in the fractions of membranes and cytoplasmic vesicles. Glucokinase was a cytoplasmic enzyme. The enzymes were released from membrane structures into cytoplasm or periplasmic space if benzyl thiocyanate (10 microM) was present in the growth medium.

Cations↗
PubMed1977

Structural heterogeneity of the cytoplasmic and outer membranes of Escherichia coli.

The cytoplasmic and outer membranes of gram-negative bacteria can be isolated from spheroplasts, and separated on sucrose density gradients. Lysis of spheroplasts causes extensive membrane fragmentation and since the characteristics of the fragments obtained by different lysis procedures need not be identical, the influence of the disruption method on membrane composition has been examined. Spheroplasts of Escherichia coli J5 were lysed by osmotic shock, which did not significantly separate the cytoplasmic and outer membranes, but resulted in mixed membrane vesicles. Lysis in the French press and by sonication caused extensive membrane fragmentation and separation. Sonication, however, also caused some fusion between fragments of the outer and the cytoplasmic membranes; this intermembrane fusion increased with sonication time. When the cytoplasmic and outer membranes were well separated and intermembrane fusion was minimal or absent, the cytoplasmic and outer membrane fragments were heterogeneous with respect to density and ovarll phospholipid, protein and lipopolysaccharide composition. In addition, cytoplasmic, but not outer, membrane fragments were also heterogeneous with respect to protein composition. It is concluded, therefore, that membrane fragments obtained from the cytoplasmic and outer membranes are heterogeneous independently of the lysis procedures used to obtain these fragments. Possible reasons for this heterogeneity are discussed.

Bacterial Proteins↗
PubMed2005

Electrochemical structure of the crowded cytoplasm.

The current view of the cytoplasm as a 'bustling and well-organized metropolitan city' raises the issue of how physicochemical forces control the macromolecular interactions and transport of metabolites and energy in the cell. Motivated by studies on bacterial osmosensors, we argue that charged cytoplasmic macromolecules are stabilized electrostatically by their ionic atmospheres. The high cytoplasmic crowding (25-50% of cell volume) shapes the remaining cell volume (50-75%) into transient networks of electrolyte pathways and pools. The predicted 'semi-conductivity' of the electrolyte pathways guides the flow of biochemical ions throughout the cytoplasm. This metabolic and signaling current is powered by variable electrochemical gradients between the pools. The electrochemical gradients are brought about by cellular biochemical reactions and by extracellular stimuli. The cellular metabolism is thus vectorial not only across the membrane but also throughout the cytoplasm.

Animals↗
PubMed2001

High throughput screening: a rapid way to recombinant allergens.

Complex allergenic sources such as moulds, foods and mites contain large panels of IgE-binding molecules which need to be cloned, produced and characterized in order to mimic the entire allergenicity of whole extracts reconstituted by mixing single standardized recombinant allergens. Phage display of cDNA libraries allows selective enrichment of allergen-expressing clones using IgE from allergic patients. For the characterization of all different clones present in enriched cDNA libraries in a fast and cost-effective way, however, high-throughput screening technology is required. We have used a high-throughput, quantitative technology for fast identification of all different clones present in selectively enriched phage surface-displayed cDNA libraries in order to characterize whole allergenic repertoires from complex allergenic sources. The strategy, based on a combination of phage display and high-density arrays, allowed fast discovery of panels of related structures from different allergenic sources. They cover secreted, cytoplasmic and structural proteins with or without enzymatic activity and offer a rational explanation for the IgE-mediated cross-reactivity frequently encountered in clinical practice.

Allergens↗
PubMed1977

Lipid and protein segregation in Escherichia coli membrane: morphological and structural study of different cytoplasmic membrane fractions.

Lipid and protein segregations can be induced in E. coli cytoplasmic membranes by conformational transitions of their lipid hydrocarbon chains from a disordered to an ordered state. For E. coli strain K 1059 (an unsaturated fatty acid auxotroph) supplemented with linolenic acid, the segregation leads to large areas of membrane surfaces having distinctly different morphological characteristics (smooth compared with strongly particulated fracture faces, as visualized by freeze fracture electron microscopy). The different regions are physically separated by osmotic lysis of spheroplasts at temperatures below those of the order-disorder transition of the lipid hydrocarbon chains. The analysis of the different cytoplasmic membrane fractions provides a direct demonstration and allows a direct analysis of the segregation. As compared to the nonfractionated membranes, the membrane regions corresponding to the smooth fracture surfaces are poor in proteins, rich in lipids, and enriched in saturated fatty acids, while the membrane regions corresponding to the strongly particulated fracture surfaces are rich in proteins, poor in lipids, and enriched in unsaturated fatty acids. Quantitative information about the extent of these segregations is obtained from high-angle x-ray diffraction of the different membrane fractions and of the corresponding total lipid extracts.

Cell Membrane↗
PubMed1985

Molecular structure of the human cytoplasmic beta-actin gene: interspecies homology of sequences in the introns.

A recombinant phage that carries the cytoplasmic beta-actin gene was isolated from a human DNA library. The nucleotide sequence of this gene was determined. The amino acid sequence deduced from the nucleotide sequence matches perfectly that of beta-actin from human fibroblasts. The gene contains five introns. A large intron was found in the 5' untranslated region six nucleotides upstream from the ATG initiation codon. Four introns were found within the coding region at codons specifying amino acids 41/42, 121/122, 267, and 327/328. In contrast to the human cardiac muscle actin gene, the aorta-type smooth muscle actin gene, and the stomach-type smooth muscle actin gene, the beta-actin gene lacks the codon for cysteine between the ATG initiation codon and the codon for the NH2-terminal amino acid of the mature protein. Hybridization of genomic DNA with DNA fragments derived from intron I in the 5' untranslated region and from intron III strongly suggests the presence of a single beta-actin gene in the human genome. The DNA sequences of the coding region, of the 3' untranslated region, and of the sequence block between the "CCAAT" box and "TATA" box in the 5' flanking DNA of the human beta-actin gene are highly homologous to the corresponding sequences of the rat and chicken beta-actin genes. Unexpectedly, the sequence of intron III of the human beta-actin gene shows considerable homology to that of the rat beta-actin gene.

Actins↗