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At least 1,369 records · Page 76Linked to original sources
PubMed1988

Identification, transmembrane orientation and biogenesis of the amyloid A4 precursor of Alzheimer's disease.

The precursor of the Alzheimer's disease-specific amyloid A4 protein is an integral, glycosylated membrane protein which spans the bilayer once. The carboxy-terminal domain of 47 residues was located at the cytoplasmic site of the membrane. The three domains following the transient signal sequence of 17 residues face the opposite side of the membrane. The C-terminal 100 residues of the precursor comprising the amyloid A4 part and the cytoplasmic domain have a high tendency to aggregate, and proteinase K treatment results in peptides of the size of amyloid A4. This finding suggests that there is a precursor-product relationship between precursor and amyloid A4 and we conclude that besides proteolytic cleavage other events such as post-translational modification and membrane injury are primary events that precede the release of the small aggregating amyloid A4 subunit.

Alzheimer Disease↗
PubMed1988

Biogenesis of the yeast lysosome (vacuole): biosynthesis and maturation of proteinase yscB.

The biosynthesis and processing of the vacuolar (lysosomal) proteinase yscB was followed in vivo and in vitro. In vitro transcription--translation of the cloned proteinase yscB gene results in a high mol. wt precursor protein (HMr-precursor) of Mr = 73,000. In vivo a precursor of identical mol. wt is found in sec6l mutant cells deficient in translocation of secretory protein precursors into the lumen of the endoplasmic reticulum (ER). In contrast to N-glycosylated intermediate mol. wt forms of proteinase yscB, the HMr-precursor of the enzyme is not N-glycosylated, indicating its appearance outside the ER. sec18 Mutant cells, wild type for translocation of proteins into the ER but blocked in the delivery step of secretory proteins to the Golgi apparatus, accumulate a lower mol. wt precursor (LMr-precursor) of proteinase yscB of Mr = 41,500. Processing of the HMr-precursor of proteinase yscB to the LMr-precursor requires proteolytic cleavage which is independent of the proteinase yscA gene product, a protein known to be involved in the processing event of the LMr-precursor of proteinase yscB to the mature enzyme of Mr = 33,000. A LMr-precursor of proteinase yscB of Mr = 42,000 accumulates in proteinase yscA-deficient mutant cells (allele pep4-3). This form is enzymatically active. Incubation in vitro of the LMr-precursor of proteinase yscB with mature proteinase yscA leads to further activation and to processing of the enzyme yielding the mature 33,000 Mr protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Fungal Proteins↗
PubMed1989

Characterization of the END1 gene required for vacuole biogenesis and gluconeogenic growth of budding yeast.

The Saccharomyces cerevisiae END1 gene is required for formation or maintenance of the vacuole, for growth on non-fermentable carbon sources, for efficient mating and for growth at 37 degrees C. The END1 gene was cloned by complementation of the end1 mutation. Two end1 null mutants, constructed by disruption and deletion of the END1 gene, show features identical to the original end1 mutant. However, in this paper we correct a previous finding from our group that end1 is defective in internalization of the yeast pheromone alpha-factor. End1 mutants take up alpha-factor at the same rate as corresponding wild-type cells but the internalized pheromone is not degraded. Since whole cell respiration and respiratory control of end1 mitochondria are not impaired, it seems plausible that a defect in gluconeogenesis could partially account for the inability of end1 to grow on non-fermentable carbon sources. DNA sequence analysis of the END1 gene reveals a 3090-bp open reading frame capable of encoding a hydrophilic protein of 118 kd. The molecular mass of End1p was confirmed by immunoprecipitation. The predicted End1p sequence shows no significant similarity to other known protein sequences except for a short region of homology with the putative adenine nucleotide binding sites shared by a group of enzymes, notably ATPases.

Adenine Nucleotides↗
PubMed1992

A novel extensin that may organize extracellular matrix biogenesis in Volvox carteri.

ISG is a sulphated, extracellular glycoprotein synthesized for only a few minutes in inverting Volvox embryos and inverting sperm cell packets. This control operates at the level of transcription. ISG has been characterized by studies of protein chemistry and electron microscopy. The primary structure of ISG has been derived from genomic DNA and cDNA. ISG is composed of a globular and a rod-shaped domain. The rod-shaped domain represents a member of the extensin family with numerous repeats of Ser-(Hyp)4-6 motifs. A synthetic decapeptide matching the C-terminal sequence is able to disaggregate the organism into individual cells. Immunofluorescence microscopy localizes ISG within the boundary zone of the ECM.

Amino Acid Sequence↗
PubMed1993

Biogenesis of von Willebrand factor-containing organelles in heterologous transfected CV-1 cells.

Von Willebrand factor (vWF) is a multimeric protein involved in the adhesion of platelets to an injured vessel wall. vWF is synthesized by the endothelial cell and the megakaryocyte as a precursor protein (pro-vWF) that consists of four repeated domains, denoted D1-D2-D'-D3-A1-A2-A3-D4-B1-B2-B3-C1-C2. Previously, we have defined the domains on the pro-vWF molecule involved in dimerization as well as the domains involved in multimer assembly of vWF dimers. In the endothelial cell, part of the vWF multimers is stored in specialized organelles, the Weibel-Palade bodies. By using immunoelectron microscopy, we demonstrate that upon expression of full-length vWF cDNA, vWF-containing organelles are encountered in monkey kidney CV-1 cells that are morphologically similar to the endothelial-specific Weibel-Palade bodies. Expression in CV-1 cells of a series of vWF cDNA deletion mutants, lacking one or more domains, revealed that only those vWF mutant proteins that are able to assemble into multimers are encountered in dense-cored vesicles. Our data show that this process is independent of a particular domain on vWF and indicate that a 'condensed', multimeric vWF is required for targeting to the Weibel-Palade body.

Amino Acid Sequence↗
PubMed1993

Bradyrhizobium japonicum TlpA, a novel membrane-anchored thioredoxin-like protein involved in the biogenesis of cytochrome aa3 and development of symbiosis.

We report the discovery of a bacterial gene, tlpA, that codes for a hitherto unknown type of thioredoxin-like protein. The gene was found in the course of studying a Tn5 insertion mutant of the soybean root nodule symbiont Bradyrhizobium japonicum. The TlpA protein shared up to 31% amino acid sequence identity with various eukaryotic and prokaryotic thioredoxins and protein disulfide isomerases, and possessed a characteristic active-site sequence, Trp-Cys-Val-Pro-Cys. In contrast to all members of the thioredoxin family known to date, TlpA was shown to be anchored to the cytoplasmic membrane by means of an N-terminal transmembrane domain, while the active site-containing part of the protein faced the periplasm. The tlpA mutant had a pleiotropic phenotype in that it was defective in the development of a nitrogen fixing endosymbiosis and exhibited a strongly decreased oxidase activity, as compared with the wild-type. Holocytochrome aa3 was spectroscopically undetectable in the mutant, whereas the apoprotein of subunit one (CoxA) of this oxidase was still synthesized and incorporated into the cytoplasmic membrane. Since cytochrome aa3 is not a prerequisite for the development of symbiosis, the results suggest that TlpA is involved in at least two independent cellular processes, one of which is an essential periplasmic step in the maturation of cytochrome aa3.

Alkaline Phosphatase↗
PubMed1984

Mitochondrial membrane biogenesis: characterization and use of pet mutants to clone the nuclear gene coding for subunit V of yeast cytochrome c oxidase.

A nuclear pet mutant of Saccharomyces cerevisiae that is defective in the structural gene for subunit V of cytochrome c oxidase has been identified and used to clone the subunit V gene (COX5) by complementation. This mutant, E4-238 [24], and its revertant, JM110, produce variant forms of subunit V. In comparison to the wild-type polypeptide (Mr = 12,500), the polypeptides from E4-238 and JM110 have apparent molecular weights of 9,500 and 13,500, respectively. These mutations directly alter the subunit V structural gene rather than a gene required for posttranslational processing or modification of subunit V because they are cis-acting in diploid cells; that is, both parental forms of subunit V are produced in heteroallelic diploids formed from crosses between the mutant, revertant, and wild type. Several plasmids containing the COX5 gene were isolated by transformation of JM28, a derivative of E4-238, with DNA from a yeast nuclear DNA library in the vector YEp13. One plasmid, YEp13-511, with a DNA insert of 4.8 kilobases, was characterized in detail. It restores respiratory competency and cytochrome oxidase activity in JM28, encodes a new form of subunit V that is functionally assembled into mitochondria, and is capable of selecting mRNA for subunit V. The availability of mutants altered in the structural gene for subunit V (COX5) and of the COX5 gene on a plasmid, together with the demonstration that plasmid-encoded subunit V is able to assemble into a functional holocytochrome c oxidase, enables molecular genetic studies of subunit V assembly into mitochondria and holocytochrome c oxidase.

Cloning, Molecular↗
PubMed1980

Studies on the biogenesis of an enzymatically active complex III of the respiratory chain from yeast mitochondria.

Complex III isolated from yeast mitochondria catalyzed an antimycin A and Diuron-sensitive coenzyme QH2-cytochrome c reductase activity with a turnover number of 15.7 sec(-1) and contained 10 nmoles of cytochrome b and 4.6 nmoles of cytochrome c1 per mg of protein. Electrophoresis in sodium dodecyl sulfate acrylamide gels resolved Complex III into 10 bands with apparent molecular weights of 50,000, 40,000, 30,000, 29,000, 24,000, 17,000, 16,000, 12,000, 8,400, and 5,800. Yeast cells were labeled under nongrowing conditions with (35S)-methionine in the absence or presence of inhibitors of cytoplasmic or mitochondrial protein synthesis. Labeled Complex III was isolated by immunoprecipitation from detergent-solubilized mitochondria using anti-serum raised against the purified complex. Analysis of the immunoprecipitates by polyacrylamide gel electrophoresis revealed that a 30,000-dalton protein, cytochrome b, as well as 16,000-dalton protein were labeled in the presence of cycloheximide, indicating that they are products of mitochondrial protein synthesis. Immunoprecipitates from mitochondria obtained from cells labeled in the presence of chloramphenicol contained a new radioactive peak with a molecular weight of 100,000. In addition, significant decreases in the labeling of the proteins with molecular weights of 50,000, 40,000, 30,000, and 16,000 were observed. When Complex III was isolated by immunoprecipitation from intact spheroplasts after a 5-minute pulse with (35S)-methionine, the 100,000-dalton protein was labeled in the immunoprecipitate whether or not chloramphenicol was present; however, after a 1-hour chase with unlabeled methionine, decreased labeling of the 100,000-dalton protein was observed concomitant with an increased labeling of the 50,000- and 40,000-dalton proteins. These results suggest that a protein with a molecular weight of 100,000 may either be a precursor or a partially assembled form of other proteins of Complex III, most probably the two largest polypeptides.

Cytochrome b Group↗
PubMed2004

Cytoplasmic localization during testicular biogenesis of the murine mRNA for Spam1 (PH-20), a protein involved in acrosomal exocytosis.

The Sperm Adhesion Molecule1 (SPAM1) is the most widely conserved sperm antigen with important roles in mammalian fertilization. Light and electron microscopy were used to localize, by in situ hybridization, the cellular and subcellular sites of Spam1 mRNA in the murine testis. Transcripts were first detected in step 3 round spermatids, gradually increased until step 8 and abruptly decreased between steps 9-11. They were predominantly localized near the ER and were not dispersed throughout the cytoplasm. Immunohistochemistry revealed that Spam1 is present on both the head and tail of sperm in the seminiferous tubules, and provided support for transcriptional regulation of its transcript. Immunocytochemistry confirmed the location of Spam1 on the tail of testicular sperm and demonstrated that it is localized to both the principal piece and the midpiece. Spam1 on epididymal sperm is localized to the midpiece of the tail and changes from a uniform distribution on the head in the caput to a regionalized pattern, first on the posterior and then on the anterior head, in caudal sperm. Spam1 on the surface of caudal sperm was shown to mediate the increase in acrosome reactions induced by the synergistic effects of HA and progesterone, as confirmed in sperm from the Rb(6.16) translocation-bearing mice which are Spam1 mutants. The similar response of human and mouse sperm to these agonists of the acrosome reaction, underscores the usefulness of the mouse as a model to study physiological aspects of SPAM1 in humans where, unlike the mouse, it is the only sperm hyaluronidase.

Acrosome↗