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At least 127 records · Page 7Linked to original sources
PubMed1990

Degradation of proteins by the ubiquitin-mediated proteolytic pathway.

Degradation of a protein by the ubiquitin system involves two distinct processes. In the first step, ubiquitin is covalently linked in an ATP-dependent mode to the protein substrate. The protein moiety of the conjugate is then degraded by a specific protease into free amino acids, resulting in the release of free and reutilizable ubiquitin. This process also requires energy. In this review we will briefly summarize our current knowledge of the role of the ubiquitin system in protein turnover and discuss in detail the mechanism involved in selection of substrates for conjugation and in degradation of ubiquitin-conjugated proteins.

Adenosine Triphosphate↗
PubMedDate not supplied

[Co-translation folding, compartmentalization and modification of proteins].

Transmembrane transport of polypeptide chains in the process of their synthesis on membrane-bound ribosomes and enzymic modification of the nascent polypeptides on membranes are reviewed. The possible role of ribosomes in protein folding and some other unsolved problems are discussed.

Amino Acid Sequence↗
PubMed1992

Tyrosine kinases and their interactions with signalling proteins.

Recent progress has been made in identifying signal transduction pathways controlled by receptor protein-tyrosine kinases. The receptors for nerve growth factor and hepatocyte growth factor have been identified as the Trk and Met tyrosine kinases. The stimulation of intracellular signal transduction pathways by activated receptors appears to involve the association of SH2-containing cytoplasmic signalling proteins with autophosphorylated receptors.

Animals↗
PubMed1989

The degradation signal in a short-lived protein.

Our previous work has shown that the amino-terminal residue of a short-lived protein is a distinct component of the protein's degradation signal. To define the complete signal, otherwise identical dihydrofolate reductase test proteins bearing different extensions and either a "stabilizing" or a "destabilizing" amino-terminal residue were expressed in the yeast S. cerevisiae and their in vivo half-lives compared. The amino-terminal degradation signal is shown to comprise two distinct determinants. One, discovered previously, is the protein's amino-terminal residue. The second determinant, identified in the present work, is a specific lysine residue whose function in the degradation signal is not dependent on the unique amino acid sequences in the vicinity of the residue. The mechanistic significance of the second determinant is illuminated by the finding that in a targeted, short-lived protein, a chain of branched ubiquitin-ubiquitin conjugates is confined to a lysine residue that has been identified in the present work as the second determinant of the degradation signal.

Amino Acid Sequence↗
PubMed1992

Characterization of the secretion efficiency of a plant signal peptide in Bacillus subtilis.

The ability of the Bacillus subtilis secretion machinery to interact with a heterologous signal peptide was studied using a plant (wheat alpha-amylase) signal peptide. The plant signal peptide was capable of mediating secretion of Escherichia coli alkaline phosphatase and B. amyloliquefaciens levansucrase from B. subtilis. This secretion was dependent on the plant signal peptide, as deletion of five amino acids from the hydrophobic core resulted in a block of secretion. Attempts to improve the efficiency of the plant signal peptide in B. subtilis were made by increasing the length of the hydrophobic core from 10 to 16 residues by insertion of 2, 4, 5 or 6 amino acids. None of the alterations improved the secretion efficiency relative to the wild-type plant signal peptide.

Alkaline Phosphatase↗
PubMedDate not supplied

[A method for determining the classification of a protein in a given family at a low level of similarity].

Basing on the analysis of the primary structure of proteins from a family of signal receptor proteins, the existence of short extremely conservative family-specific chains was postulated. These chains may serve as a marker in determination of the relationship of a protein to the given family. On the basis of the performed analysis, it is suggested that mass-oncogene belongs to the family of signal receptors, whereas pheromonal receptor of the yeasts STE-2--presumably does not.

Amino Acid Sequence↗
PubMed1990

src-related tyrosine protein kinases as signaling components in hematopoietic cells.

The src-related tyrosine protein kinases are thought to be involved in the transduction of signals controlling cell growth as well as in specialized functions in fully differentiated, nonproliferating cells. The association of one of these kinases, p56lck, with the CD4 and CD8 cell-surface receptors in T lymphocytes has provided a model system through which the first function for a src-related tyrosine kinase has been defined. These initial observations in T lymphocytes have led investigators to explore the potential association of the src-related tyrosine kinases with other receptor complexes. Evidence that these kinases may be involved in mediating signaling events through such diverse cellular receptors as those found in B lymphocytes and basophils is currently being pursued.

Animals↗
PubMed1992

Accumulation of alkaliphilic Bacillus penicillinase cleaved within the signal sequence in cytoplasm of Escherichia coli.

Alkaliphilic Bacillus penicillinase produced by Escherichia coli is distributed in several subcellular compartments according to cultivation conditions. The penicillinase that accumulated in particular subcellular fractions of E. coli grown under different conditions was purified and characterized. Periplasmic or extracellular penicillinase (24 kDa) was mature protein, indicating that the putative precursor (27 kDa) was processed at the correct amino acid residue, probably by signal peptidase I. Cytoplasmic penicillinase contained two unusual proteins (25 kDa) that are produced by proteolytic cleavage of the precursor within its signal sequence.

Amino Acid Sequence↗
PubMed1987

The internal signal sequence of Escherichia coli leader peptidase is necessary, but not sufficient, for its rapid membrane assembly.

Leader peptidase of Escherichia coli, a protein of 323 residues, has three hydrophobic domains. The first, residues 1-22, is the most apolar and is followed by a polar region (23-61) which faces the cytoplasm. The second hydrophobic domain (residues 62-76) spans the membrane. The third hydrophobic domain, which has a minimal apolar character, and the polar, carboxyl-terminal two-thirds of the protein are exposed to the periplasm. Deletion of either the amino terminus (residues 4-50) or the third hydrophobic region (residues 83-98) has almost no effect on the rate of leader peptidase membrane assembly, while the second hydrophobic domain is essential for insertion (Dalbey, R., and Wickner, W. (1987) Science 235, 783-787). To further define the roles of these domains, we have replaced the normal, cleaved leader sequence of pro-OmpA and M13 procoat with regions containing either the first or second apolar domain of leader peptidase. The second apolar domain supports the translocation of OmpA or coat protein across the plasma membrane, establishing its identity as an internal, uncleaved signal sequence. In addition to this sequence, we now find that leader peptidase needs either the amino-terminal domain or the third hydrophobic domain to permit its rapid membrane assembly. These results show that, although a signal sequence is necessary for rapid membrane assembly of leader peptidase, it is not sufficient.

Base Sequence↗
PubMed1985

Dual functions of the signal peptide in protein transfer across the membrane.

Most secretory proteins in both prokaryotic and eukaryotic cells are synthesized from a precursor with an amino-terminal extension of 20 to 25 amino acid residues called a signal peptide. These signal peptides are removed during translocation of the secretory proteins across the membrane. When two precursor structures are fused, the internalized second signal peptide was found to exert two different roles, depending upon either the distance between the two signal peptides, or whether the first signal peptide functions cotranslationally or posttranslationally. One role is to function as the usual signal peptide to translocate the protein downstream of the internal signal peptide. The other role is to function as a stop-transfer signal to create a transmembrane protein with the second signal peptide anchoring the protein in the membrane.

Bacterial Outer Membrane Proteins↗
PubMed1989

Processing and secretion of barley (1-3,1-4)-beta-glucanase in yeast.

DNA segments encoding signal peptides from mouse alpha-amylase, yeast acid phosphatase, and yeast invertase were fused in frame to a barley (1-3,1-4)-beta-glucanase cDNA gene and expressed in yeast cells under the control of the phosphoglycerate kinase gene promoter. Pure beta-glucanase is obtained by gel filtration of concentrated yeast cell supernatant. It was shown that the glucanase pre-protein was specifically processed and the mature protein efficiently secreted when the yeast invertase signal sequence directed secretion.

Acid Phosphatase↗
PubMedDate not supplied

[Construction of plasmids coding for diphtheria toxin fragments].

Plasmids coding different nontoxic derivatives (toxoids) of the diphtheria toxin were constructed. A secretion of toxoids that carry a signal sequence was found in the periplasmic space of E. coli and Erwinia carotovora. Toxoids without a signal sequence appear in the cytoplasm. We believe that the toxoids secreted in E. coli and E. carotovora cells undergo a limited proteolysis. According to the molecular weights of the fragments there are three targets for proteolysis. One of them being just between A- and B-fragments of the diphtheria toxin. The others are localised in the B-fragment. The role of E. coli signal peptidase in the specific cutting is discussed.

Amino Acid Sequence↗