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W Wickner

Publications and source records attributed to W Wickner.

At least 91 records · Page 5Linked to original sources
PubMed1988

Intervacuole exchange in the yeast zygote: a new pathway in organelle communication.

A new pathway of vesicle traffic between organelles has been identified. The vacuoles (lysosomes) of Saccharomyces cerevisiae zygotes rapidly exchange their contents at a specific point in the cell cycle. With the use of fluorescence microscopy, "tracks" were observed that connect the original parental vacuoles to the newly forming bud vacuoles. These observations suggest that vacuole-derived vesicles rapidly move along the tracks in both directions, equilibrating vacuole contents. This rapid vesicle movement may be responsible for vacuole formation in newly developing cells.

Biological Transport↗
PubMed1988

Characterization of the internal signal-anchor domain of Escherichia coli leader peptidase.

Leader peptidase, an integral transmembrane protein of Escherichia coli, is synthesized without a cleavable amino-terminal leader peptide. Of the five domains that participate in the membrane assembly of this protein, one is an internal "signal" region. We have used oligonucleotide-directed mutagenesis to examine the properties of the internal signal that are crucial for leader peptidase assembly. For this purpose, the net charge at the amino terminus of the internal signal was changed from +2 to +1 and -1 and, at the carboxyl terminus of the signal, from 0 to -1 or +1. These mutations had no effect on the membrane assembly of leader peptidase, suggesting that the charges have little role in the signal function. The apolar core of this signal was disrupted by substitution of basic amino acids for apolar residues. Substitution of an arginyl residue at position 70, or two arginyl residues at position 67 and 69, prevented membrane assembly. However, substitution of an arginyl residue at position 66 or either arginyl or lysyl residue at position 68 was without effect. Thus, while the apolar character of the internal signal is important, the precise position of a charged residue determines its effect on assembly.

Endopeptidases↗
PubMed1988

ProOmpA spontaneously folds in a membrane assembly competent state which trigger factor stabilizes.

The precursor protein proOmpA can translocate across purified Escherichia coli inner membrane vesicles in the absence of any other soluble proteins. ProOmpA, purified 2000-fold in the presence of 8 M urea, is competent for translocation following rapid renaturation via dilution. ATP, the transmembrane electrochemical potential, and functional secY protein are essential for the translocation of proOmpA renatured by dilution. The kinetics of its translocation and the level of translocation at each concentration of ATP are indistinguishable from that of proOmpA renatured by dialysis with trigger factor. After dilution, the proOmpA rapidly loses its competence for membrane assembly. However, this competence is stabilized by trigger factor. Assembly-competent proOmpA is in a protease-sensitive conformation, whereas proOmpA which has lost this competence is more resistant to degradation. This suggests that the primary role for trigger factor in in vitro protein translocation is to maintain precursor proteins in a translocation-competent conformation. We propose that a properly folded precursor protein and ATP are the only soluble components which are essential for bacterial protein translocation.

Adenosine Triphosphate↗
PubMed1988

The cytoplasmic domain of Escherichia coli leader peptidase is a "translocation poison" sequence.

Leader peptidase is an integral, transmembrane protein of the plasma membrane of Escherichia coli. Its membrane assembly requires its internal, uncleaved signal sequence, its large periplasmic carboxyl-terminal region, and an apolar domain that is known as a "hydrophobic helper." We now show that the polar cytoplasmic domain of leader peptidase is a unique membrane assembly element, which we term a "translocation poison" sequence. This sequence is defined by its ability to block the action of a signal sequence that either precedes or follows it. To our knowledge, this is the first entirely polar topogenic element. Deletion analysis shows that the role of the leader peptidase hydrophobic helper sequence in its membrane assembly is to overcome the block to assembly caused by the poison sequence.

Cell Membrane↗
PubMed1988

Yeast vacuoles fragment when microtubules are disrupted.

To identify whether microtubules are involved in the maintenance of vacuolar morphology, we treated Saccharomyces cerevisiae with nocodazole and methyl benzimidazole-2-yl-carbamate, drugs which inhibit the polymerization of microtubules. Treated cells arrest with a single large bud in the G2/prophase portion of the cell cycle. Labeling the vacuole with either quinacrine or FITC-dextran revealed vacuole fragmentation that was not found in untreated cells or in cells arrested in G2 by unrelated means. A drug-resistant mutant in beta tubulin does not show vacuolar fragmentation when treated with drug. We propose that microtubules are involved in the regulation of vacuole morphology.

Antifungal Agents↗
PubMed1988

In vitro insertion of leader peptidase into Escherichia coli membrane vesicles.

Leader peptidase is an integral protein of the Escherichia coli cytoplasmic membrane whose topology is known. We have taken advantage of this knowledge and available mutants of this enzyme to develop a genetic test for a cell-free protein translocation reaction. We report that leader peptidase inserted into inverted plasma membrane vesicles in its correct transmembrane orientation. We have examined the in vitro membrane assembly characteristics of a variety of leader peptidase mutants and found that domains required for insertion in vivo are also necessary for insertion in vitro. These data demonstrate the physiological validity of the in vitro insertion reaction and strengthen the use of this in vitro protein translocation reaction for the dissection of this complex sorting pathway.

Cell Membrane↗
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↗
PubMed1987

Leader peptidase of Escherichia coli: critical role of a small domain in membrane assembly.

Leader peptidase spans the Escherichia coli plasma membrane with its amino-terminal domain facing the cytoplasm and its carboxyl terminus facing the periplasm. It is made without a cleavable leader sequence. The three apolar domains near the amino terminus of the peptidase are candidates for internal "signal sequences" and they anchor the protein to the lipid bilayer. Oligonucleotide-directed deletion was used to show that only the second domain has an essential function in membrane assembly. While this second apolar domain is crucial for membrane assembly, its continued function when disrupted by arginine suggests that its apolar character per se is not its only important feature.

Base Sequence↗
PubMed1987

Recombinant forms of M13 procoat with an OmpA leader sequence or a large carboxy-terminal extension retain their independence of secY function.

The assembly of phage M13 procoat protein into the plasma membrane of Escherichia coli is independent of the secY protein. To test whether this is caused by the unusually small size of procoat, we fused DNA encoding 103 amino acids to the carboxy-terminal end of the procoat gene. The resulting fusion protein, which attains the same membrane-spanning conformation as mature coat protein, still does not require the secY function for membrane assembly. To determine whether the leader sequence governs interaction with the secY protein, we genetically exchanged the leader peptides between procoat and pro-OmpA, a protein which does require secY for its membrane assembly. Each of the resulting hybrid proteins assembles across the plasma membrane, though at a reduced rate. Membrane assembly of the fusion of procoat leader and OmpA required secY function, whereas assembly of the pro-OmpA leader/coat protein fusion was independent of secY. Properties of the entire procoat molecule, rather than its small size or a specific property of its leader peptide determines its mode of membrane assembly.

Bacterial Outer Membrane Proteins↗
PubMed1987

Trigger factor: a soluble protein that folds pro-OmpA into a membrane-assembly-competent form.

Pro-OmpA that is synthesized in vitro can assemble into bacterial inner membrane vesicles in the presence of ATP and NADH. We have purified pro-OmpA to determine which additional soluble proteins are necessary for its membrane assembly. [35S]Pro-OmpA was bound to Sepharose-linked antibody to OmpA, then eluted with 8 M urea and chromatographed on an anion-exchange resin in 8 M urea. This pro-OmpA is purified 2000-fold and is radiochemically pure. After dialysis, it is soluble but incompetent for membrane assembly. Addition of an Escherichia coli cytoplasmic fraction (S100) to the assembly reaction does not allow translocation. However, when S100 is added to pro-OmpA prior to dialysis, full assembly competence is restored, suggesting that a soluble factor, termed "trigger factor," triggers the folding of pro-OmpA into an assembly-competent form as the urea is removed. We noted that, prior to the last purification step, the immunoaffinity-purified pro-OmpA was partially competent for membrane assembly without addition of trigger factor. To test whether trigger factor had bound to the antibody column by means of its association with pro-OmpA, the crude pro-OmpA was acid-denatured prior to immunoadsorption. In this experiment, the trigger factor did not bind to the anti-OmpA column, and S100 was required for renaturation of this [35S]pro-OmpA. As suggested by this experiment, the crude [35S]pro-OmpA was in a complex with other proteins. Sedimentation velocity studies showed that the trigger factor has an apparent molecular weight of approximately 60,000. We propose that it is required for translocation-competent folding of pro-OmpA and other precursor proteins.

Adenosine Triphosphate↗
PubMed1987

Multiple methods of visualizing the yeast vacuole permit evaluation of its morphology and inheritance during the cell cycle.

The vacuole of the yeast Saccharomyces cerevisiae was visualized with three unrelated fluorescent dyes: FITC-dextran, quinacrine, and an endogenous fluorophore produced in ade2 yeast. FITC-dextran, which enters cells by endocytosis, had been previously developed as a vital stain for yeast vacuoles. Quinacrine, which diffuses across membranes and accumulates in acidic compartments in mammalian cells, can also be used as a marker for yeast vacuoles. ade2 yeast accumulate an endogenous fluorophore in their vacuoles. Using these stains, yeast were examined for vacuole morphology throughout the cell division cycle. In both the parent cell and the bud, a single vacuole was the most common morphology at every stage. Two or more vacuoles could also be found in the mother cell or in the bud; however, this morphology was not correlated with any stage of the cell division cycle. Even small buds (in early S phase) often contained a small vacuole. By the time the bud was half the diameter of the mother cell, it almost always bore a vacuole. This picture of vacuole division and segregation differs from what is seen with synchronized cultures. In ade2 yeast, the bud usually inherits a substantial portion of its vacuole contents from the mother cell. We propose that vacuolar segregation is accomplished by vesicular traffic between the parent cell and the bud.

Cell Cycle↗
PubMed1986

Both hydrophobic domains of M13 procoat are required to initiate membrane insertion.

M13 procoat protein has two hydrophobic domains, one in the leader peptide and one which anchors the mature coat protein in the membrane. Disruption of the membrane anchor region by insertion of arginyl residues does not yield periplasmic coat protein. Instead, the rate of membrane assembly is slowed greater than 100-fold (t1/2 less than 5 s for wild-type, t1/2 greater than 10 min for mutant). The hydrophobic region of mature coat protein not only functions as a membrane anchor, but has an important role in the membrane assembly process per se.

Amino Acid Sequence↗
PubMed1986

The role of the polar, carboxyl-terminal domain of Escherichia coli leader peptidase in its translocation across the plasma membrane.

Leader peptidase, an integral membrane protein of Escherichia coli, is made without a cleavable leader sequence. It has 323 amino acid residues and spans the plasma membrane with a small amino-terminal domain exposed to the cytoplasm and a large, carboxyl-terminal domain exposed to the periplasm. We have investigated which regions of leader peptidase are necessary for its assembly across the membrane. Deletions were made in the carboxyl-terminal domain of leader peptidase, removing residues 141-222, 142-323, or 222-323. Protease accessibility was used to determine whether the polar, carboxyl-terminal domains of these truncated leader peptidases were translocated across the membrane. The removal of either residues 222-323 (the extreme carboxyl terminus) or residues 141-222 does not prevent leader peptidase membrane assembly. However, leader peptidase lacking both regions, i.e. amino acid residues 142-323, cannot translocate the remaining portion of its carboxyl terminus across the membrane. Our data suggest that the polar, periplasmic domain of leader peptidase contains information which is needed for membrane assembly.

Amino Acid Sequence↗
PubMed1986

The secY protein can act post-translationally to promote bacterial protein export.

Conditionally lethal Escherichia coli mutants in secY (prlA) show defective export of proteins to the periplasm and outer membrane. It has been proposed that this gene and other sec genes must act on pro-OmpA at an early stage of protein synthesis in order to allow later translocation to occur. We have described a temperature-sensitive mutation in which the secYts function is impaired at the nonpermissive temperature (Ito, K. (1984) Mol. Gen. Genet. 197, 204-208). A plasmid bearing the wild-type secY gene under the control of the lactose operon (Shiba, K., Ito, K., Yura, T., and Cerretti, D. P. (1984) EMBO J. 3, 631-635) has been introduced into this mutant strain. We now report that the in vivo chase of pulse-labeled full length pro-OmpA to mature OmpA is accelerated by inducing the synthesis of the wild-type secY protein at the end of the period of pulse labeling. We have also assayed the requirements for secY function for in vitro protein translocation. Membranes derived from secY ts cells which were incubated at 42 degrees C were inactive in vitro in the post-translational uptake and processing of pro-OmpA. Thus, the secY protein can act post-translationally, enhancing the translocation of completed pro-OmpA polypeptide chains across the plasma membrane.

Bacterial Proteins↗
PubMed1986

Requirements for substrate recognition by bacterial leader peptidase.

Many secreted and membrane proteins have amino-terminal leader peptides which are essential for their insertion across the membrane bilayer. These precursor proteins, whether from prokaryotic or eukaryotic sources, can be processed to their mature forms in vitro by bacterial leader peptidase. While different leader peptides have shared features, they do not share a unique sequence at the cleavage site. To examine the requirements for substrate recognition by leader peptidase, we have truncated M13 procoat, a membrane protein precursor, from both the amino- and carboxy-terminal ends with specific proteases or chemical cleavage agents. The fragments isolated from these reactions were assayed as substrates for leader peptidase. A 16 amino acid residue peptide which spans the leader peptidase cleavage site is accurately cleaved. Neither the basic amino-terminal region nor most of the hydrophobic central region of the leader peptide are essential for accurate cleavage.

Amino Acid Sequence↗
PubMed1986

Both ATP and the electrochemical potential are required for optimal assembly of pro-OmpA into Escherichia coli inner membrane vesicles.

Pro-OmpA is processed to OmpA by isolated inverted plasma membrane vesicles from Escherichia coli. In the presence of ATP and a membrane potential, 58% (+/- 13%) of the OmpA is sequestered in the vesicles. We sought to determine which of these two metabolic energy sources is used for protein translocation. The plasma membrane F1F0-ATPase is the central enzyme that interconverts the energy of membrane electrochemical potential and ATP. To separate the effects of these two forms of energy in vitro, the ATPase was inactivated, either by "stripping" the F1 from the membranes with low salt and EDTA or by using membrane vesicles derived from a strain without the atp operon. In each case, optimal translocation and processing of pro-OmpA required both a membrane potential and ATP. We conclude that ATP and membrane potential are separate requirements for bacterial protein export.

Adenosine Triphosphate↗