scholarly journals C-terminal sequences can inhibit the insertion of membrane proteins into the endoplasmic reticulum of Saccharomyces cerevisiae.

1992 ◽  
Vol 12 (1) ◽  
pp. 276-282 ◽  
Author(s):  
N Green ◽  
P Walter
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Fusion Proteins ◽  
Signal Sequence ◽  
Dna Encoding ◽  
Luminal Side ◽  
Internal Signal ◽  
Histidinol Dehydrogenase ◽  
Arginine Permease ◽  
Er Membrane

We have constructed three gene fusions that encode portions of a membrane protein, arginine permease, fused to a reporter domain, the cytoplasmic enzyme histidinol dehydrogenase (HD), located at the C-terminal end. These fusion proteins contain at least one of the internal signal sequences of arginine permease. When the fusion proteins were expressed in Saccharomyces cerevisiae and inserted into the endoplasmic reticulum (ER), two of the fusion proteins placed HD on the luminal side of the ER membrane, but only when a piece of DNA encoding a spacer protein segment was inserted into the fusion joint. The third fusion protein, with or without the spacer included, placed HD on the cytoplasmic side of the membrane. These results suggest that (i) sequences C-terminal to the internal signal sequence can inhibit membrane insertion and (ii) HD requires a preceding spacer segment to be translocated across the ER membrane.

C-terminal sequences can inhibit the insertion of membrane proteins into the endoplasmic reticulum of Saccharomyces cerevisiae

1992 ◽  
Vol 12 (1) ◽  
pp. 276-282
Author(s):  
N Green ◽  
P Walter
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Fusion Proteins ◽  
Signal Sequence ◽  
Dna Encoding ◽  
Luminal Side ◽  
Internal Signal ◽  
Histidinol Dehydrogenase ◽  
Arginine Permease ◽  
Er Membrane

We have constructed three gene fusions that encode portions of a membrane protein, arginine permease, fused to a reporter domain, the cytoplasmic enzyme histidinol dehydrogenase (HD), located at the C-terminal end. These fusion proteins contain at least one of the internal signal sequences of arginine permease. When the fusion proteins were expressed in Saccharomyces cerevisiae and inserted into the endoplasmic reticulum (ER), two of the fusion proteins placed HD on the luminal side of the ER membrane, but only when a piece of DNA encoding a spacer protein segment was inserted into the fusion joint. The third fusion protein, with or without the spacer included, placed HD on the cytoplasmic side of the membrane. These results suggest that (i) sequences C-terminal to the internal signal sequence can inhibit membrane insertion and (ii) HD requires a preceding spacer segment to be translocated across the ER membrane.

Efficiency and diversity of protein localization by random signal sequences

1990 ◽  
Vol 10 (6) ◽  
pp. 3163-3173
Author(s):  
C A Kaiser ◽  
D Botstein
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Signal Peptide ◽  
Signal Sequence ◽  
Protein Localization ◽  
Random Signal ◽  
Perinuclear Region ◽  
Hybrid Protein ◽  
Random Sequences ◽  
Beta Galactosidase

Three randomly derived sequences that can substitute for the signal peptide of Saccharomyces cerevisiae invertase were tested for the efficiency with which they can translocate invertase or beta-galactosidase into the endoplasmic reticulum. The rate of translocation, as measured by glycosylation, was estimated in pulse-chase experiments to be less than 6 min. When fused to beta-galactosidase, these peptides, like the normal invertase signal sequence, direct the hybrid protein to a perinuclear region, consistent with localization to the endoplasmic reticulum. The diversity of function of random peptides was studied further by immunofluorescence localization of proteins fused to 28 random sequences: 4 directed the hybrid to the endoplasmic reticulum, 3 directed it to the mitochondria, and 1 directed it to the nucleus.

scholarly journals Different subcellular localization of Saccharomyces cerevisiae HMG-CoA reductase isozymes at elevated levels corresponds to distinct endoplasmic reticulum membrane proliferations.

1996 ◽  
Vol 7 (5) ◽  
pp. 769-789 ◽  
Author(s):  
A J Koning ◽  
C J Roberts ◽  
R L Wright
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Subcellular Localization ◽  
Nuclear Envelope ◽  
Fluorescent Protein ◽  
Endoplasmic Reticulum Membrane ◽  
Hmg Coa Reductase ◽  
Endogenous Expression ◽  
Coa Reductase ◽  
Er Membrane

In all eucaryotic cell types analyzed, proliferations of the endoplasmic reticulum (ER) can be induced by increasing the levels of certain integral ER proteins. One of the best characterized of these proteins is HMG-CoA reductase, which catalyzes the rate-limiting step in sterol biosynthesis. We have investigated the subcellular distributions of the two HMG-CoA reductase isozymes in Saccharomyces cerevisiae and the types of ER proliferations that arise in response to elevated levels of each isozyme. At endogenous expression levels, Hmg1p and Hmg2p were both primarily localized in the nuclear envelope. However, at increased levels, the isozymes displayed distinct subcellular localization patterns in which each isozyme was predominantly localized in a different region of the ER. Specifically, increased levels of Hmg1p were concentrated in the nuclear envelope, whereas increased levels of Hmg2p were concentrated in the peripheral ER. In addition, an Hmg2p chimeric protein containing a 77-amino acid lumenal segment from Hmg1p was localized in a pattern that resembled that of Hmg1p when expressed at increased levels. Reflecting their different subcellular distributions, elevated levels of Hmg1p and Hmg2p induced sets of ER membrane proliferations with distinct morphologies. The ER membrane protein, Sec61p, was localized in the membranes induced by both Hmg1p and Hmg2p green fluorescent protein (GFP) fusions. In contrast, the lumenal ER protein, Kar2p, was present in Hmg1p:GFP membranes, but only rarely in Hmg2p:GFP membranes. These results indicated that the membranes synthesized in response to Hmg1p and Hmg2p were derived from the ER, but that the membranes were not identical in protein composition. We determined that the different types of ER proliferations were not simply due to quantitative differences in protein amounts or to the different half-lives of the two isozymes. It is possible that the specific distributions of the two yeast HMG-CoA reductase isozymes and their corresponding membrane proliferations may reveal regions of the ER that are specialized for certain branches of the sterol biosynthetic pathway.

Genetic and biochemical evaluation of eucaryotic membrane protein topology: multiple transmembrane domains of Saccharomyces cerevisiae 3-hydroxy-3-methylglutaryl coenzyme A reductase

1990 ◽  
Vol 10 (2) ◽  
pp. 672-680
Author(s):  
C Sengstag ◽  
C Stirling ◽  
R Schekman ◽  
J Rine
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Coenzyme A ◽  
Transmembrane Domains ◽  
Protein Domain ◽  
Yeast Cells ◽  
Endoplasmic Reticulum Membrane ◽  
Hmg Coa Reductase ◽  
Coa Reductase ◽  
Histidinol Dehydrogenase

Both 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase isozymes of the yeast Saccharomyces cerevisiae are predicted to contain seven membrane-spanning domains. Previous work had established the utility of the histidinol dehydrogenase protein domain, encoded by HIS4C, as a topologically sensitive monitor that can be used to distinguish between the lumen of the endoplasmic reticulum and the cytoplasm. This study directly tested the structural predictions for HMG-CoA reductase by fusing the HIS4C domain to specific sites in the HMG-CoA reductase isozymes. Yeast cells containing the HMG-CoA reductase-histidinol dehydrogenase fusion proteins grew on histidinol-containing medium if the HIS4C domain was present on the cytoplasmic side of the endoplasmic reticulum membrane but not if the HIS4C domain was targeted to the endoplasmic reticulum lumen. Systematic exchanges of transmembrane domains between the isozymes confirmed that both isozymes had equivalent membrane topologies. In general, deletion of an even number of putative transmembrane domains did not interfere with the topology of the protein, but deletion or duplication of an odd number of transmembrane domains inverted the orientation of the protein. The data confirmed the earlier proposed topology for yeast HMG-CoA reductase, demonstrated that the yeast enzymes are core glycosylated, and provided in vivo evidence that the properties of transmembrane domains were, in part, dependent upon their context within the protein.

scholarly journals Structural requirements for intracellular targeting of SP-C proprotein

1999 ◽  
Vol 277 (5) ◽  
pp. L1034-L1044 ◽  
Author(s):  
Scott J. Russo ◽  
Wenjing Wang ◽  
Catherine A. Lomax ◽  
Michael F. Beers
Keyword(s):  
Endoplasmic Reticulum ◽  
Amino Acid ◽  
Fusion Proteins ◽  
Fluorescent Protein ◽  
Signal Sequence ◽  
Expression Patterns ◽  
A549 Cells ◽  
Surfactant Protein ◽  
Lung Epithelial Cells ◽  
Golgi Compartment

Rat surfactant protein (SP) C is synthesized as a 194-amino acid proprotein that is proteolytically processed to a 35-amino acid mature form in subcellular compartments distal to the medial Golgi compartment. To identify domains of SP-C proprotein (proSP-C) necessary for endoplasmic reticulum translocation and for targeting to cytosolic processing compartments, we characterized expression patterns of heterologous SP-C fusion proteins in A549 lung epithelial cells and in the rat pheochromocytoma cell line PC-12. cDNA constructs were produced; these constructs encoded fusion proteins consisting of enhanced green fluorescent protein (EGFP) and wild-type proSP-C (EGFP/SP-C1–194), mature SP-C (EGFP/SP-C24–59), or progressive deletions of the NH2- or COOH-terminal flanking domains. By fluorescence microscopy, EGFP/SP-C1–194transfected into A549 cells was translocated and expressed in acidic cytoplasmic vesicles. By deletional analysis, a functional signal peptide was mapped to the domain Phe24 to His59, whereas a motif for targeting to cytosolic vesicular compartments was localized to the NH2 flanking domain Met10 to Gln23. Truncations of the distal COOH terminus were retained in the endoplasmic reticulum/Golgi compartment; however, the COOH flanking region alone was insufficient for targeting. In PC-12 cells, EGFP/SP-C1–194 was expressed in peripheral cytosolic vesicles, whereas EGFP/SP-C24–194 and EGFP/SP-C24–59 were each translocated but not targeted. We conclude that two domains in the proSP-C sequence are required for targeting: mature SP-C (Phe24 to Leu58) contains a functional signal sequence active in epithelial and nonepithelial cells, whereas Met10 to Gln23, but not the COOH flanking peptide, is required for targeting to late vesicular compartments.

scholarly journals Recognition of a Subset of Signal Sequences by Ssh1p, a Sec61p-related Protein in the Membrane of Endoplasmic Reticulum of Yeast Saccharomyces cerevisiae

2002 ◽  
Vol 13 (7) ◽  
pp. 2223-2232 ◽  
Author(s):  
Sandra Wittke ◽  
Martin Dünnwald ◽  
Markus Albertsen ◽  
Nils Johnsson
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Signal Sequence ◽  
Carboxypeptidase Y ◽  
Related Protein ◽  
Signal Sequences ◽  
Yeast Saccharomyces Cerevisiae ◽  
Sequence Recognition ◽  
Split Ubiquitin

Ssh1p of Saccharomyces cerevisiae is related in sequence to Sec61p, a general receptor for signal sequences and the major subunit of the channel that guides proteins across the membrane of the endoplasmic reticulum. The split-ubiquitin technique was used to determine whether Ssh1p serves as an additional receptor for signal sequences in vivo. We measured the interactions between the Nub-labeled Ssh1p and Cub-translocation substrates bearing four different signal sequences. The so-determined interaction profile of Ssh1p was compared with the signal sequence interaction profile of the correspondingly modified Nub-Sec61p. The assay reveals interactions of Ssh1p with the signal sequences of Kar2p and invertase, whereas Sec61p additionally interacts with the signal sequences of Mfα1 and carboxypeptidase Y. The measured physical proximity between Ssh1p and the β-subunit of the signal sequence recognition particle receptor confirms our hypothesis that Ssh1p is directly involved in the cotranslational translocation of proteins across the membrane of the endoplasmic reticulum.

scholarly journals The liver isoform of carnitine palmitoyltransferase 1 is not targeted to the endoplasmic reticulum

2003 ◽  
Vol 370 (1) ◽  
pp. 223-231 ◽  
Author(s):  
Neil M. BROADWAY ◽  
Richard J. PEASE ◽  
Graeme BIRDSEY ◽  
Majid SHAYEGHI ◽  
Nigel A. TURNER ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Fusion Protein ◽  
Fluorescent Protein ◽  
Signal Sequence ◽  
Gradient Centrifugation ◽  
Carnitine Palmitoyltransferase ◽  
Membrane Contact Sites ◽  
Malonyl Coa ◽  
Carnitine Palmitoyltransferase 1 ◽  
Er Membrane

Liver microsomal fractions contain a malonyl-CoA-inhibitable carnitine acyltransferase (CAT) activity. It has been proposed [Fraser, Corstorphine, Price and Zammit (1999) FEBS Lett. 446, 69—74] that this microsomal CAT activity is due to the liver form of carnitine palmitoyltransferase 1 (L-CPT1) being targeted to the endoplasmic reticulum (ER) membrane as well as to mitochondria, possibly by an N-terminal signal sequence [Cohen, Guillerault, Girard and Prip-Buus (2001) J. Biol. Chem. 276, 5403—5411]. COS-1 cells were transiently transfected to express a fusion protein in which enhanced green fluorescent protein was fused to the C-terminus of L-CPT1. Confocal microscopy showed that this fusion protein was localized to mitochondria, and possibly to peroxisomes, but not to the ER. cDNAs corresponding to truncated (amino acids 1—328) or full-length L-CPT1 were transcribed and translated in the presence of canine pancreatic microsomes. However, there was no evidence of authentic insertion of CPT1 into the ER membrane. Rat liver microsomal fractions purified by sucrose-density-gradient centrifugation contained an 88kDa protein (p88) which was recognized by an anti-L-CPT1 antibody and by 2,4-dinitrophenol-etomoxiryl-CoA, a covalent inhibitor of L-CPT1. Abundance of p88 and malonyl-CoA-inhibitable CAT activity were increased approx. 3-fold by starvation for 24h. Deoxycholate solubilized p88 and malonyl-CoA-inhibitable CAT activity from microsomes to approximately the same extent. The microsomal fraction contained porin, which, relative to total protein, was as abundant as in crude mitochondrial outer membranes fractions. It is concluded that L-CPT1 is not targeted to the ER membrane and that malonyl-CoA CAT in microsomal fractions is L-CPT1 that is derived from mitochondria, possibly from membrane contact sites.

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