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Träfflista för sökning "WFRF:(Nilsson IngMarie) srt2:(2000-2004)"

Sökning: WFRF:(Nilsson IngMarie) > (2000-2004)

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1.
  • Mingarro, Ismael, et al. (författare)
  • Different conformations of nascent polypeptides during translocation across the ER membrane
  • 2000
  • Ingår i: BMC Cell Biology. - : Springer Science and Business Media LLC. - 1471-2121. ; 1:3
  • Tidskriftsartikel (refereegranskat)abstract
    • BackgroundIn eukaryotic cells, proteins are translocated across the ER membrane through a continuous ribosome-translocon channel. It is unclear to what extent proteins can fold already within the ribosome-translocon channel, and previous studies suggest that only a limited degree of folding (such as the formation of isolated α-helices) may be possible within the ribosome.ResultsWe have previously shown that the conformation of nascent polypeptide chains in transit through the ribosome-translocon complex can be probed by measuring the number of residues required to span the distance between the ribosomal P-site and the lumenally disposed active site of the oligosaccharyl transferase enzyme (J. Biol. Chem 271: 6241-6244).Using this approach, we now show that model segments composed of residues with strong helix-forming properties in water (Ala, Leu) have a more compact conformation in the ribosome-translocon channel than model segments composed of residues with weak helix-forming potential (Val, Pro).ConclusionsThe main conclusions from the work reported here are (i) that the propensity to form an extended or more compact (possibly α-helical) conformation in the ribosome-translocon channel does not depend on whether or not the model segment has stop-transfer function, but rather seems to reflect the helical propensities of the amino acids as measured in an aqueous environment, and (ii) that stop-transfer sequences may adopt a helical structure and integrate into the ER membrane at different times relative to the time of glycan addition to nearby upstream glycosylation acceptor sites.
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2.
  • Nilsson, IngMarie, et al. (författare)
  • Cleavage of a tail-anchored protein by signal peptidase
  • 2002
  • Ingår i: FEBS Letters. - 0014-5793 .- 1873-3468. ; 516:1-3, s. 106-108
  • Tidskriftsartikel (refereegranskat)abstract
    • Tail-anchored proteins are post-translationally targeted and inserted into the endoplasmic reticulum membrane. They do not use the co-translational sign at-recognition particle (SRP)-dependent pathway, but rather utilize an ill-defined, ATP-dependent mechanism. Here, we show that a tail-anchored protein can be cleaved by signal peptidase and that the sequence requirements for efficient cleavage seem to be the same as for cleavage of co-translationally targeted SRP-dependent proteins.
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3.
  • Nilsson, IngMarie, et al. (författare)
  • Distant downstream sequence determinants can control N-tail translocation during protein insertion into the endoplasmic reticulum membrane
  • 2000
  • Ingår i: Journal of Biological Chemistry. - : Elsevier BV. - 0021-9258 .- 1083-351X. ; 275:9, s. 6207-6213
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied the membrane insertion of ProW, an Escherichia coli inner membrane protein with seven transmembrane segments and a large periplasmic N-terminal tail, into endoplasmic reticulum (ER)-derived dog pancreas microsomes. Strikingly, significant levels of N-tail translocation is seen only when a minimum of four of the transmembrane segments are present; for constructs with fewer transmembrane segments, the N-tail remains mostly nontranslocated and the majority of the molecules adopt an "inverted" topology where normally nontranslocated parts are translocated and vice versa, N-tail translocation can also be promoted by shortening of the N-tail and by the addition of positively charged residues immediately downstream of the first transmembrane segment. We conclude that as many as four consecutive transmembrane segments may be collectively involved in determining membrane protein topology in the ER and that the effects of downstream sequence determinants may vary depending on the size and charge of the N-tail, We also provide evidence to suggest that the ProW N-tail is translocated across the ER membrane in a C-to-N-terminal direction.
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4.
  • Nilsson, IngMarie, et al. (författare)
  • Glycosylation efficiency of Asn-Xaa-Thr sequons depends both on the distance from the C terminus and on the presence of a downstream transmembrane segment
  • 2000
  • Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 275:23, s. 17338-17343
  • Tidskriftsartikel (refereegranskat)abstract
    • Statistical studies of N-glycosylated proteins have indicated that the frequency of nonglycosylated Asn-Xaa-(Thr/Ser) sequons increases toward the C terminus (Gavel, Y., and von Heijne, G. (1990) Protein Eng. 3, 433-442), Using in vitro transcription/translation of a truncated model protein in the presence of dog pancreas microsomes, we find that glycosylation efficiency of Asn-Xaa-Thr sequons indeed is reduced when the sequon is within similar to 60 residues of the C terminus. Surprisingly, the presence of a hydrophobic stop transfer sequence between the Asn-Xaa-Thr sequon and the C terminus results in a very different dependence of glycosylation efficiency on the distance to the C terminus, where the presence of the stop transfer segment inside the ribosome appears to cause a drastic drop in the level of glycosylation. We speculate that this may reflect a change in the structure of the ribosome/translocon complex induced by the stop transfer segment.
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5.
  • Nilsson, IngMarie, et al. (författare)
  • How hydrophobic is alanine?
  • 2003
  • Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 278:32, s. 29389-29393
  • Tidskriftsartikel (refereegranskat)abstract
    • By a number of measures, alanine is poised at the threshold between those amino acids that promote the membrane integration of transmembrane alpha-helices and those that do not. We have measured the preference of alanine to partition into the lipid-water interface region over the central acyl chain region of the endoplasmic reticulum (ER) membrane both by its ability to promote the formation of so-called helical hairpins, i.e. a pair of transmembrane helices separated by a tight turn, and by mapping the position relative to the membrane of the lumenal end of a transmembrane alpha-helix that ends with a block of 10 alanines. Both measures show that Ala has a weak but distinct preference for the interface region, which is in agreement with recent biophysical measurements on pentaeptide partitioning in simple water-lipid or water-octanol systems (Jayasinghe, S., Hristova, K., and White, S. H. ( 2001) J. Mol. Biol. 312, 927 - 934). Considering the complexity of the translocon-mediated insertion of membrane proteins into the ER, the agreement between the biochemical and biophysical measurements is striking and suggests that protein-lipid interactions are already important during the very early steps of membrane protein assembly in the ER.
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6.
  • Nilsson, IngMarie, et al. (författare)
  • Inhibition of protein translocation across the endoplasmic reticulum membrane by sterols
  • 2001
  • Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 276:45, s. 41748-41754
  • Tidskriftsartikel (refereegranskat)abstract
    • Cholesterol and related sterols are known to modulate the physical properties of biological membranes and can affect the activities of membrane-bound protein complexes. Here, we report that an early step in protein translocation across the endoplasmic reticulum (ER) membrane is reversibly inhibited by cholesterol levels significantly lower than those found in the plasma membrane. By UV-induced chemical cross-linking we further show that high cholesterol levels prevent cross-linking between ribosome-nascent chain complexes and components of the Sec61 translocon, but have no effect on cross-linking to the signal recognition particle. The inhibiting effect on translocation is different between different sterols. Our data suggest that the protein translocation machinery may be sensitive to changes in cholesterol levels in the ER membrane.
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7.
  • Nilsson, IngMarie, et al. (författare)
  • Photocross-linking of nascent chains to the STT3 subunit of the oligosaccharyltransferase complex
  • 2003
  • Ingår i: Journal of Cell Biology. - : Rockefeller University Press. - 0021-9525 .- 1540-8140. ; 161:4, s. 715-725
  • Tidskriftsartikel (refereegranskat)abstract
    • In eukaryotic cells, polypeptides are N glycosylated after passing through the membrane of the ER into the ER lumen. This modification is effected cotranslationally by the multimeric oligosaccharyltransferase (OST) enzyme. Here, we report the first cross-linking of an OST subunit to a nascent chain that is undergoing translocation through, or integration into, the ER membrane. A photoreactive probe was incorporated into a nascent chain using a modified Lys-tRNA and was positioned in a cryptic glycosylation site (-Q-K-T- instead of -N-K-T-) in the nascent chain. When translocation intermediates with nascent chains of increasing length were irradiated, nascent chain photocross-linking to translocon components, Sec61alpha and TRAM, was replaced by efficient photocross-linking solely to a protein identified by immunoprecipitation as the STT3 subunit of the OST No cross-linking was observed in the absence of a cryptic sequence or in the presence of a competitive peptide substrate of the OST. As no significant nascent chain photocross-linking to other OST subunits was detected in these fully assembled translocation and integration intermediates, our results strongly indicate that the nascent chain portion of the OST active site is located in STT3.
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