| 1. |
- Jaud, Simon, et al.
(författare)
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Insertion of short transmembrane helices by the Sec61 translocon
- 2009
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 106:28, s. 11588-11593
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Tidskriftsartikel (refereegranskat)abstract
- The insertion efficiency of transmembrane (TM) helices by the Sec61 translocon depends on helix amino acid composition, the positions of the amino acids within the helix, and helix length. We have used an in vitro expression system to examine systematically the insertion efficiency of short polyleucine segments (L(n), n = 4 ... 12) flanked at either end by 4-residue sequences of the form XXPX-L(n)-XPXX with X = G, N, D, or K. Except for X = K, insertion efficiency (p) is <10% for n < 8, but rises steeply to 100% for n = 12. For X = K, p is already close to 100% for n = 10. A similar pattern is observed for synthetic peptides incorporated into oriented phospholipid bilayer arrays, consistent with the idea that recognition of TM segments by the translocon critically involves physical partitioning of nascent peptide chains into the lipid bilayer. Molecular dynamics simulations suggest that insertion efficiency is determined primarily by the energetic cost of distorting the bilayer in the vicinity of the TM helix. Very short lysine-flanked leucine segments can reduce the energetic cost by extensive hydrogen bonding with water and lipid phosphate groups (snorkeling) and by partial unfolding.
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| 2. |
- Ismail, Nurzian, et al.
(författare)
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Charge-driven dynamics of nascent-chain movement through the SecYEG translocon
- 2015
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Ingår i: Nature Structural & Molecular Biology. - : Springer Science and Business Media LLC. - 1545-9993 .- 1545-9985. ; 22:2, s. 145-149
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Tidskriftsartikel (refereegranskat)abstract
- On average, every fifth residue in secretory proteins carries either a positive or a negative charge. In a bacterium such as Escherichia coli, charged residues are exposed to an electric field as they transit through the inner membrane, and this should generate a fluctuating electric force on a translocating nascent chain. Here, we have used translational arrest peptides as in vivo force sensors to measure this electric force during cotranslational chain translocation through the SecYEG translocon. We find that charged residues experience a biphasic electric force as they move across the membrane, including an early component with a maximum when they are 47-49 residues away from the ribosomal P site, followed by a more slowly varying component. The early component is generated by the transmembrane electric potential, whereas the second may reflect interactions between charged residues and the periplasmic membrane surface.
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| 3. |
- Contreras, F.-Xabier, et al.
(författare)
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Molecular recognition of a single sphingolipid species by a protein's transmembrane domain
- 2012
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 481:7382, s. 525-529
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Tidskriftsartikel (refereegranskat)abstract
- Functioning and processing of membrane proteins critically depend on the way their transmembrane segments are embedded in the membrane. Sphingolipids are structural components of membranes and can also act as intracellular second messengers. Not much is known of sphingolipids binding to transmembrane domains (TMDs) of proteins within the hydrophobic bilayer, and how this could affect protein function. Here we show a direct and highly specific interaction of exclusively one sphingomyelin species, SM 18, with the TMD of the COPI machinery protein p24 (ref. 2). Strikingly, the interaction depends on both the headgroup and the backbone of the sphingolipid, and on a signature sequence (VXXTLXXIY) within the TMD. Molecular dynamics simulations show a close interaction of SM 18 with the TMD. We suggest a role of SM 18 in regulating the equilibrium between an inactive monomeric and an active oligomeric state of the p24 protein, which in turn regulates COPI-dependent transport. Bioinformatic analyses predict that the signature sequence represents a conserved sphingolipid-binding cavity in a variety of mammalian membrane proteins. Thus, in addition to a function as second messengers, sphingolipids can act as cofactors to regulate the function of transmembrane proteins. Our discovery of an unprecedented specificity of interaction of a TMD with an individual sphingolipid species adds to our understanding of why biological membranes are assembled from such a large variety of different lipids.
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| 4. |
- Nørholm, Morten H. H., et al.
(författare)
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Manipulating the genetic code for membrane protein production : What have we learnt so far?
- 2012
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2736. ; 1818:4, s. 1091-1096
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Forskningsöversikt (refereegranskat)abstract
- With synthetic gene services, molecular cloning is as easy as ordering a pizza. However choosing the right RNA code for efficient protein production is less straightforward, more akin to deciding on the pizza toppings. The possibility to choose synonymous codons in the gene sequence has ignited a discussion that dates back 50years: Does synonymous codon use matter? Recent studies indicate that replacement of particular codons for synonymous codons can improve expression in homologous or heterologous hosts, however it is not always successful. Furthermore it is increasingly apparent that membrane protein biogenesis can be codon-sensitive. Single synonymous codon substitutions can influence mRNA stability, mRNA structure, translational initiation, translational elongation and even protein folding. Synonymous codon substitutions therefore need to be carefully evaluated when membrane proteins are engineered for higher production levels and further studies are needed to fully understand how to select the codons that are optimal for higher production. This article is part of a Special Issue entitled: Protein Folding in Membranes.
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| 5. |
- Hedman, Rickard, 1983-
(författare)
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Dynamics of peptide chains during co-translational translocation, membrane integration & domain folding
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The biosynthesis of proteins occurs at the ribosomes, where amino acids are linked together into linear chains. Nascent protein chains may undergo several different processes during their synthesis. Some proteins begin to fold, while others interact with chaperones, targeting factors or processing enzymes. Nascent membrane proteins are targeted to the cell membrane for integration, which involves the translocation of periplasmic domains and the insertion of membrane-embedded parts.The aim of this thesis was to gain insights about the dynamics of nascent peptide chains undergoing folding, membrane translocation and integration. To this end, we explored the use of arrest peptides (APs) as force sensors. APs stall ribosomes when translated unless there is tension in the nascent peptide chain: the higher the tension, the more full-length protein can be detected. By using APs, we could show that a transmembrane helix is strongly ‘pulled’ twice on its way into the membrane and that strong electric forces act on negatively charged peptide segments translocating through the membrane. Furthermore, we discovered that APs could be used to detect protein folding and made the surprising discovery that a small protein domain folded well inside the ribosomal tunnel. Finally, we explored the arrest-stability of a large set of AP variants and found two extremely stable APs.
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| 6. |
- Nilsson, Ola B., et al.
(författare)
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Cotranslational Protein Folding inside the Ribosome Exit Tunnel
- 2015
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Ingår i: Cell Reports. - : Elsevier BV. - 2211-1247. ; 12:10, s. 1533-1540
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Tidskriftsartikel (refereegranskat)abstract
- At what point during translation do proteins fold? It is well established that proteins can fold cotranslationally outside the ribosome exit tunnel, whereas studies of folding inside the exit tunnel have so far detected only the formation of helical secondary structure and collapsed or partially structured folding intermediates. Here, using a combination of co-translational nascent chain force measurements, inter-subunit fluorescence resonance energy transfer studies on single translating ribosomes, molecular dynamics simulations, and cryoelectron microscopy, we show that a small zinc-finger domain protein can fold deep inside the vestibule of the ribosome exit tunnel. Thus, for small protein domains, the ribosome itself can provide the kind of sheltered folding environment that chaperones provide for larger proteins.
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| 7. |
- Armenteros, Jose Juan Almagro, et al.
(författare)
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Detecting sequence signals in targeting peptides using deep learning
- 2019
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Ingår i: Life Science Alliance. - : LIFE SCIENCE ALLIANCE LLC. - 2575-1077. ; 2:5
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Tidskriftsartikel (refereegranskat)abstract
- In bioinformatics, machine learning methods have been used to predict features embedded in the sequences. In contrast to what is generally assumed, machine learning approaches can also provide new insights into the underlying biology. Here, we demonstrate this by presenting TargetP 2.0, a novel state-of-the-art method to identify N-terminal sorting signals, which direct proteins to the secretory pathway, mitochondria, and chloroplasts or other plastids. By examining the strongest signals from the attention layer in the network, we find that the second residue in the protein, that is, the one following the initial methionine, has a strong influence on the classification. We observe that two-thirds of chloroplast and thylakoid transit peptides have an alanine in position 2, compared with 20% in other plant proteins. We also note that in fungi and single-celled eukaryotes, less than 30% of the targeting peptides have an amino acid that allows the removal of the N-terminal methionine compared with 60% for the proteins without targeting peptide. The importance of this feature for predictions has not been highlighted before.
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| 8. |
- Enquist, Karl, et al.
(författare)
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Membrane-integration characteristics of two ABC transporters, CFTR and P-glycoprotein
- 2009
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Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 387:5, s. 1153-1164
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Tidskriftsartikel (refereegranskat)abstract
- To what extent do corresponding transmembrane helices in related integral membrane proteins have different membrane-insertion characteristics? Here, we compare, side-by-side, the membrane insertion characteristics of the 12 transmembrane helices in the adenosine triphosphate-binding cassette (ABC) transporters, P-glycoprotein (P-gp) and the cystic fibrosis transmembrane conductance regulator (CFTR). Our results show that 10 of the 12 CFTR transmembrane segments can insert independently into the ER membrane. In contrast, only three of the P-gp transmembrane segments are independently stable in the membrane, while the majority depend on the presence of neighboring loops and/or transmembrane segments for efficient insertion. Membrane-insertion characteristics can thus vary widely between related proteins.
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| 9. |
- Fagerberg, Linn, et al.
(författare)
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Prediction of the human membrane proteome
- 2010
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Ingår i: Proteomics. - : Wiley. - 1615-9853 .- 1615-9861. ; 10:6, s. 1141-1149
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Tidskriftsartikel (refereegranskat)abstract
- Membrane proteins are key molecules in the cell, and are important targets for pharmaceutical drugs. Few three-dimensional structures of membrane proteins have been obtained, which makes computational prediction of membrane proteins crucial for studies of these key molecules. Here, seven membrane protein topology prediction methods based on different underlying algorithms, such as hidden Markov models, neural networks and support vector machines, have been used for analysis of the protein sequences from the 21 416 annotated genes in the human genome. The number of genes coding for a protein with predicted cc-helical transmembrane region(s) ranged from 5508 to 7651, depending on the method used. Based on a majority decision method, we estimate 5539 human genes to code for membrane proteins, corresponding to approximately 26% of the human protein-coding genes. The largest fraction of these proteins has only one predicted transmembrane region, but there are also many proteins with seven predicted transmembrane regions, including the G-protein coupled receptors. A visualization tool displaying the topologies suggested by the eight prediction methods, for all predicted membrane proteins, is available on the public Human Protein Atlas portal (www.proteinatlas.org).
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| 10. |
- Österberg, Marie, et al.
(författare)
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Phenotypic effects of membrane protein overexpression in Saccharomyces cerevisiae.
- 2006
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 103:30, s. 11148-11153
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale protein overexpression phenotype screens provide an important complement to the more common gene knockout screens. Here, we have targeted the so far poorly understood Saccharomyces cerevisiae membrane proteome and report growth phenotypes for a strain collection overexpressing ≈600 C-terminally tagged integral membrane proteins grown both under normal and three different stress conditions. Although overexpression of most membrane proteins reduce the growth rate in synthetic defined medium, we identify a large number of proteins that, when overexpressed, confer specific resistance to various stress conditions. Our data suggest that regulation of glycosylphosphatidylinositol anchor biosynthesis and the Na+/K+ homeostasis system constitute major downstream targets of the yeast PKA/RAS pathway and point to a possible connection between the early secretory pathway and the cells’ response to oxidative stress. We also have quantified the expression levels for >550 membrane proteins, facilitating the choice of well expressing proteins for future functional and structural studies.
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