| 1. |
- Boekel, Carolina, 1977-
(författare)
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Integration and topology of membrane proteins
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Membrane proteins comprise around 20-30% of most proteomes. They play important roles in most biochemical pathways. All receptors and ion channels are membrane proteins, which make them attractive targets for drug design. Membrane proteins insert and fold co-translationally into the endoplasmic reticular membrane of eukaryotic cells. The protein-conducting channel that inserts the protein into the membrane is called Sec61 translocon, which is a hetero-oligomeric channel that allows transmembrane segments to insert laterally into the lipid bilayer. The focus of this thesis is how the translocon recognizes the transmembrane helices and integrates them into the membrane.We have investigated the sequence requirements for the translocon-mediated integration of a transmembrane α-helix into the ER by challenging the Sec61 translocon with designed polypeptide segments in an in vitro expression system that allows a quantitative assessment of membrane insertion efficiency. Our studies suggest that helices might interact with each other already during the membrane-insertion step, possibly forming helical hairpins that partition into the membrane as a single unit. Further, the insertion efficiency for Nin-Cout vs. Nout-Cin transmembrane helices and the integration efficiency of Alzheimer’s Aβ-peptide fragments has been investigated.Finally, detailed topology mapping was performed on two biologically interesting proteins with unknown topology, the human seipin protein and Drosophila melanogaster odorant receptor OR83b.
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| 2. |
- Lara Vasquez, Patricia, 1982-
(författare)
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Integration and topology of membrane proteins related to diseases
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Membranes are boundaries that separate the cell from the external environment. Membrane proteins can function as e.g. receptors and channels, allowing cells to communicate with the exterior and molecules to pass through the membrane. The biogenesis of membrane proteins involves a protein-conducting channel that aids the hydrophobic segments to partition into the membrane and translocate the hydrophilic loops. Membrane proteins need to fold to its native conformation including post-translational modifications and assembly with other proteins and/or cofactors. If this regulated pathway goes wrong the degradation machinery degrades the protein. If the system is failing can result in serious disorders. The main focus in this thesis is membrane proteins associated to diseases.We have studied mutations in the gene of presenilin 1, which is involved in Alzheimer’s disease. We found that some mutations affect the structure and other the function of the PS1. URG7 is an unknown protein associated with liver cancer. We suggest it is localized and targeted to the ER membrane, having an NoutCin topology. SP-C is important for our lungs to function. Mutations can cause the protein to aggregate. We have studied the highly Val-rich transmembrane segment (poly-Val) and its analogue (poly-Leu) and show that poly-Leu folds into a more compact conformation than poly-Val. We show that the C-terminal chaperon-like BRICHOS domain interacts with the ER membrane, suggesting an involvement in poly-Val folding. We have also confirmed the topology of URG7, MRP6 and SP-C poly-Val/Leu using gGFP that is fused to the C-terminal of the protein.
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| 3. |
- Nilsson, IngMarie
(författare)
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Conformational properties of transmembrane polypeptide segments in the ER membrane
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We have developed a new experimental approach where the active site of oligosaccharyl transferase is used as a point of reference against which the position of a transmembrane segment in the membrane can be measured. This so-called glycosylation mapping technique allows any transmembrane segment to be positioned relative to a known reference transmembrane helix with known position in the membrane. We have studied the position of transmembrane polypeptides in the ER membrane and determined the effects of single proline and charged residues on the position of a transmembrane helix in the endoplasmic reticulum membrane using the glycosylation mapping technique. We have found that proline residues can break a transmembrane helix when inserted near the end of the helix, but not when placed more centrally and only when the helix is sufficiently long. Compared to the helix-disrupting effects seen with proline residues, the charged amino acid residues cause less drastic changes. We suggest that charged residues do not break the helical conformation but just affect the position of the helix in the membrane. The difference between the effects of positively and negatively charged residues can be explained by the so-called snorkel effect, i.e. that the very long side-chains of Arg and Lys can reach up along the transmembrane helix to allow the terminal charged moiety to reside in the lipid head group region. Our results from a turn propensity investigation suggest that in a very long transmembrane helix, twice as long as a normal helix, a single proline residue introduced near the center of the helix can induce the formation of two transmembrane segments separated by a tight turn. The glycosylation mapping technique may be generally useful for determining the position of transmembrane helices in the membrane and the ends of different transmembrane segments.
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| 4. |
- Stridfeldt, Monika
(författare)
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La perception du français oral par des apprenants suédois
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Swedish learners of French often experience large difficulties in understanding spoken French. Words that the learners know very well when written or when pronounced separately are often hard to recognize in the speech flow. The aim of this study is to examine Swedish learners’ perception of French speech in order to identify the problems.The thesis consists of two parts. The first part provides an introduction to the perception of a second language. It also describes the phonological structures of Swedish and French and gives an overview of studies of the perception of spoken French.The second part of the thesis contains a presentation and an analysis of four perception experiments conducted with Swedish learners of French. The results show that the learners often confuse phonological contrasts that do not exist in Swedish. It is furthermore found that the phonological processes of schwa deletion, liaison, enchaînement and voicing assimilation contribute to the perception problems. However, although liaison may complicate word recognition the results indicate that the so-called potential liaison does so to an even greater extent. In a listening test using nonsense words, the learners seem actually to expect liaison when perceiving a word that can be linked to a following nonsense word. In fact, sequences like un navas and un avas are both perceived as un avas. Paradoxically, liaison thus seems to be most problematic when it does not occur.As to schwa deletion, the results show that word recognition is delayed when the schwa in the first syllable is deleted, as in la s’maine. In addition, the learners make a large number of errors due to schwa deletion. This phonological process sometimes completely prevents word recognition, especially when combined with a voicing assimilation. Schwa deletion thus seems to strongly complicate Swedish learners’ word recognition in spoken French.
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