Biophysical studies of membrane proteins/peptides. Interaction with ...

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2.9. Lipid phase preferential partition of membrane proteins Many membrane proteins and peptides show a preference for bilayers in the fluid phase over the gel phase. This results in a difference in partition between domains when both phases coexist (Dumas et al., 1997). With even greater biological relevance, proteins exhibit also differential partition between liquid ordered and liquid disordered phases. In this way, the lateral structure of the lipid membrane is able to impose major restrictions to the lateral distribution of membrane proteins. Preferential partition of a membrane protein to a given region or phase of the membrane is likely to define important structural features, such as protein densities or the probability of protein encountering homologous or heterologous counterparts (see Section 2.11) (Pérez-Gil et al., 2005). Acylated proteins or lipid-anchored proteins will also preferentially partition to certain domains. Acylation with palmitic acid or myristic acid promotes preferential partition to more ordered domains such as membrane rafts. On the other hand, prenylated proteins are commonly excluded from liquid ordered domains (Epand, 2005). Changes of the lateral lipid membrane structure would thus have the ability to induce profound rearrangements of the protein lateral distribution. This would have major implications on the establishment of specific protein-protein interaction networks. In fact, it has been proposed that the natural membrane composition is optimized to maintain membranes on the threshold of a phase transition. Membranes in this situation would present a highly dynamical behaviour able to respond through redistribution of the protein network to environmental stimulus (Pérez-Gil et al., 2005). Hydrophobic matching might also be the mechanism by which proteins are targeted to their final destinations in the membrane. Sorting of proteins along the secretory pathway might be performed by means of a gradient of hydrophobic thickness of the membrane systems that the proteins have to pass on their way to their target. The concentrations of cholesterol and sphingomyelin, which have a thickening effect on the membrane, increase going from the endoplasmic reticulum, via the Golgi to the plasma membrane. Also, the hydrophobic domains of proteins that reside in the Golgi are shorter by about 5 amino acids when compared to those of the plasma membrane. 42
INTRODUCTION: LIPID-PROTEIN INTERACTIONS However, this proposed mechanism for sorting of membrane proteins is still controversial (Mouritsen, 2005). Concerning membrane protein partition to specific regions of the bilayer, of particular interest is the possibility that certain membrane proteins prefer insertion in the boundaries between lipid phases in the membranes. These boundaries present a higher probability of lipid packing defects that can be used by certain proteins to access deeper regions in the membrane (Pérez-Gil et al., 2005). 2.10. Lipid sorting by proteins and formation of lipid domains The presence of very stable lipid domains in the membrane is only expected if the free energies for interaction between phase separated lipids is very high. In biomembranes this is rarely the case, and therefore lateral structures that arise must have a reasonably dynamical nature. In model membranes, the differences in free-energies for lipid-lipid interactions are typically on the order of a few calories per mole. In contrast, the free-energies involved in protein-lipid interactions are much larger (Hinderliter et al., 2001). Therefore membrane proteins when incorporated in lipid membranes can contribute decisively to the final lipid phase equilibria. In the presence of a multicomponent lipid mixture in the fluid phase, insertion of a membrane protein can lead, as already described, to enrichment of one of the lipid species around the protein due to more efficient packing in the protein-lipid interface. This preferential association can stabilize a lipid phase around the protein, even under conditions where it is metastable in the protein-free system. This preferred phase is said to wet the protein (Gil et al., 1998). The wetting layer of lipids only extends over a finite (nonmacroscopic) distance. Theoretical studies have predicted that effects on lipids by inclusion of proteins may extend up to 20 lipid shells around the protein (Fattal and Ben-Shaul, 1993; Sperotto and Mouritsen, 1991), and results from some experimental studies were rationalized on the basis of wetting of membrane proteins and formation of lipid phases induced by protein-lipid interactions (Lehtonen and Kinnunen, 1997; Dumas et al., 1997; Hinderliter et al, 2004). 43
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UNIVERSIDADE TÉCNICA DE LISBOA INS
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Fernandes, F., Loura, L. M. S., Fed
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Ao Pedro e Hugo, amigos de longa da
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2.2. - Peptides as models 2.3. - Am
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ABBREVIATIONS AND SYMBOL LIST ABBRE
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RESUMO RESUMO As biomembranas são
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SINOPSE SINOPSE Nas últimas duas d
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Page 23 and 24: OUTLINE OUTLINE The last two decade
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Page 30 and 31: ion diffusion, as the energy requir
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Page 42 and 43: 1.7. Lateral heterogeneity in lipid
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Page 46 and 47: Figure I.9 - Depiction of the sever
Page 48 and 49: Figure I.11 - Experimentally obtain
Page 50 and 51: drying into a film and ressuspensio
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Page 68 and 69: Figure I.20 - Relative binding cons
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Page 75 and 76: PROTEIN-PROTEIN AND PROTEIN-LIPID I
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Page 83 and 84: 2430 Biophysical Journal Volume 85
Page 85 and 86: 2432 Fernandes et al. Coat protein
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Page 95: QUANTIFICATION OF PROTEIN-LIPID SEL
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Page 114 and 115: 5272 Biochemistry, Vol. 45, No. 16,
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5278 Biochemistry, Vol. 45, No. 16,
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BINDING ASSAYS OF INHIBITORS TOWARD
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1778 F. Fernandes et al. / Biochimi
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apparently the most significant as
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110
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Introduction Quinolones are broad-s
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[9-12]. Having this into considerat
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any case, very similar, probably wi
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placement of the protein around the
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⎛ II t ⎛ R ⎞ 0 ρ () t = exp
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APPENDIX - Derivation of the FRET r
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2 2w J ( t) = '2 R − R + w / 1
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[14] L. Plançon, M. Chami, L. Lete
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acceptors) (Eqs. 4-6) (⋅-⋅-⋅)
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FIGURE 1A FIGURE 1B 130
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136
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dynamin. Soon after, the same group
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140
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142
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Introduction Control of membrane re
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Steady-state fluorescence measureme
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Rho-DOPE (acceptor). The increase o
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where η is the viscosity of the me
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ound conformation of the BAR domain
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19. Fernandes, F., L. M. S. Loura,
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Figure Legends Fig.1: N-terminal am
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FIG. 1A FIG.1B 17
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FIG. 3A FIG. 3B 19
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FIG.5A 21
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FIG 6. 23
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FIG. 8 A B 25
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The signalling functions of PI(4,5)
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172
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174
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zoxadiazol (NBD)-PC were obtained f
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Fig. 3. Fluorescence decays of diph
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CONCLUSIONS VII CONCLUSIONS Chapter
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CONCLUSIONS constants recovered by
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CONCLUSIONS Chapter IV ‐ Binding
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CONCLUSIONS Chapter VI - Clustering
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FINAL CONSIDERATIONS AND PROSPECTS
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BIBLIOGRAPHY IX BIBLIOGRAPHY Albert
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BIBLIOGRAPHY Phosphatidylinositol 4
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BIBLIOGRAPHY Glaubitz, C., Grobner,
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BIBLIOGRAPHY Koehorst, R. B. M., Sp
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BIBLIOGRAPHY Mishra, V. K., Palguna
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BIBLIOGRAPHY Pluschke, G., Hirota,
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BIBLIOGRAPHY Sperotto, M. M., and M
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BIBLIOGRAPHY Williamson, I. M., Alv
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