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Induced lipid chirality near a protein inclusion /

by Raciti, Domenica (Mimma) [aut]; Ferrarini, A [ths]; Raudino, Antonio [ths].
Material type: materialTypeLabelBookPublisher: Catania : Scuola Superiore di Catania, 2017Description: [iii], 66 p. : ill. ; 25 cm.Subject(s): Proteins -- Structure
Contents:
Abstract -- Introduction -- Conceptual grounds -- Modelling approach -- Overview on membrane energetics -- Theoretical model -- Results -- Possible improvements -- Conclusions -- Appendix : Comment on the elastic moduli -- Mass conservation constraint -- Solution of the constitutive equations -- Comments on lipid chirality -- Acknowledgements -- References.
Dissertation note: Tesi di diploma di 2° livello per la Classe delle Scienze Sperimentali Diploma di 2° livello Scuola Superiore di Catania, Catania, Italy 2017 A.A. 2016/2017 Abstract: Chiral solutes, like proteins, may alter the properties of nearby molecules, so that the latter may take a chiral arrangement. This induced chirality, resulting from the anisotropy of (chiral) solute-solvent interactions, may add new functionality to the system. Motivated by the biological relevance of chirality in membrane function, this thesis tackles the poorly studied problem of protein-induced lipid chirality. An analytic model was developed, based on the liquid crystal continuum theory to predict the lipid behaviour around a cylindrical, chirally patterned inclusion (mimicking a membrane-spanning protein). The key parameters are the hydrophobic mismatch between protein and membrane thicknesses and the preferred direction (easy axis) of protein-lipid interactions. The membrane deformation profile was obtained by energy minimization and used to calculate the lipid torsion angle (a chirality descriptor). Chiral arrangements of lipids around the chiral inclusion were theoretically predicted and qualitatively confirmed by MARTINI Molecular Dynamics simulations of lipid-protein model systems ([alpha]-helix and [beta]-barrel). The enantiomeric excess, proportional to the lipid torsion angle was quantified. The effect is supposedly modest, unless precise conditions are fulfilled: negative hydrophobic mismatch, anisotropic protein-lipid interactions higher than kT, sufficiently large protein radii, rod-shaped lipids, low temperatures or locally ordered membrane phases. The length of chiral propagation depends on membrane composition, but seems to be limited to a few protein solvation shells (the annular lipids). Therefore, only some real systems are expected to exhibit biophysically relevant chirality induction, e.g. large proteins (barrels, bundles) and locally ordered lipid phases (rafts). The issue of induced lipid chirality deserves further investigation, with special regard to the interaction kinetics between chirally-dressed proteins (of same vs opposite chirality). Tailored experiments and extensive MD investigations will be needed to this aim. Hopefully, this could help understand the complex membrane functionality.
List(s) this item appears in: Tesi di Laurea, Diploma, Dottorato, Master
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Location Call number Status Date due
Sala B : Armadio Tesi THS_2017 572.6 R121 (Browse shelf) Available

Tesi di diploma di 2° livello per la Classe delle Scienze Sperimentali Diploma di 2° livello Scuola Superiore di Catania, Catania, Italy 2017 A.A. 2016/2017

Includes bibliographical references (p. 60-66).

Abstract -- Introduction -- Conceptual grounds -- Modelling approach -- Overview on membrane energetics -- Theoretical model -- Results -- Possible improvements -- Conclusions -- Appendix : Comment on the elastic moduli -- Mass conservation constraint -- Solution of the constitutive equations -- Comments on lipid chirality -- Acknowledgements -- References.

Tesi discussa il 11/12/2017.

Chiral solutes, like proteins, may alter the properties of nearby molecules, so that the latter may take a chiral arrangement. This induced chirality, resulting from the anisotropy of (chiral) solute-solvent interactions, may add new functionality to the system. Motivated by the biological relevance of chirality in membrane function, this thesis tackles the poorly studied problem of protein-induced lipid chirality. An analytic model was developed, based on the liquid crystal continuum theory to predict the lipid behaviour around a cylindrical, chirally patterned inclusion (mimicking a membrane-spanning protein). The key parameters are the hydrophobic mismatch between protein and membrane thicknesses and the preferred direction (easy axis) of protein-lipid interactions. The membrane deformation profile was obtained by energy minimization and used to calculate the lipid torsion angle (a chirality descriptor). Chiral arrangements of lipids around the chiral inclusion were theoretically predicted and qualitatively confirmed by MARTINI Molecular Dynamics simulations of lipid-protein model systems ([alpha]-helix and [beta]-barrel). The enantiomeric excess, proportional to the lipid torsion angle was quantified. The effect is supposedly modest, unless precise conditions are fulfilled: negative hydrophobic mismatch, anisotropic protein-lipid interactions higher than kT, sufficiently large protein radii, rod-shaped lipids, low temperatures or locally ordered membrane phases. The length of chiral propagation depends on membrane composition, but seems to be limited to a few protein solvation shells (the annular lipids). Therefore, only some real systems are expected to exhibit biophysically relevant chirality induction, e.g. large proteins (barrels, bundles) and locally ordered lipid phases (rafts). The issue of induced lipid chirality deserves further investigation, with special regard to the interaction kinetics between chirally-dressed proteins (of same vs opposite chirality). Tailored experiments and extensive MD investigations will be needed to this aim. Hopefully, this could help understand the complex membrane functionality.

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