Membrane Bioinformatics SoSe 2009 Helms/Böckmann

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Membrane Bioinformatics SoSe 2009 Helms/Böckmann. Membrane-protein-interaction. Protein function. Drug transport in liposomes. Thermodynamics of Membranes. Why important?. O. Mouritsen Life – as a Matter of Fat Springer (2005). Thermodynamics of Membranes. - PowerPoint PPT Presentation

Transcript of Membrane Bioinformatics SoSe 2009 Helms/Böckmann

  • *Membrane Bioinformatics SoSe 2009Helms/Bckmann

  • *Thermodynamics of MembranesWhy important?O. Mouritsen Life as a Matter of Fat Springer (2005)

  • *Thermodynamics of MembranesLipid membranes have the ability to adopt different phases.Measurement: Microcalorimetry-measurement of the excess heat to increase the temperature of the material from T to T+TLipowski & Sackmann Structure and Dynamics of Membranes Elsevier (1995)

  • *Thermodynamics of MembranesTh. Mehnert PhD Thesis TU Mnchen (2004)

  • *Thermodynamics of MembranesTemperature dependent phases:L: fluid phase

    P: ripple phase, solid & fluid (periodic structure)

    L: crystalline, chains tilted

    Lc: crystallineS. Pisch-Heberle PhD Thesis Uni Stuttgart (2000)

  • *Thermodynamics of MembranesAll-trans / gauge isomerisation:Th. Heimburg NBI CopenhagenDifferent conformations of lipid chains by rotation around the C-C bonds (trans-gauche isomerisation):Lowest energy: all-trans conformation (zigzag)Gauche-isomer: larger enthalpic energy but also larger entropy!Lipid conformation is temperature dependent!

  • *Thermodynamics of MembranesRipple phase P observed for a DPPC bilayer in experiments:D.Czajkowsky et al. Biochemistry 34 (1995) 12501-12505Two different domains with different thickness (X-ray)High degree of tail stretching (FTI, NMR)Organisation of lipids unknown

  • *Thermodynamics of MembranesRipple phase P observed for a DPPC bilayer in experiments:O. Mouritsen Life as a Matter of Fat Springer (2005)AFM picture ripple phase of a DPPC bilayer in water(600nm x 600nm)

  • *A.H. de Vries et al. PNAS 102 (2005) 5392-5396Thermodynamics of MembranesRipple phase P observed for a DPPC bilayer in molecular dynamics simulations:

  • *A.H. de Vries et al. PNAS 102 (2005) 5392-5396Thermodynamics of MembranesRipple phase P observed for a DPPC bilayer in molecular dynamics simulations:Ripple phase consists of two domains of different length and orientation, connected by a kink

    First domain: like splayed gel

    Second domain: fully interdigitated, gel-like lipids

    Lipids disordered in the concave part of the kinks

  • *Thermodynamics of MembranesTransition temperature increases with increasing chain length

    Tm(PE) > Tm(PC)

    transition temperature increases with increasing packing density: area(PE)

  • *Thermodynamics of MembranesTransition temperature increases with increasing chain length:

    Transition temperatureFor Dialkyl-Phosphatidylethanolamine:Free enthalpy at transition (t) point:PE/PC lipids show similar increments for Ht and St:P L mainly determined by cohesion of the hydrocarbon chains! Lipowski & Sackmann Structure and Dynamics of Membranes Elsevier (1995)

  • *Thermodynamics of MembranesTransition temperatureVariation of chain melting temperatures of 18:1 lipid bilayers with position of double bond within the chain:Influence of Carbon Saturation on Phase Transition:Largest decrease in melting temperature observed for double bond in the center of the chainsLipowski & Sackmann Structure and Dynamics of Membranes Elsevier (1995)

  • *Thermodynamics of Membranesoccur at defined temperatures

    Depend on:

    Chain lengthDegree of saturationLipid chargeHeadgroup size (transition temperature increases with increasing packing density)Phase transitions:Transition temperatures depend on:Cholesterol contentPresence of proteinsPresence of anesthetics (chloroform, alcohol, ..)

  • *Thermodynamics of MembranesSome general considerations(1) Probability of state i with energy Ei:(2) Entropy: sum over all states i (also degenerated states)(3) Partition function:

  • *Thermodynamics of MembranesSome general considerations(4) Density of states (E):Energy distribution:canonical partition funcionAverage energy:Large number of particles N:

  • *Thermodynamics of MembranesSome general considerationsDuhem-Gibbs relation:Thus the entropy is proportional to ln(density of states)!Re-write the partition function:sum over states with different energies

  • *Thermodynamics of MembranesLipid states:Simplified lipid carbon chain: rotation by 120o: change from trans to gauche conformationProbability of excited state 1 (gauche) and ground state 0 (trans):With

  • *Thermodynamics of MembranesGround state = all-trans (all angles =0):General case (probability of finding CH2CH2 bond in excited gauche state)Equal distribution between all states at high temperature (T): Entropy of unordered state proportional to the chain length n (two chains per phospholipid):Enthalpy of unordered/excited state:

  • *Thermodynamics of MembranesTypical values: phosphatidylcholines (2 chains):Assumption: only two possible states, all-trans and all-gaucheThe melting temperature is then given by:The transition temperature of lipids is in the physiological range of -20oC to +60oK!

  • *Thermodynamics of MembranesCooperativity:The equilibrium constant K is temperature dependent:: vant Hoff lawAverage enthalpy change/mol:probability of excited stateHeat capacity:

  • *Thermodynamics of MembranesCooperativity:Heat capacity:With : width of transition curve cp(T) approx. 60oC!But: Experiment: width of transition curve cp(T)