TVI « Theoretical Biological Physics » (Prof. Erwin Frey) Louis Reese Betreuung durch Claus Heußinger Fluctuation-Driven Transmembrane Transport

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Outline 1.The Cell Membrane Protein activity in the Plasma Membrane Transport Through Membranes 2.Transport due to Fluctuations Modelling a Channel Protein Developing a Theoretical Model Solutions of the Fokker-Planck Equation 3.Outlook

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese The Cell Membrane Lipid bilayer hydrophilic hydrophobic Membrane maintains concentrations of solutes  Storage of Potential Energy Hydrophobic Molecules (O 2, CO 2 ) Small molecules, polar, uncharged (H 2 O, glycerol) Large molecules, polar, uncharged (glucose) Ions (H+, Na+, K+, …) MotivationHydrophobic barrier

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese The Plasma Membrane Plasma Membrane Ion gradients provide energy for ATP Synthese Transport mechanisms Electrical signals Cell Boundary Cytosol Membraneous Cell Compartments We need machines to perform these tasks: Membrane Proteins Ingest nutrients Excrete metabolic waste MotivationMembrane Activity

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Membrane Proteins ~30% of Genes (animals) encode Membrane Proteins Membrane Proteins ~50% of the membrane mass Membrane associated Reactions Connection to Cytoskeleton Transporter Sensors/Receptors (external Signals) MotivationProtein Functions Nonequilibrium Fluctuations Are supposed to be responsible for A. E. Pelling, et al. (2004)

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Functional Proteins asure selectivity Transport Through the Membrane MotivationTransmembrane Transport Active Pumping « Uphill » Coupled to catalysing energy-source (Light, ATP, coupled-Carriers) We’ll see soon that there are posibillities to make these Channels « WORK » Passive Facilitated Diffusion « Downhill » the Concentration gradient

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Transport due to Fluctuations The Glycerol uptake Facilitator (GlpF) Theoretical ModelMolecular Restraints   Na+Sugar Molecule X-Ray Structure shows Selectivity Asymmetric Potential of Mean Force (PMF) Finally a realistic Potential! Molecular Dynamics: M. Ø. Jensen, et al. (2002) Pulling Needed, but poisons the cell at high concentrations.

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Modelling Transport Brownian Motion: The Langevin Equation Theoretical ModelEquation of Motion  Virtual Friction  Virtual Realistic Potential of Mean Force  Langevin- Force: White Noise Membrane Fluctuation- Force

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Modelling the Transport Protein Probability densities Fokker-Planck Equation Theoretical ModelTransport FPE

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Details of Molecular Flux Theoretical ModelTransport Flux Composition of Flux through Channel DiffusionActing Forces Asymmetric Protein Potential + Membrane Fluctuation We know already: Zero-Force & Constant-Force

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Transport enhenced by external Force ResultsOutward Flux Periodic Force Periodic Force Despite Force: High Barrier  out  in  out Asymmetric Potential  Outward Transport

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Transport driven by Random-Telegraph-Force Fluctuating Force ResultsOutward Flux Random Force Poisson Mean Switching Time We still expect outward flux being better than inward flux. But 2 more Questions arise: 1.How do switching times influence transport? 2.Which role plays the concentration gradient?

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Switching Times tune Transport Switching very fast ~10 -9 s does not influence flux. Switching slowly ~10 -2 s, the time-dependence vanishes ResultsSwitching Time Tunes Transport ? In between, at equal concentrations:

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Concentration Gradient Regulates outward Transport Current reversal depends on concentration gradient. ResultsConcentration Gradient Regulates outward Transport  The passive Protein finally « WORKS » !

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Outlook Biological: Membrane Fluctuations could play a role in Cellular Transport Mechanisms –Protection against poisoning –Enhence nutrient uptake Theoretical Physics: Insight into processes spanning a timescale –From bottom-up simulations (~10 -9 s) to –Fluctuations (µs) to –Genetic mechanisms (~minutes) OutlookBiology Physics

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Take-Home Message Membranes –Make the difference between Life and Environment. Proteins –Are active or passive transporters –Molecular structure/symmetries are crucial! Membrane Fluctuations –Influence protein-transport properties! –Could be a hidden energy source

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Thank you for your attention!

Protein Fluorescence Fluctuation-Driven Transmembrane TransportLouis Reese Bibliography Results: I.Kosztin, K. Schulten, PRL 93, , 2004 Additional Material: B. Alberts et al., Molecular Biology of the Cell, (2002) 4th ed. M. Ø. Jensen, et al., PNAS 99, 6731 (2002) Homepage of Klaus Schulten. Previous Seminar Talks: „Forced thermal Ratchets“ „Fluctuation Driven Ratchets: Molecular Motors“ Appendix