Fajun Zhang, Roland Roth, Marcell Wolf, Felix Roosen-Runge, Maximilian W. A. Skoda, Robert M. J. Jacobs, Michael Stzuckie and Frank Schreiber

Transcription

1 Soft Matter, 2012, 8, 1313 Fajun Zhang, Roland Roth, Marcell Wolf, Felix Roosen-Runge, Maximilian W. A. Skoda, Robert M. J. Jacobs, Michael Stzuckie and Frank Schreiber Universität Tübingen, Institut für Angewandte Physik - 1st December 2011 Stijn Koshari Chemical and Biomolecular Engineering

2 OVERVIEW 2/35

3 OVERVIEW 3/35

4 OVERVIEW 4/35

5 0. Overview 1. Introduction 2. Approach 3. SAXS 4. Discussion 5. Crystallization 6. Conclusion CHARGE-CONTROLLED LLPS 5/35

6 Charge-controlled phase separation Metastable liquid-liquid phase separation (LLPS) CHARGE-CONTROLLED LLPS 6/35

7 Protein solutions stabilized by (DLVO): van der Waals forces Electrostatic forces (surface charges) Change of ion concentration in solution can affect surface charge Effective interactions Hence, may lead to aggregation Compare to colloids, but more complex INTRODUCTION 7/35

8 F. Zhang, et al. Phys. Rev. Lett., 2008, 101, INTRODUCTION 8/35

9 Two liquid phases: Protein-rich Condensation (gel) Protein-poor Crystallization Metastable INTRODUCTION 9/35

10 INTRODUCTION 10/35

11 Two liquid phases: Protein-rich Condensation (gel) Protein-poor Crystallization Metastable: Merge and grow Density fluctuations Important phenomenon: Universal, but not often observed Prerequisite for protein aggregation diseases Crystallization (controlled) INTRODUCTION 11/35

12 Materials Methods CHARGE-CONTROLLED LLPS 12/35

13 Protein: Human serum albumin (HSA) Globular medium sized (67 kda) Negatively charged Salt: Yttrium chloride YCl 3 Trivalent salt Cation binds to acidic residues (Asp, Glu) Charge inversion APPROACH 13/35

14 F. Zhang, et al. Phys. Rev. Lett., 2008, 101, APPROACH 14/35

15 Determine phase diagram for a fixed temperature Vary protein and salt concentration Observation techniques Optical microscopy X-ray and ultra-violet light absorption Small-angle X-ray spectroscopy (SAXS) APPROACH 15/35

16 APPROACH 16/35

17 Concept Dilute samples Concentrated samples LLPS criteria CHARGE-CONTROLLED LLPS 17/35

18 Small-angle X-ray spectroscopy X-ray EM wave interacts with orbital electrons Fluctuations in sample lead to structure Information about gross characteristics A. Sali, et al. ( (2013). SAXS 18/35

19 SAXS 19/35

20 Particle positions are uncorrelated Form factor gives general information about particle: Low : Guinier limit Radius of gyration High : Porod limit Fractal information Overall shape Particle shape SAXS 20/35

21 SAXS 21/35

22 Particle positions are correlated (rotation, position) Form factor gives general information about particle determine from dilute sample and remove Structure factor gives general information about particle interactions: Low Compressibility Overall shape Particle distribution/structure SAXS 22/35

23 SAXS 23/35

24 Structure factor fitting gives information about particle interactions: Assume sticky hard sphere (SHS), short ranged square well Fitted stickiness parameter is directly related to the second virial coefficient Second virial coefficient is a measure for strength of interactions Both and have critical values which indicate occurrence of LLPS SAXS 24/35

25 Results Origin of interactions CHARGE-CONTROLLED LLPS 25/35

26 DISCUSSION 26/35

27 DISCUSSION 27/35

28 Physical origin of short-range attraction remains to be identified: van der Waals Solvation Structural forces Protein-Y 3+ complexes can be highly complex: Non-spherical shape Nonhomogeneous surface charge pattern Complex hydration properties DISCUSSION 28/35

29 Crystal growth control Crystallization criterion CHARGE-CONTROLLED LLPS 29/35

30 Possibility for high quality protein single crystals Two-step or single-step procedure at same temperature Play with ion concentration Changing temperature can further help optimize crystallization conditions Already used CRYSTALLIZATION 30/35

31 CRYSTALLIZATION 31/35

32 Second virial coefficient good predictor of protein crystallization Shown to have almost constant value at critical point Thermodynamic criterion CRYSTALLIZATION 32/35

33 CHARGE-CONTROLLED LLPS 33/35

34 Use trivalent ions to control phase behavior of proteins Consistent and comprehensive understanding Experimental and thermodynamic evidence Universal applicability CONCLUSION 34/35

35 Thank you for your applause