SEC MALLs and AUC. 2. Conformation and flexibility Viscometry,

Transcription

1 1. Molecular weight distribution analysis SEC MALLs and AUC 2. Conformation and flexibility Viscometry, AUC, Light scattering

2 Lecture 5 Analytical Ultracentrifugation II: interactions Steve Harding

3 Free solution, no immobilisation, columns, membranes etc. needed. Self-association and hetero-interactions, stoichiometry, reversibility and strength (K eq, K d or ΔG o ) Use of sedimentation equilibrium and sedimentation velocity Self association or A-A A interactions, heterologous or A-B interactions How thermodynamic non-ideality yproblems are now dealt with experimentally & computationally (COVOL) Polysaccharide interactions, complex formation and mucoadhesion

4 Self-association: A+A A AA Association constant K eq = [AA]/[A] 2 -ml/mol, μm -1, M -1 Dissociation constant K d = [A] 2 /[AA] - mol/ml, μm, M Heterologous association: A + B AB Association constant K eq = [AB]/[A][B] - ml/mol, μm -1, M -1 Dissociation i constant t K d = [A][B]/[AB] -mol/ml, l μm, M M ΔG o = RTln K eq -J/mol K eq also given the symbol K 2 or K a

5 Interaction strengths commonly represented by K d values Strong interactions: K d < 1μM Medium interactions: 1μM < K d < 20μM Weak interactions: ti K d >20 20μM Very weak interactions: K d > 100μM NB this applies to reversible interactions

6 Sedimentation Velocity Sedimentation Equilibrium Centrifugal force Top view, sector of centrifuge cell Air Solvent Centrifugal force Diffusion Solution conc, c Rate of movement of boundary sed. coeff distance, r s o 20,w 1S=10-13 sec Shape, molecular weight & associated mass-action parameters, K d etc. conc, c distance, r STEADY STATE PATTERN FUNCTION ONLY OF MOL. WEIGHT PARAMETERS Molecular weight & associated massaction parameters, K d etc.

7 Thermodynamic non-ideality Radial distance Sedimentation c(r) () = f(m, B, Velocity K, r) Sedimentation Equilibrium (buoyant) Association or Centrifugal molecular force dissociation weight constant(s) Top view, sector of centrifuge cell Air Solvent Centrifugal force Diffusion conc, c Solution Rate of movement of boundary sed. coeff distance, r s o 20,w 1S=10-13 sec conc, c distance, r STEADY STATE PATTERN FUNCTION ONLY OF MOL. WEIGHT PARAMETERS Molecular weight & associated massaction parameters, K d etc.

8 Carbohydrate induced dimerisation of a protein M ~ 17.4kDa, K d ~ (120)μM MSTAR analysis M~30000 M~17400 cellulohexaose CBM29-2/E78R

9 Sedimentation equilibrium - Electron Transfer Flavoproteinheterodimer, M ~ 63kDa, K d ~ ( )μM European Biophys. J. (1997) 1. M wapp w,app analysis vs loading conc - stoichiometry. 2.M w,app (r) analysis - reversibility 3. Fitting the concentration distribution K d

10 Sedimentation equilibrium - Electron Transfer Flavoproteinheterodimer, M ~ 63kDa, K d ~ ( )μM 1. M wapp w,app analysis vs loading conc - stoichiometry. Blue chain: 29kDa; Purple chain: 34kDa 2.M w,app (r) analysis - reversibility 3. Fitting the concentration distribution K d

11 Thermodynamic non-ideality Radial distance Sedimentation c(r) () = f(m, B, Velocity K, r) Sedimentation Equilibrium (bouyant) Association or Centrifugal molecular force dissociation weight constant(s) Top view, sector of centrifuge cell Air Solvent Centrifugal force Diffusion conc, c Solution Rate of movement of boundary sed. coeff distance, r s o 20,w 1S=10-13 sec conc, c distance, r STEADY STATE PATTERN FUNCTION ONLY OF MOL. WEIGHT PARAMETERS Molecular weight & associated massaction parameters, K d etc.

12 B = f(excluded volume, charge) Ignoring B leads to incorrect K d Choice: 1.Ignore (valid only for strong interactions) 2.Calculate it on the basis of excluded volume theory

13 B = f(excluded volume, charge) Ignoring B leads to incorrect K d Choice: 1.Ignore (valid only for strong interactions) 2.Calculate it on the basis of excluded volume theory

14 B = f(excluded volume, charge) Ignoring B leads to incorrect K d Choice: 1.Ignore (valid only for strong interactions) 2.Calculate it on the basis of excluded volume theory theory quite complicated! but built into a simple to use program called COVOL

15 B = f(excluded volume, charge) Ignoring B leads to incorrect K d Choice: 1.Ignore (valid only for strong interactions) 2.Calculate it on the basis of excluded volume theory theory quite complicated! but built into a simple to use program called COVOL COVOL calculates B from size, shape and charge

16 CD2-CD48 cell recognition heterodimer: a weak interaction 2BM (from COVOL programme) = 10.4 ml/g K d = μm K d (from SPR) = μm (Anton van der Merwe) European Biophys. J. (1997)

17 Sedimentation Velocity Sedimentation Equilibrium Centrifugal force Top view, sector of centrifuge cell Air Solvent Centrifugal force Diffusion Solution conc, c Rate of movement of boundary sed. coeff distance, r s o 20,w 1S=10-13 sec Shape, molecular weight & associated mass-action parameters, K d etc. conc, c distance, r STEADY STATE PATTERN FUNCTION ONLY OF MOL. WEIGHT PARAMETERS Molecular weight & associated massaction parameters, K d etc.

18 Glue Protein Direction of sedimentation 0.8mg/ml 40,000 rpm, Scan every 10 min s 20,w = 2.3 Svedbergs Radial position (cm) Biochemistry (1998)

19 Glue Protein + Mucin Glue protein: 0.4mg/ml Mucin: 0.1mg/ml (invisible) 2000 rpm, Scan every 10min s ~ 7,000S 20,w Biochemistry (1998)

20 frictional ratio Hydrodynamic non-ideality Sedimentation Velocity Sedimentation c(r,t) ( ) = f(f/f (ff o M, Equilibrium k s, K, r, t) Centrifugal force Top view, sector of centrifuge cell Air Solvent molecular weight Association or dissociation constant(s) Centrifugal force Diffusion Solution conc, c Rate of movement of boundary sed. coeff distance, r s o 20,w 1S=10-13 sec Shape, molecular weight & associated mass-action parameters, K d etc. conc, c distance, r STEADY STATE PATTERN FUNCTION ONLY OF MOL. WEIGHT PARAMETERS Molecular weight & associated massaction parameters, K d etc.

21 frictional ratio Hydrodynamic non-ideality Sedimentation Velocity Sedimentation c(r,t) ( ) = f(f/f (ff o M, Equilibrium k s, K, r, t) conc, c Centrifugal force Top view, sector of centrifuge cell Air Solvent Solution Rate of movement of boundary sed. coeff distance, r s o 20,w 1S=10-13 sec Shape, molecular weight & associated mass-action parameters, K d etc. molecular weight Association or dissociation constant(s) Centrifugal force Diffusion - numerical solutions to Lamm equation (1923) s-distribution: Freeze-thaw bioprocessed IgG 4 conc, c distance, r STEADY STATE PATTERN FUNCTION ONLY OF MOL. WEIGHT PARAMETERS -nb Molecular single peak weight does not & associated necessarily mean mass- single solute! (Gilbert & Jenkins 1958) action parameters, K d etc.

22 frictional ratio Hydrodynamic non-ideality Sedimentation Velocity Sedimentation c(r,t) ( ) = f(f/f (ff o M, Equilibrium k s, K, r, t) Centrifugal force Top view, sector of centrifuge cell Air Solvent molecular weight Association or dissociation constant(s) Centrifugal force Diffusion conc, c Solution Rate of movement of boundary sed. coeff distance, r s o 20,w 1S=10-13 sec Shape, molecular weight & associated mass-action parameters, K d etc. c(s) method of P. Schuck attempts to correct for diffusion broadening conc, c distance, r STEADY STATE PATTERN FUNCTION ONLY OF MOL. WEIGHT PARAMETERS Molecular weight & associated massaction parameters, K d etc.

23 Sedimentation Velocity conc, c Centrifugal force Top view, sector of centrifuge cell Air Solvent Solution Rate of movement of boundary sed. coeff distance, r s o 20,w 1S=10-13 sec Shape, molecular weight & associated mass-action parameters, K d etc. Sedimentation Equilibrium Choice of software: conc, c 1.SEDFIT (P. Schuck): analysis of c(r,t) in terms of stoichiometry, reversibility Centrifugal force Diffusion 2.SC-ISOTHERM (A. Rowe et al) analysis of weight average sed.coeff. vs conc. in terms of stoichiometry & K d STEADY STATE PATTERN 3.SEDANAL (W. Stafford): global distance, analysis r of several FUNCTION ONLY c(r,t) s in terms of K d, k off (& k on ) OF MOL. WEIGHT PARAMETERS Molecular weight & associated massaction parameters, K d etc.

24 Demonstration of a protein switch: homodimerisation to heterodimerisation: Absence of apobccp87: homodimerisation metabolism transcription repression Top: fit by SEDFIT analysis Top: fit by SEDFIT analysis Bottom: residuals

25 Demonstration of a protein switch: homodimerisation to heterodimerisation: Absence of apobccp87: homo- dimerisation dimer monomer metabolism transcription repression as concentration increases, proportion of dimers increases

26 Demonstration of a protein switch: homodimerisation to heterodimerisation: Absence of apobccp87: homo-dimerisation metabolism transcription repression SC-Isotherm analysis: K d ~ (10+1) μm M

27 Demonstration of a protein switch: homodimerisation to heterodimerisation: Absence of apobccp87: homo-dimerisation metabolism transcription repression SC-Isotherm analysis: K d ~ (10+1) μm M SEDANAL analysis: k off = ( )x10-4 s -1 anything faster than 0.01 per second is considered as instantaneous. Too slow anything slower than per second won t distort the boundary enough

28 Demonstration of a protein switch: homodimerisation to heterodimerisation: Addition of apobccp87: switch from homo to hetero-dimerisation +0μM +5μM metabolism transcription repression +20μM K d (hetero-dimerisation) ~( ) μm

29 SC-ISOTHERM analysis CD2:CD48

30 Conformation analysis in associating systems e.g. take the case of a dimerising globular protein system or?

31 Neurophysin dimerises side by side - triaxial contour mapping (ELLIPS3) Λ Λ b/c R b/c monomer dimer (a/b)= 4, (b/c)= 1 (a/b)=2.5, (b/c)= 3 R a/b a/b a>b>c: triaxial semi-axes (sphere a=b=c) R: hydration independent function from viscosity & sedimentation Λ: viscosity & fluorescence depolarisation

32 Neurophysin dimerises side by side - triaxial contour mapping (ELLIPS3) Λ Λ b/c R b/c monomer dimer (a/b)= 4, (b/c)= 1 (a/b)=2.5, (b/c)= 3 R a/b a/b a>b>c: triaxial semi-axes (sphere a=b=c) R: hydration independent function from viscosity & sedimentation Λ: viscosity & fluorescence depolaristion & viscosity

33 and is bioprocessing-induced aggregation in antibodies linked to a conformation change in the monomer? Freeze-thaw bioprocessed IgG 4 Monomer, s=7.0s Requires measurement of properties of the monomer in the presence of aggregates: s, [η] (see Lecture 1) and other properties, modelled d using SOLPRO (see Lecture 4) an active area for current research!

34 Polysaccharide interactions Mucoadhesive interactions - chitosan Weak dimerisation arabinoxylan Self association of amino-celluloses

35 Mucoadhesive interactions - chitosan 1. Image by atomic force microscopy 2. Sedimentation velocity result Sedimentation coefficient s o 20,w ~ 1S Deacon et al, Biochem. J. 2000

36 Chitosan mucin complex 1. Image by atomic force microscopy 2. Sedimentation velocity result Sedimentation coefficient s o 20,w ~ 2000S Deacon et al, Biochem. J. 2000

37 Chitosan mucin complex 1. Image by atomic force microscopy 2. Sedimentation velocity result Sedimentation coefficient s o 20,w ~ 2000S very strong, irreversible interaction Deacon et al, Biochem. J. 2000

38 A very weak carbohydrate interaction: arabinoxylan dimerisation Expected behaviour for a non-interacting system very weak, reversible interaction Patel et al, Biophys. J. 2007

39 A very weak carbohydrate interaction: arabinoxylan dimerisation But it gives a +ve slope Expected behaviour for a non-interacting system very weak, reversible interaction Patel et al, Biophys. J. 2007

40 A very weak carbohydrate interaction: arabinoxylan dimerisation very weak, reversible interaction Patel et al, Biophys. J. 2007

41 Protein-like self-association in amino-celluloses! all M 1 ~ 20kDa 1.7S 2.3S 3.4S 43S 4.3S 5.5S Seems to associate into dimers, trimers, tetramers and pentamers, and with b ~0.7, more like a protein than a polysaccharide ( ) s ~ M b Daus et al, (mss in preparation)

42 Summary free solution technique for K d 's from <1μM to >100μM, and irreversible aggregation (e.g. antibodies) and complex formation phenomena (e.g. mucoadhesive complexes) major advances in both sedimentation velocity and equilibrium for stoichiometry, reversibility and strengths, self and hetero-associations and conformation analysis for reversible associations, complications through non- ideality, often need to be considered COVOL, for prediction of B.

43 Follow up bibliography: 1. Serydyuk, I.N., Zaccai, N.R. and Zaccai, J. (2006) Methods in Molecular Biophysics, Cambridge, Chapter D4 2. Harding, S.E., Rowe, A.J. and Horton, J.C., Eds (1992) Analytical Ultracentrifugation in Biochemistry and Polymer Science, Royal Soc. Chem. Cambridge 3. Scott, D.J. et al (2005) Analytical Ultracentrifugation. Techniques and Methods, Royal Soc. Chem. Cambridge 4. Brown, P.H., Balbo A. and Schuck, P. (2008) Characterizing protein- protein interactions ti by sedimentation ti velocity analytical l ultracentrifugation. Current Protocols in Immunology, 18, Harding S E Horton J C and Winzor D J (1998) COVOL: an 5. Harding, S.E., Horton, J.C. and Winzor, D.J. (1998) COVOL: an answer to your thermodynamic non-ideality problems?" Biochem. Soc. Trans