solution scattering, an overvie · radiation interacts with atoms and/or their nuclei. for the...
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SolutionScattering,an Overview
Heinrich B. Stuhrmann
GKSS Forschungszentrum andInstitut de Biologie Structurale Jean-Pierre Ebel
CEA / CNRS, Grenoble, France
EMBO Practical Course on Solution Scattering fromBiological Macromolecules
EMBL, Hamburg, September 5-14, 2001
Organizers:D. Svergun, EMBL Outstation Hamburg
R. Willumeit, GKSS Research Centre, Geesthacht
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case: small-angle scattering from a monodisperse dilute solutionof macromolecules
solvent
solute
2θθθθ
scat
terin
g in
tens
ity
scattering angle
few degrees
A.Guinier: I(Q) = C exp(R2Q2/3)
Q = 4π/λ sinθ λ = wavelength
R = radius of gyration
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CHEMIE IN UNSERER ZEIT (1979)
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Contrast with macromolecules :
Radiation interacts with atoms and/or their nuclei.
For the present pourpose, the strength of intertaction isdescribed by the scattering length b.
In a volume containing a reasonably large number of atomsit is convenient to define the scattering length density (orscattering density) :
ρ = Σn bn / volume
For a macromolecule in solution:
Contrast : ρ ( r ) : = ρ ( r )MM - ρ solvent
-6000
-4000
-2000
0
2000
4000
6000
-6000 -4000 -2000 0 2000 4000 6000
a biological macromolecule in solution
example:catalase: x,z plane:
r
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Contrast variation
variation of solvent density(external contrast variation,or solvent contrast variation)
variation of the scattering density of parts ofa macromolecule(internal contrast variation)
From real spaceto momentum space
A(Q) = v ρ(r) exp(iQr) dv
|Q | = 4 π sin θ / λ, 2θ = scattering angle, λ = wavelength
A(Q) = U(Q) + x V(Q)
↑↑↑↑ contrast, in a wide sense
The expression for the intensity I(Q) may vary. In thesimplest case it is given by
I(Q) = |U(Q)|2+ x 2Re[U(Q)V*(Q)] + x2 |V(Q)|2
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For small-angle scattering from randomlyoriented particles I(Q) is the the result of anintegration over all orientations of thedissolved particles. The basic scatteringfunctions are obtained by variation of x.
Contrast variation startet with X-ray diffraction fom ahemoglobin crystal ( Bragg & Perutz, 1952).
Considerable changes of the low order reflections ofhemoglobin were observed with the varaition of the electrondensity of the solvent.
packing of the hemoglobin molecules in the unit cell
This method is the precursor of multiwavelength anomaloussolvent contrast variation (MASC) (Fourme et al. 1995)
x = f ' + i f ''
Hence
I(Q) = |U(Q)|2+ f ' 2Re[U(Q)V*(Q)] + f '' 2Im[U(Q)V*(Q)]
+ (f '2 + f ''2 ) |V(Q)|2
Note the presence of four basic scattering functions
shape and packing of the proteins in the unit cell.
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Anomalous small-angle scattering
I(Q) = |U(Q)|2+ f ' 2Re[U(Q)V*(Q)] +(f '2 + f ''2 ) |V(Q)|2 dΩ
Example: phosphorus of rRNA of the large ribosomalsubunit.
Anomalous dispersion at wavelengths near the K-edge ofphosphorus ( λλλλ = 5.76 Å ) (M. Hütsch, 1995)
Variation of anomalous scattering length with λ: 16 e.u.( 1 e.u. = scattering length of one electron = 0.28E-12 cm )Local concentration of P : up to 3 M / l
in situ structure of rRNA at low resolution
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In the mid sixties, solvent contrast variation was used in small-anglescattering. The electron density was varied by addition of glycerol orsugar. Variation of the radius of gyration with contrast inmyoglobin.
With the advent of high flux neutron sources, contrast variation isalmost entirely done byexchange of the hydrogen isotope 1H by 2H (Deuterium).
- High abundance: 70 H / nm3 (110 M/l)
- Large change of scattering length: 0.69E-12 cm (corresponds to the scattering length of 2.5 electrons in X-ray scattering).
Applications of solvent contrast variation were numerous :
Ribosomes, Chromatin, RNA polymerase,Viruses,Lipoproteins
The constituents of these particles are
H / nm3 scattering density matched by
RNA/DNA 40 high 70% D2O
Proteins 60 medium 40% D2O
Lipids 70 low water
low resolution architecture (quaternary structure)
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Examples of internal contrast variation:
Ribosomes:
The positions of all 21 proteins of the small ribosomal subunit were found bytriangulation between specific deuterated ribosomalproteins ( D.M. Engelman & P.B. Moore, W. Hoppe).
The method of triple isomorphous replacement uses fully and partiallydeuterated proteins as labels (I. Serdyuk).
It resembles in some respects a method which uses the
change of the scattering length of hydrogen with protonspin polarisation in polarised neutron small-anglescattering.
x = P ( = proton spin polarisation)
The intensity of polarised neutron small-angle scattering is
I↑↑(Q) = |U(Q)|2 + P 2Re[U(Q)V*(Q)] + P2 |V(Q)|2 dΩ
if the direction proton spins coincides with that of the neutron spins
I↓↑ (Q) = |U(Q)|2 – P 2Re[U(Q)V*(Q)] + P2 |V(Q)|2 dΩ
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The method of proton spin contrast variationwas used to detemine the in situ structure ofthe tRNAs and of the mRNA, i.e. the positionand orientation of these molecules inside thethe functional ribosome.
Largest variation of the scattering length withthe polarisation of the proton spins:
(− 0.56 ± 1.456 P) 10-12 cm
corresponding to 10 electron units in X-rayscattering
Best results are obtained with particles which have beendeuterated. Only the regions of interest are leftprotiated.For biological macromolecules a mixture of deuteratedglycerol and heavy water is a convenient solvent.
The deuterons are polarised as well, although to anextent which is much lower than that of the protons:Their scattering length changes as well:
(0.66 ±0.27 P(D)) 10-12 cm
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Uranium, MV edge
-1000
-500
0
500
1000
1500
35100 35200 35300 35400 35500 35600 3570energy [0.1 eV]
f
f'
f"
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Neutron scattering from hydrogen:
The neutron and the nucleus of 1H (=proton) have a spin ½.
There are two different channels of neutron-proton interaction:- one for the total spin ½ + ½ = 1 with b+ ( 3 substates)- one for the total spin ½ − ½ = 0 with b− ( 1 substate )
The effective length b of coherent scattering is the weighted averageof b+ and b− . With b+ = 1.083 10-12 cm and b− = − 4.74 10-12 cm we obtain
b = ¾ b+ + ¼ b− = −−−−0.374 10-12 cm for 1H
A similar calculation yields for 2H (=Deuterium)b = + 0.66 10-12 cm for D
This difference is the basis for practically all application of isotopicmethods of contrast variation in biology and soft condensed matterresearch in general.
Incoherent scattering :
σ(incoh.) = 3π/4 (b+ − b−)2 = 79.9 10-24 cm2 for 1H
σ(incoh.) = 2.0 10-24 cm2 for 2H
Incoherent scattering from 1H is reduced by deuteration
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Polarised neutron scattering frompolarised nuclear spins of hydrogen:
Both the neutron and the nucleus of 1H (=proton) have aspin ½.
There are two different channels of neutron-proton interaction:- one for the total spin ½ + ½ = 1 with b+ ( 3 substates)- one for the total spin ½ − ½ = 0 with b− ( 1 substate )
If the neutron spins are polarised in the same direction as theproton spins then the length b of coherent scattering isb(↑↑↑↑↑↑↑↑ ) = b+ = 1.083 10-12 cm
If the neutron spins are polarised antiparallel to the directionof the proton spins then the length b of coherent scattering isb(↑↑↑↑↓↓↓↓ ) = (b+ + b−−−−)/2 = −−−− 1.83 10-12 cmb(H) = [−0.374 ± 1.456 P(H) ] 10-12 cm
A similar calculation yields for 2H (=Deuterium)b(↑↑↑↑↑↑↑↑ ) = 0.93 10-12 cmb(↑↑↑↑↓↓↓↓ ) = 0.39 10-12 cmb(D) = [ 0.667 ± 0.27 P(D) ] 10-12 cm
Incoherent scattering :
σ(incoh.) = π (b+ − b−)2 ( ¾ ± ½P − ¼ P2)
Incoherent scattering from 1H is reduced by deuteration..and , even more easily, by polarisation of the proton spins indirection of neutron spin polarisation
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How to polarize proton spins
by 'brute force'
-2
-1,5
-1
-0,5
0
0,5
1
1,5
0,1 1 10 100 1000 10000 100000
B[T] / T[K]
scat
terin
g le
ngth
[1.0
E-1
2 cm
]
H
DN
e -
How to polarize proton spins
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by 'dynamical nuclear spin polarisation' (DNP)
In the presence of convenient paramagnetic centres,all nuclear spins are dynamically polarisedby irradiation of 2.8 mm microwavesin a field of 3.5 Tesla,at temperatures T <= 1 K.
The polarisation is monitored by NMR:
EPR of the tyrosyl radical
97.3 GHz(2.8 mm microwaves)
-150 MHz +150 MHz
negative nuclear spin polarisationpositive nuclear
spin polarisation
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The protons near the paramagnetic centreusually remain unobserved.
The direction of proton spin polarisation can be reversedby the method of adiabatic fast passage (AFP). If the rfscan is restricted to frequencies of the central peak, thenonly the protons of the bulk will change their polarisationdirection.
148 MHz
proton NMR of the tyrosyl radical at T=1K, in a magnetic field of 3.5 T
from protons in the bulk
from protons near the paramagnetic centre
20 kHz
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In dilute paramagnets, DNP is described by the'well resolved solid effect' :
Nuclear polarisation....- develops first near the paramagnetic centres- and then diffuses into the bulk.
At very low concentration of radicals (orparamagnetic centres in general) the effect of DNPcannot be observed by NMR.Is DNP is confined to the magnetically perturbedregion near the paramagnetic centre ?
Tyrosyl doped catalase is such an example.
C < 0.5 mM/l ( < 1.8E+17 e– /cm3)
Preparation:
A small amount of peroxy acetic acid is added to asolution of bovine liver catalase.A greenish color develops, which at T = 4°C turnsinto dark red after one minute. This is an indicationthat the tyrosyl is formed (it is not the color of thetyrosyl radical !).EPR suggests the conversion of TYR369 into theradical state with a yield of up to 80% .
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Time resolved polarised neutron scattering wasmeasured in time slots of 50 milliseconds at the instrumentD22 of the Institut Laue Langevin
The direction of proton spin polarisation was changed each5 seconds.For a fast change of the microwave frequency, twomicrowave sources tuned to slightly different frequencieswere run in parallel, and used in an alternating mode.
0 5 10 12time [ seconds]
negative DNP positive DNP
100 time slots of 50 ms 100 time slots of 50 ms storage time
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The results of time-resolved polarised neutron scattering fromdynamically polarised proton spin targets were obtained by acollaborating team consisting of
Ben van den BrandtPatrick HautleJoachim KohlbrecherTon KonterSalvatore Mango Paul-Scherrer-Institut, Villigen, Schweiz
Hans GlättliEdouard Leymarie CEA, Saclay, France
Jaques Gaillard CEA, Grenoble
Eric FanchonHélène JouveRichard Kahn Institut de Biologie Structurale Jean-Pierre
Ebel, CEA/CNRS, Grenoble, France
Heinrich Stuhrmann GKSS and IBS, Grenoble, France
Oliver Zimmer Technische Universität München, Germany
Isabelle GrilloRoland May Institut Laue-Langevin, Grenoble, France
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EPR of the tyrosyl radical
97.3 GHz(2.8 mm microwaves)
-150 MHz +150 MHz
negative nuclear spin polarisationpositive nuclear
spin polarisation
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1000
10000
100000
1000000
0 50 100 150 200 250
momentum transfer Q [1000/A]
inte
ns
ity
neutron small-angle scattering of a frozen solution of catalaseo measured--- calculated
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Remember
The polarisation is driven to more negative values during thefirst 5 seconds and then to more positive values during thefollowing 5 seconds. Repetition: many thousand times.
0 5 10 12time [ seconds]
negative DNP positive DNP
100 time slots of 50 ms 100 time slots of 50 ms storage time
EPR of the tyrosyl radical
97.3 GHz(2.8 mm microwaves)
-150 MHz +150 MHz
negative nuclear spin polarisationpositive nuclear
spin polarisation
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Internal relaxation:
space and time resolved proton spin polarisation diffusion in tyrosyl doped catalase,
negative DNP
-700
-600
-500
-400
-300
-200
-100
0
100
0 10 20 30 40 50 60 70 80 90radius [A]
dens
ity
t=0.10t=0.20t=0.30t=0.40t=0.50t=1.00t=2.00t=3.00t=4.00t=5.00
radius of tetramer catalase
space and time resolved proton spin polarisation diffusion in tyrosyl doped catalase
positive DNP
-600
-500
-400
-300
-200
-100
0
100
200
300
400
0 10 20 30 40 50 60 70 80 90radius [A]
dens
ity
t=0.05t=0.10t=0.20t=0.30t=0.40t=0.50t=1.00t=2.00t=3.00t=4.00t=4.50t=5.00
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Scattering from catalase , in vacuo
10
100
1000
10000
100000
1000000
10000000
100000000
0 50 100 150 200 250
Q [1000/A]
inte
nsity
0123456789101112all
I(Q) = Σl=0L Σm=-l
l IAlm(Q)I2
Σm=-ll IAlm(Q)I2
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Data analysis:
I(Q,t) from time resolved neutron scattering
d I(Q,t) / dt this eliminates the scattering which does not vary with time
find relaxation times τn:d I(Q,t) / dt = Σn Gn(Q) exp(−t/τn) n=1,2,3
Describe Gn(Q) by a polynomial :Gn(Q) = (an,0 + an,1Q2 + .....an,6 Q12) exp(− bQ2)
Small-angle scattering:
Monopole approximation ( neglect higher multipoles)
The time dependent amplitude then is
nF00(Q) ≡ Gn(Q) / I00(Q)(catalase)
Fourier transform to real space:
nρoo( r ) = nFoo (Q) sin(Qr)/Qr Q2 dQ
Time dependent radial density of catalase
d ρ(r,t) / dt = Σn nρ00(r) exp(−cn t)
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-6000
-4000
-2000
0
2000
4000
6000
-8000 -6000 -4000 -2000 0 2000 4000 6000 8000
subuni t_1
subuni t_2
subuni t_3
subuni t_4
tyr_369
heme
catalase: x,z plane:the tyrosyls are inside a sphere of 15 A
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The results of time-resolved polarised neutron scattering from dynamically polarisedproton spins were obtained by a collaborating team consisting of
Ben van den BrandtPatrick HautleJoachim KohlbrecherTon KonterSalvatore Mango Paul-Scherrer Institut Villigen, Schweiz
Hans GlättliEdouard Leymarie CEA, Saclay
Jaques Gaillard CEA Grenoble
Eric FanchonHélène JouveRichard Kahn Institut de Biologie Structurale Jean-Pierre Ebel,
CEA/CNRS, Grenoble, France
Heinrich Stuhrmann GKSS and IBS, Grenoble, France
Oliver Zimmer Technische Universität München, Germany
Isabelle GrilloRoland May Institut Laue Langevin
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Ways of contrast variation
1) X-ray and neutron scattering:
Solvent density variation by addition of low molecularcompoundsMethods of isomorphous replacement.
Resonant scattering(Multi-wavelength Anomalous Solvent Contrast, (MASC) ifapplied to solvent)
Neutron scattering :
Isotopic substitution , mostly deuteration- static experiments ( deuteration of solvent, specific
labelling of the macromolecule)- kinetic of isotope exchange (H/D exchange with
solvent)
Polarized neutron scattering:(absence of neutron polarisation weakens the signal)
Nuclear spin polarisation
- static experiments, often with 'pre-contrasting' bydeuteration
- dynamic experiments: creation and of selectivelypolarized proton spin domains and their internalrelaxation near paramagnetic centres.
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Contrast with macromolecules :
Radiation interacts with atoms and/or their nuclei.
For the present pourpose, the strength of intertaction isdescribed by the scattering length b.
In a volume containing a reasonably large number of atomsit is convenient to define the scattering length density (orscattering density) :
ρ = Σn bn / volume
For a macromolecule in solution:
Contrast : ρ ( r ) : = ρ ( r )MM - ρ solvent
Internal contrast:
ρ = ρ(x,y,z) = ρ (r) .
as opposed to
External contrast (or solvent dependent contrast)
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If the con tras t is m ade to va ry, then we have
Contrast variation
varia tio n of solvent density(external co ntrast varia tion,or solvent co ntrast variation )
varia tio n of the scattering density of parts of am acrom olecule(in tern al contrast v aria tion)
From real spaceto momentum space
A(Q ) = v ρ(r) exp(iQr) dv
|Q | = 4 π s in θ / λ , 2θ = scattering ang le, λ = waveleng th
A(Q ) = U(Q ) + x V(Q )
↑↑↑↑ contras t, in a w id e sense
T he expres sion for the intensity I(Q ) m ay vary. In thesim plest case it is g iven b y
I(Q) = |U(Q)|2+ x 2Re[U(Q)V*(Q)] + x2 |V(Q)|2
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For small-angle scattering from randomlyoriented particles I(Q) is the the result of anintegration over all orientations of the dissolvedparticles. The basic scattering functions areobtained by variation of x.
Contrast variation startet with X-ray diffraction fom a hemoglobincrystal ( Bragg & Perutz, 1952).
Considerable changes of the low order reflections of hemoglobinwere observed with the varaition of the electron density of thesolvent.
packing of the hemoglobin molecules in the unit cell
This method is the precursor of multiwavelength anomalous solventcontrast variation (MASC) (Fourme et al. 1995)
x = f ' + i f ''
Hence
I(Q) = |U(Q)|2+ f ' 2Re[U(Q)V*(Q)] + f '' 2Im[U(Q)V*(Q)]
+ (f '2 + f ''2 ) |V(Q)|2
Note the presence of four basic scattering functions
shape and packing of the proteins in the unit cell.
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Anomalous small-angle scattering
I(Q) = |U(Q)|2+ f ' 2Re[U(Q)V*(Q)] +(f '2 + f ''2 ) |V(Q)|2 dΩ
Example: phosphorus of rRNA of the large ribosomal subunit.Anomalous dispersion at wavelengths near the K-edge ofphosphorus ( λλλλ = 5.76 Å ) (M. Hütsch, 1995)
Variation of anomalous scattering length with λ: 16 e.u.( 1 e.u. = scattering length of one electron = 0.28E-12 cm )Local concentration of P : up to 3 M / l
in situ structure of rRNA at low resolution
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In the mid sixties, solvent contrast variation was used in small-anglescattering. The electron density was varied by addition of glycerol orsugar. Variation of the radius of gyration with contrast inmyoglobin.
With the advent of high flux neutron sources, contrast variation isalmost entirely done byexchange of the hydrogen isotope 1H by 2H (Deuterium).
- High abundance: 70 H / nm3 (110 M/l)
- Large change of scattering length: 0.69E-12 cm (corresponds to the scattering length of 2.5 electrons in X-ray scattering).
Applications of solvent contrast variation were numerous :
Ribosomes, Chromatin, RNA polymerase,Viruses,Lipoproteins
The constituents of these particles are
H / nm3 scattering density matched by
RNA/DNA 40 high 70% D2O
Proteins 60 medium 40% D2O
Lipids 70 low water low resolution architecture (quaternary structure)
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Examples of internal contrast variation:
Ribosomes:
The positions of all 21 proteins of the small ribosomal subunit were foundby triangulation between specific deuteratedribosomal proteins ( D.M. Engelman & P.B. Moore, W. Hoppe).
The method of triple isomorphous replacement uses fully andpartially deuterated proteins as labels (I. Serdyuk).
It resembles in some respects a method which uses the
change of the scattering length of hydrogen with protonspin polarisation in polarised neutron small-anglescattering.
x = P ( = proton spin polarisation)
The intensity of polarised neutron small-angle scattering is
I↑↑(Q) = |U(Q)|2 + P 2Re[U(Q)V*(Q)] + P2 |V(Q)|2 dΩ
if the direction proton spins coincides with that of the neutron spins
I↓↑ (Q) = |U(Q)|2 – P 2Re[U(Q)V*(Q)] + P2 |V(Q)|2 dΩ
if the direction proton spins is opposite to that of the neutron spins
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The method of proton spin contrast variation was used todetemine the in situ structure of the tRNAs and of themRNA, i.e. the position and orientation of thesemolecules inside the the functional ribosome.
Largest variation of the scattering length with thepolarisation of the proton spins:
(− 0.56 ± 1.456 P) 10-12 cm
corresponding to 10 electron units in X-ray scattering
Best results are obtained with particles which have been deuterated.Only the regions of interest are left protiated.For biological macromolecules a mixture of deuterated glycerol andheavy water is a convenient solvent.
The deuterons are polarised as well, although to an extent which ismuch lower than that of the protons: Their scattering length changesas well:
(0.66 ±0.27 P(D)) 10-12 cm