Research 16: R Millane

1. DIFFRACTION IMAGING OF THE MYOSIN
SUPERLATTICE OF VERTEBRATE MUSCLE
Rick Millane, David Wojtas, Chunhong Yoon* and John Squire+
Department of Electrical and Computer Engineering
University of Canterbury
*Department of Physics, University of Wisconsin - Milwaukee, USA
+Department of Physiology and Pharmacology
University of Bristol, Bristol, UK
New Zealand Institute of Physics Conference
Wellington, 17-19 October 2011
Supported in part by the Marsden Fund
1

2. Outline
• Myosin lattice of vertebrate muscle
• Electron microscopy and x-ray fibre diffraction
• Image analysis
• Disordered systems – frustration – statistical physics
• X-ray diffraction
• Conclusions
2

3. Imaging and diffraction imaging
Microscopy
light
electrons
specimen FT lens image
Diffraction Imaging
x-rays
computer
electrons
image
specimen diffraction
pattern
3

4. Myosin lattice
Muscle fibre
myofibril
sarcomere
4

5. Myosin lattice
Simple lattice Superlattice
Rotational disorder
5

6. Electron microscopy and image analysis
Close up
Cross-section of sarcomere
Template
Template for
for rotations
locations
6

7. Classification of orientations
7

8. Distribution of orientations
8

9. Geometrically frustrated systems
A spin system, for example, for which as, a result of lattice topology,
the energy of each spin pair cannot be simultaneously minimised.
A very simple classical example is a triangular lattice with
antiferromagnetic interactions.
I.e. “unlike’ spins, or states, are energetically preferred.
It is not possible to satisfy the constraints on each elementary
plaquette of the lattice.
Leads to a large number of ground states.
?
This is the triangular Ising antiferromagnet – TIA.
Characterised using spin-pair correlations.
9

10. TIA correlations
Different
temperatures
Partitioned into
two sublattices
10

11. Spatial correlations – myosin lattice and TIA
Observed – myosin lattice
TIA by Monte Carlo simulation
11

12. Myosin lattice disorder – measured and simulated
Myosin lattice TIA
12

13. X-ray fibre diffraction patterns from muscle
13

14. Fibre diffraction pattern from relaxed frog muscle
Iwamoto et al., Biophys. J., 85, 2492-2506 (2003).
14

15. Measured diffraction data – layer line amplitudes
15

16. Simulation of x-ray diffraction from the myosin array
Develop methods to simulate x-ray
diffraction from models of the
myosin filament.
Need to incorporate:
The molecular structure and helical
symmetry.
The TIA disorder.
Cylindrical averaging.
16

17. Calculated diffraction – ordered crystalline specimen
17

18. Calculated diffraction – completely disordered
18

19. Calculated diffraction – TIA disorder
19

20. Summary
• The superlattice disorder observed in the myosin
lattice of higher verebrate muscle is a manifestation of
a frustrated system.
• The frustration is due to incompatible preferred
interactions between the myosin filaments.
• This may have evolutionary significance for muscle
function.
• Direct (electron microscopy) and diffraction (x-ray
diffraction) imaging complement each other.
• Effects of disorder can be incorporated into diffraction
calculations to allow rigorous analysis of diffraction
data.
• Engineers and biophysicists can work productively
together and have lots of fun!
20