14.04 o14 r millane
-
Upload
nzip -
Category
Technology
-
view
255 -
download
0
description
Transcript of 14.04 o14 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 EngineeringUniversity of Canterbury
*Department of Physics, University of Wisconsin - Milwaukee, USA
+Department of Physiology and PharmacologyUniversity of Bristol, Bristol, UK
New Zealand Institute of Physics ConferenceWellington, 17-19 October 2011
Supported in part by the Marsden Fund
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
3
Imaging and diffraction imaging
light
electrons
specimen FT lens image
Microscopy
x-rays
electrons
specimen diffraction pattern
image
Diffraction Imaging
computer
4
Myosin lattice
myofibril
sarcomere
Muscle fibre
5
Myosin lattice
Simple lattice SuperlatticeRotational disorder
6
Electron microscopy and image analysis
Close up
Cross-section of sarcomere
Templateforrotations
Templateforlocations
7
Classification of orientations
8
Distribution of orientations
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.
10
TIA correlations
Differenttemperatures
Partitioned intotwo sublattices
11
Spatial correlations – myosin lattice and TIA
Observed – myosin latticeTIA by Monte Carlo simulation
12
Myosin lattice disorder – measured and simulated
Myosin lattice TIA
13
X-ray fibre diffraction patterns from muscle
14
Fibre diffraction pattern from relaxed frog muscle
Iwamoto et al., Biophys. J., 85, 2492-2506 (2003).
15
Measured diffraction data – layer line amplitudes
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.
17
Calculated diffraction – ordered crystalline specimen
18
Calculated diffraction – completely disordered
19
Calculated diffraction – TIA disorder
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!