Download Investigating the organization, assembly and physical properties of

Investigating the organization, assembly and physical properties of the unique lipids
of thylakoid membranes
Dr. Peter Adams, Dr. Simon Connell, Prof. Stephen Evans
School of Physics & Astronomy, University of Leeds
Astbury Centre for Structural Molecular Biology, University of Leeds
Biological cells and some internal structures are surrounded by membranes comprised of
lipid bilayers and membrane proteins. Certain specialized biomembranes are stacked into
multi-layers, allowing a high content of protein-lipid bilayers in a small volume. Chloroplasts
(the photosynthetic organelle found within plant cells) contain a network of stacked
membranes, termed “thylakoids”, specialized for photosynthesis (1). The increased surface
area allowed by this membrane organization is important for enhancing the chloroplast’s
capacity for energy trapping. The unusual lipids found within thylakoid membranes appear to
play an essential structural role in maintaining this organization, however, they are relatively
unstudied (2). This PhD project would characterize the physical properties, dynamic
organization and assembly of stacked architectures of thylakoid lipids, in order to better
understand the biophysical basis of the natural membrane system (experimental/
biophysics).
The thylakoid lipid MGDG (monogalactosyl diglyceride) has a high degree of negative
curvature, whereas DGDG (digalactosyl diglyceride) is relatively planar; other thylakoid lipids
(SQDG and PG) provide charged groups. We will systematically vary the relative ratios of
each lipid and characterize how this affects the system, as follows. The lipid bilayer surface
structure will be visualized with atomic force microscopy at high spatial resolution (subnanometer), revealing phase segregation in single layers and the height of stacked
membrane layers. Neutron reflectivity will be used to characterize bilayer thickness and
number of multilayers. Differential scanning calorimetry and Langmuir trough measurements
will reveal how melting transition temperature and lipid density varies. Fluorescence
microscopy will allow observation of mobile lipid multilayer membranes and tracking of
membrane fluidity. Finally, experiments incorporating photosynthetic proteins at increasing
concentrations into our test membranes will reveal their effect on membrane assembly.
Analysis of these experiments is expected to reveal the mechanisms driving the
fundamentally-important curvature and multilayer stacking of these photosynthetic
membranes.
Thylakoid membrane organisation from ref (1)
University of Leeds, UK
Lipid shapes and phase behaviour from ref (2)
PhD project: 2017 entry
References/ further reading
1.
2.
Johnson, M. P., C. Vasilev, J. D. Olsen, and C. N. Hunter. 2014. Nanodomains of Cytochrome
b6f and Photosystem II Complexes in Spinach Grana Thylakoid Membranes. The Plant Cell
Online 26: 3051-3061.
Jouhet, J. 2013. Importance of the hexagonal lipid phase in biological membrane
organisation. Frontiers in Plant Science 4: 494.
University of Leeds, UK
PhD project: 2017 entry