Quantifying a biophysical model of lipid-protein, lipid-DNA interactions in crowded molecular environments

Some estimates suggest that up to 80 per cent of the proteins in cells interact with a biological membrane in one way or another. Developing quantitative models of the interaction of phospholipid membranes with proteins and DNA (since it is well established that there are lipid-DNA interactions in the cell nucleus), is critical to understanding the biochemical roles of these proteins in healthy cells and ultimately treating unhealthy cells. Quantitative knowledge of a couple of key physical properties of phospholipids is vital to developing these biophysical models. The most vital is a lipid’s spontaneous curvature.

There are many hundreds of different lipids in cells and comparatively few values of the spontaneous curvature of these lipids in the scientific literature. This is because, traditionally, determining lipid spontaneous curvatures is a very slow process requiring small angle x-ray analysis studies on a large number of expensive lipid mixtures. In this project we are using small angle x-ray diffraction to develop new methodology to rapidly and cheaply determine the spontaneous curvature of lipids.

Small-angle-x-ray-diffractogram-final

Small angle x-ray diffractogram of the phospholipid dioleoylphosphatidylcholine (DOPE).

Using these spontaneous curvature values we develop fundamental quantitative models of the interaction of proteins with lipid membranes focusing in particular on the biochemical pathways through which lipids are synthesised in cells. In the later stages of the project we will look at how crowded molecular environments with large numbers of biomolecules influence these lipid spontaneous curvatures and the activity of membrane proteins.

Project timeframe

The project began in 2010 and is supported by Max Lab IV under beamtime proposals 20120231 and 2012033.

Project aims

The project aims to:

  • develop new experimental techniques that enable lipid spontaneous curvatures to be obtained rapidly.
  • determine the spontaneous curvatures of common phospholipids and mixtures of these phospholipids with biological molecules like cholesterol that mimic real biological membranes.
  • quantify the role of lipid spontaneous curvature in activating membrane interacting proteins.
  • quantify the influence of crowded molecular environments on lipid spontaneous curvatures and membrane interacting proteins

Project findings and impact

To date we have:

  • identified a rapid method to obtain lipid spontaneous curvatures by small angle x-ray diffraction.
  • determined the spontaneous curvature of a large number of phospholipids using our new method.
  • quantified the activity of key proteins involved in lipid biosynthesis relating activity to the spontaneous curvatures of lipids.

Impact

The techniques and data we have produced, and are now in the process of publishing, enable lipid spontaneous curvatures to be rapidly determined and lay the foundation for future projects and for other researchers to build computational models of the cellular membrane that accurately capture the biophysical relationships between lipids and proteins.

Research team

Dr Marcus Dymond

Yuzhang Wei (MSc Student 2016)

Isabel Mayoral Delgado (MSc Student 2015)

 

Output

Dymond, M. K., Gillams, R. J., Parker, D. J., Burrell, J., Labrador, A., Nylander, T., & Attard, G. S. (2016). Lipid Spontaneous Curvatures Estimated from Temperature-Dependent Changes in Inverse Hexagonal Phase Lattice Parameters: Effects of Metal Cations. Langmuir, 32(39), 10083-10092.

Gillams, R. J., Nylander, T., Plivelic, T. S., Dymond, M. K., & Attard, G. S. (2014). Formation of inverse topology lyotropic phases in dioleoylphosphatidylcholine/oleic acid and dioleoylphosphatidylethanolamine/oleic acid binary mixtures. Langmuir, 30(12), 3337-3344.

Tsaloglou, M. N., Attard, G. S., & Dymond, M. K. (2011). The effect of lipids on the enzymatic activity of 6-phosphofructo-1-kinase from B. stearothermophilus. Chemistry and physics of lipids, 164(8), 713-721.

Wilson, R. J., Tyas, S. R., Black, C. F., Dymond, M. K., & Attard, G. S. (2010). Partitioning of ss RNA Molecules between Preformed Monolithic HII Liquid Crystalline Phases of Lipids and Supernatant Isotropic Phases. Biomacromolecules, 11(11), 3022-3027.

Black, C. F., Wilson, R. J., Nylander, T., Dymond, M. K., & Attard, G. S. (2010). Linear ds DNA Partitions Spontaneously into the Inverse Hexagonal Lyotropic Liquid Crystalline Phases of Phospholipids. Journal of the American Chemical Society, 132(28), 9728-9732.

Partners

George Attard (University of Southampton).

Tommy Nylander (University of Lund)

Richard Gillams (University of Oxford)